Cannabis Maturation and Harvesting

by Robert Connell Clarke


The maturation of Cannabis is normally annual and its timing is influenced by the age of the plant, changes in photoperiod, and other environmental conditions. When a plant reaches an adequate age for flowering (about two months) and the nights lengthen following the summer solstice (June 21-22), flowering begins. This is the triggering of the reproductive phase of the life cycle which is followed by senescence and eventual death. The leaves of Cannabis plants form fewer leaflets during flowering until the floral clusters are formed of tri-leaflet and mono-leaflet leaves. This is a reversal of the heteroblastic (variously shaped) trend of increased leaflet number through the prefloral stage.

The staminate and pistillate sexes of the same strain mature at different rates. Staminate plants are usually the first to begin flowering and releasing pollen. In fact, much pollen is released when the pistillate plants show only a few pairs of primordial flowers. It would seem more effective for the staminate plant to release pollen when the pistillate plants are in heavy flower to ensure good seed production. Upon deeper investigation, however, it becomes obvious that early pollination is advantageous to survival. Pollinations that take place early form seeds that ripen in the warm days of summer when the pistillate plant is healthy and there is less chance of frost damage or predation by herbivores. If conditions are favorable, the staminate plant will continue to produce pollen for some time and will also fertilize many new pistillate flowers as they appear. After a month or more of shedding pollen the staminate plants enter senescence. This period is marked by the yellowing and dropping of the foliage leaves, followed by diminished flower and pollen production. Eventually, all the leaves drop, and the spent, lifeless stamens hang in the breeze until fungi and bacteria return them to the soil.

Pistillate plants continue to develop up to three months longer as they mature seeds. As the calyxes of the first flowers to be pollinated dry out, each releases a single seed which falls to the ground. Since new pistillate flowers are continually produced and fertilized, there are nearly always seeds ranging in maturity from freshly fertilized ovules to large, dark, mature seeds. In this way the plant is able to take advantage of favorable conditions throughout several months. The effectiveness of this type of reproduction is demonstrated by the spread of escaped Cannabis strains in the midwestern United States. In these areas Cannabis abounds and multiplies each year, through the timely dehiscence of millions of pollen grains and the fertilization of thousands of pistillate flowers, resulting in thousands of viable seeds from each pistillate plant. As the pistillate plant senesces, the leaves turn yellow and drop, along with the remaining mature seeds. The rest of the plant eventually dies and decomposes.

Although the staminate plants begin to release pollen before the pistillate plant has begun to form floral clusters, pistillate plants actually differentiate sexually and form a few viable flowers long before most of the staminate plants begin to release pollen. This ensures that the first pollen released has a chance to fertilize at least a few flowers and produce seeds. The production of prominent pistils makes pistillate plants the first to be recognizable in a crop, so early selection of seed-parents is quite easy. Often the primordia of staminate plants first appear as vegetative growth at the nodes along the main stalk and do not differentiate flowers for several weeks. Pistillate plants also may develop vegetative growth in place of the usual primordial calyxes and this growth makes staminate plants indistinguishable from pistillate plants for some time. This is often frustrating to sinsemilla Cannabis cultivators, since the staminate plants that are hesitant to differentiate sex take up valuable space that could be utilized by pistillate plants. Also, juvenile pistillate plants are occasionally mistaken for staminate plants if they are slow to form calyxes, since vegetative growth at the nodes could appear to be staminate primordia.

Latitude and Photoperiod

Change in photoperiod is the factor that usually triggers the developmental stages of Cannabis. Photoperiod and seasonal cycles are determined by latitude. The most even photoperiods and mildest seasonal variations are found near the equator, and the most widely fluctuating photoperiods and most radical seasonal variations are found in polar and high altitude locations. Areas in intermediate latitudes show more pronounced seasonal variation depending on their distance from the equator or height in altitude. A graph of light cycles based on latitude is helpful in exploring the maturation and cycles of Cannabis from various latitudes and the genetic adaptations of strains to their native environments.

The wavy lines follow the changes in photoperiod (daylength) for two years at various latitudes. Follow, for example, the photoperiod for 400 north latitude (Northern California) which begins along the left-hand margin with a 15-hour photoperiod on June 21 (summer solstice). As the months progress to the right, the days get shorter and the line representing photoperiod slopes downward. During July the daylength decreases to 14 hours and Cannabis plants begin to flower and produce THC. (Increased THC production is represented by an increase in the size of the dots along the line of photoperiod.) As the days get shorter the plants flower more profusely and produce more THC until a peak period is reached during October and November. After this time the photoperiod drops below 10 hours and THC production slows. High-THC plants may continue to develop until the winter solstice (shortest day of the year, around December 21) if they are protected from frost. At this point a new vegetative light cycle starts and THC production ceases. New seedlings are planted when the days begin to get long (12-14 hours) and warm from March to May. Farther north at 600 latitude the day length changes more radically and the growing season is shorter. These conditions do not favor THC production.

Light cycles and seasons vary as one approaches the equator. Near 200 north latitude (Hawaii, India, and Thailand where most of the finest Cannabis originates), the photoperiod never varies out of the range critical for THC production, between 10 and 14 hours. The light cycle at 200 north latitude starts at the summer solstice when the photoperiod is just a little over 13 hours. This means that a long season exists that starts earlier and finishes later than at higher latitudes. However, because the photoperiod is never too long to induce flowering, Cannabis may also be grown in a short season from December through March or April (90 to 120 days). Strains from these latitudes are often not as responsive to photoperiod change, and flowering seems strongly age-determined as well as light determined. Most strains of Cannabis will begin to flower when they are 60 days old if photoperiod does not exceed 13 hours. At 200 latitude, the photoperiod never exceeds 14 hours, and easily induced strains may begin flowering at nearly any time during the year.

Equatorial areas gain and lose daylength twice duringthe year as the sun passes north and south of the equator, resulting in two identical photoperiodic seasons. Rainfall snd altitude determine the growing season of each area, but at some locations along the equator it is possible to grow two crops of fully mature Cannabis in one year. By locating a particular latitude on the chart, and noting local dates for the last and first frosts and wet and dry seasons, the effective growing season may be determined. If an area has too short an effective growing season for Cannabis, a greenhouse or other shelter from cold, rainy conditions is used. The timing of planting and length of the growing season in these marginal conditions can also be determined from this chart.

For instance, assume a researcher wishes to grow a crop of Cannabis near Durban, South Africa, at 300 south latitude. Consulting the graph of maturation cycles will reveal that a long-photoperiod season, adequate for the maturation of Cannabis, exists from October through June. Local weather conditions indicate that average temperature ranges from 60~ to 80~ F. and annual precipitation from 30 to 50 inches. Early storms from the east in June could damage plants and some sort of storm protection might be necessary. Any estimates made from this chart sre generally accurate for photoperiod; however, local weather conditions are always taken into account. Combination and simplification of the earth’s climatic bands where Cannabis is grown yields an equatorial zone, north and south subtropical zones, north and south temperate zones, arctic and antarctic zones. A discussion of the maturation cycle for Cannabis in each zone follows.

Equatorial Zone – (15 south latitude to 15 north latitude)

At the equator the sun is high in the sky all year long. The sun is directly overhead twice a year at the equinoxes, March 22 and September 22, as it passes to the north and then the south. The days get shortest twice a year on each equinox. As a result, the equatorial zone has two times during the year when floral induction can take place and two distinct seasons, These seasons may overlap but they are usually five to six months long and unless the weather forbids, the fields may be used twice a year. Colombia, southern India, Thailand, and Malawi all lie on the fringes of the equatorial zone between 10 and 15 latitude. It is interesting to note that few if any areas of commercial Cannabis cultivation, other than Colombia, lie within the heart of the equatorial zone. This could be because most areas along the equator or very near to it are extremely humid at lower altitudes, so it may be impossible to find a dry enough place to grow one crop of Cannabis, much less two. Wild Cannabis occurs in many equatorial areas but it is of relatively low quality for fiber or bud production. Under cultivation, however, equatorial Cannabis has great potential for bud production.

Northern and Southern Subtropical Zones – (15 to 30 north and south latitudes)

The northern subtropical zone is one of the largest Cannabis producing areas in the world, while the southern subtropical zone has little Cannabis. These areas usually have a long season from February-March through October-December in the northern hemisphere and from September-October through March-June in the southern hemisphere. A short season may also exist from December or January through March or April in the northern hemisphere, spanning from 90 to 120 days. In Hawaii, Cannabis cultivators sometimes make use of a third short season from June through September or September through December, but these short seasons actually break up the long subtropical season during which some of the world’s most potent Cannabis is grown. Southeast Asia, Hawaii, Mexico, Jamaica, Pakistan, Nepal, and India are all major Cannabis producing areas located in the northern subtropical zone.

North and South Temperate Zones – (30 to 60 north and south latitudes)

The temperate zones have one medium to long season stretching from March-May through September-December in the northern hemisphere and from September-November through March-June in the southern hemisphere. Central China, Korea, Japan, United States, southern Europe, Morocco, Turkey, Lebanon, Iran, Afghanistan, Pakistan, India, and Kashmir are all in the north temperate zone. Many of these nations are producers of large amounts of fiber as well as Cannabis. The south temperate zone includes only the southern portions of Australia, South America, and Africa. Some Cannabis grows in all three of these areas, but none of them are well known for the cultivation of Cannabis.

Arctic and Antarctic Zones – (60 to 70 north and south latitudes)

The arctic and antarctic zones are characterized by a short, harsh growing season that is not favorable for the growth of Cannabis, The arctic season begins during the very long days of June or July, as soon as the ground thaws, and continues until the first freezes of September or October. The photoperiod is very long when the seedlings appear, but the days rapidly get shorter and by September the plants begin to flower. Plants often get quite large in these areas, but they do not get a long enough season to mature completely and the cultivation of Cannabis is not practical without a greenhouse. Parts of Russia, Alaska, Canada, and northern Europe are within the arctic zone and only small stands of escaped fiber and Cannabis grow naturally. Cultivated bud strains are grown in Alaska, Canada, and northern Europe in limited quantities but little is grown on a commercial scale. Rapidly maturing, acclimatized hybrid strains from temperate North America are probably the best suited for growth in this area. Fiber strains also grow well in some arctic areas. Breeding programs with Russian Cannabis ruderalis could yield very short season bud strains.

It becomes readily apparent that most of the Cannabis occurs in the northern subtropical and northern temperate zones of the world. It is striking that there are many unutilized areas suitable for the cultivation of Cannabis the world over. It is also readily apparent that the equatorial zone and subtropical zones have the advantage of an extra full or partial season for the cultivation of Cannabis.

Strains that have become adapted to their native latitude will tend to flower and mature under domestic cultivation in much the same pattern as they would in their native conditions. For example, in northern temperate areas, strains from Mexico (subtropical zone) will usually completely mature by the end of October while strains from Colombia (equatorial zone) will usually not mature until December. By understanding this, strains may be selected from latitudes similar to the area to be cultivated so that the chances of growing Cannabis to maturity are maximized. The short season of Hawaii, Mexico, and other subtropical areas constitutes a separate set of environmental factors (distinct from the long season) that influence genotype and favor selection of a separate short season strain. The maturation characteristics can vary greatly between these two strains because of the length of the season and differences in response to photoperiod. For that reason, it is usually necessary to determine if Hawaii and California strains have been bred specifically for either the short or long season, or if they are used indiscriminately for both seasons. Sometimes the only information available is what season the ~1 seed plant was grown. It may not be practical to grow a long-season strain from Hawaii in a temperate growing area, but a short season strain might do very well.

Moon Cycles

Since ancient times man has observed the effect of the moon on living organisms, especially his crops. Planting and harvest dates based on moon cycles are still found in the Old Farmer’s Almanac. The moon takes 28 to 29 days to completely orbit the earth. This cycle is divided into four one-week phases. It starts as the new moon waxes (begins to enlarge) for a week until the quarter moon and another week until the moon is full. Then the waning (shrinking) cycle begins and the moon passes back for two weeks through another quarter to reach the beginning of the cycle with a new moon. Most cultivators agree that the best time for planting is on the waxing moon, and the best time to harvest is on the waning moon. Exact new moons, full moons, and quarter moons are avoided as these are times of interplanetary stress. Planting, germinating, grafting, and layering are most favored during phases 1 and 2. The best time is a few days before the full moon. Phases 3 and 4 are most beneficial for harvesting and pruning.

Root growth seems accelerated at the time of the new moon, possibly as a response to increased gravitational pull from the alignment of sun and moon. It also seems that floral cluster formation is slowed by the full moon. Strong, full moonlight is on the borderline of being enough light to cease floral induction entirely. Although this never happens, if a plant is just about to begin floral growth, it may be delayed a week by a few nights of bright moonlight. Conversely, plants begin floral growth during the dark nights of the new moon. More research is needed to explain the mysterious effects of moon cycles on Cannabis.

Floral Maturation

The individual pistillate calyxes and the composite floral clusters change as they mature. External changes indicate that internal biochemical metabolic changes are also occurring. When the external changes can be connected with the invisible internal metabolic changes, then the cultivator is in a better position to decide when to harvest floral clusters. With years of experience this becomes intuition, but there are general correlations which can put the process in more objective terms.

The calyxes first appear as single, thin, tubular, green sheaths surrounding an ovule at the basal attached end with a pair of thin white, yellowish green, or purple pistils attached to the ovule and protruding from the tip fold of the calyx. As the flower begins to age and mature, the pistils grow longer and the calyx enlarges slightly to its full length. Next, the calyx begins to swell as resin secretion increases, and the pistils reach their peak of reproductive ripeness. From this point on, the pistils begin to swell and darken slightly, and the tips may begin to curl and turn reddish brown. At this stage the pistillate flower is past its reproductive peak, and it is not likely that it will produce a viable seed if pollinated. Without pollination the calyx begins to swell almost as if it had been fertilized and resin secretion reaches a peak. The pistils eventually wither and turn a reddish or orange brown. By this time, the swollen calyx has accumulated an incredible layer of resin, but secretion has slowed and few fresh terpenes and cannabinoids are being produced. Falling pistils mark the end of the developmental cycle of the individual pistillate calyx. The resins turn opaque and the calyx begins to die. The biosynthesis of cannabinoids and terpenes parallels the developmental stages of the calyx and associated resin-producing glandular trichomes. Also, the average developmental stage of the accumulated individual calyxes determines the maturational state of the entire floral cluster. Thus, determination of maturational stage and timing of the harvest is based on the average calyx and resin condition, along with general trends in morphology and development of the plant as a whole.

The basic morphological characteristics of floral maturation are measured by calyx-to-leaf ratio and internode length within floral clusters. Calyx-to-leaf ratios are highest during the peak floral stage. Later stages are usually characterized by decreased calyx growth and increased leaf growth. Internode length is usually very short between pairs of calyxes in tight dense clusters. At the end of the maturation cycle, if there is still growth, the internode length may increase in response to increased humidity and lowered light conditions. This is most often a sign that the floral clusters are past their reproductive peak; if so, they are preparing for rejuvenation and the possibility of regrowth the following season. At this time nearly all resin secretion has ceased at temperate latitudes (due to low temperatures), but may still continue in equatorial and subtropical areas that have a longer and warmer growing season. Greenhouses have been used in temperate latitudes to simulate tropical environments and extend the period of resin production. It should be remembered that greenhouses also tend to cause a stretched condition in the floral clusters in response to high humidity, high temperatures, lowered light intensity, and restricted air circulation. Simulation of the native photoperiod of a certain strain is achieved through the use of blackout curtains and supplemental lighting in a greenhouse or indoor environment. The localized light cycle particular to a strain may be estimated from the graph of maturation patterns at various latitudes. In this way it is possible to reproduce exotic foreign environments to more accurately study Cannabis. Tight clusters of calyxes and leaves are characteristic of ripe outdoor Cannabis. Some strains, however, such as those from Thailand, tend to have longer internodes and appear airy and stretched. This seems to be a genetically controlled adaptation to their native environment. Imported ~1 examples from Thailand also have long internodes in the pistillate floral clusters. Thai strains may not develop tight floral clusters even in the most arid and exposed conditions; however, this condition is furthered as rejuvenation begins during autumn days of decreasing photoperiod.

Cannabinoid Biosynthesis

Since resin secretion and associated terpenoid and cannabinoid biosynthesis are at their peak just after the pistils have begun to turn brown but before the calyx stops growing, it seems obvious that floral clusters should be harvested during this time. More subtle variations in terpenoid and cannabinoid levels also take place within this period of maximum resin secretion, and these variations influence the nature of the resin’s psychoactive effect.

The cannabinoid ratios characteristic of a strain are primarily determined by genes, but it must be remembered that many environmental factors, such as light, temperature, and humidity, influence the path of a molecule along the cannabinoid biosynthetic pathway. These environmental factors can cause an atypical final cannabinoid profile (cannabinoid levels and ratios). Not all cannabinoid molecules begin their journey through the pathway at the same time, nor do all of them complete the cycle and turn into THC molecules simultaneously. There is no magical way to influence the cannabinoid biosynthesis to favor THC production, but certain factors involved in the growth and maturation of Cannabis do affect final cannabinoid levels, These factors may be controlled to some extent by proper selection of mature floral clusters for harvesting, agricultural technique, and local environment. In addition to genetic and seasonal influences, the picture is further modified by the fact that each individual calyx goes through the cannabinoid cycle fairly independently and that during peak periods of resin secretion new flowers are produced every day and begin their own cycle. This means that at any given time the ratio of calyx-to-leaf, the average calyx condition, the condition of the resins, and resultant cannabinoid ratios indicate which stage the floral cluster has reached. Since it is difficult for the amateur cultivator to determine the cannabinoid profile of a floral cluster without chromatographic analysis, this discussion will center on the known and theoretical correlations between the external characteristics of calyx and resin and internal cannabinoid profile. A better understanding of these subtle changes in cannabinoid ratios may be gleaned by observing the cannabinoid biosynthesis. Focus on the lower left-hand corner of the chart. Next, follow the chain of reactions until you find the four isomers of THC acid (tetrahydrocannabinolic acid), toward the right side of the page at the crest of the reaction sequence, and realize that there are several steps in a long series of reactions that precede and follow the formation of THC acids, the major psychoactive cannabinoids. Actually, THC acid and the other necessary cannabinoid acids are not psychoactive until they decarboxylate (lose an acidic carboxyl group [COOHI). It is the cannabinoid acids which move along the biosynthetic pathway, and these acids undergo the strategic reactions that determine the position of any particular cannabinoid molecule along the pathway. After the resins are secreted by the glandular trichome they begin to harden and the cannabinoid acids begin to decarboxylate. Any remaining cannabinoid acids are decarboxylated by heat within a few days after harvesting. Other THC acids with shorter side-chains also occur in certain strains of Cannabis. Several are known to be psychoactive and many more are suspected of psychoactivity. The shorter propyl (three carb on) and methyl (one-carbon) side-chain homologs (similarly shaped molecules) are shorter acting than pen tyl (five-carbon) THCs and may account for some of the quick, flashy effects noted by some marijuana users. We will focus on the pentyl pathway but it should be noted that the propyl and methyl pathways have homologs at nearly every step along the pentyl pathway and their synthesis is basically identical.

The first step in the pentyl cannabinoid biosynthetic pathway is the combination of olivetolic acid with geranyl pyrophosphate. Both of these molecules are derived from terpenes, and it is readily apparent that the biosynthetic route of the aromatic terpenoids may be a clue to formation of the cannabinoids. The union of these two molecules forms CBG acid (cannabigerolic acid) which is the basic cannabinoid precursor molecule. CBG acid may be converted to CBGM (CBG acid monomethyl ether), or a hydroxyl group (OH) attaches to the geraniol portion of the molecule forming hydroxy-CBG acid. Through the formation of a transition-state molecule, either CBC acid (cannabichromenic acid) or CBD acid (cannabidiolic acid) is formed. CBD acid is the precursor to the THC acids, and, although CBD is only mildly psychoactive by itself, it may act with THC to modify the psychoactive effect of the THC in a sedative way. CBC is also mildly psychoactive and may interact synergistically with THC to alter the psychoactive effect (Turner et al. 1975). Indeed, CBD may suppress the effect of THC and CBC may potentiate the effect of THC, although this has not yet been proven. All of the reactions along the cannabinoid biosynthetic pathway are enzyme-controlled but are affected by environmental conditions.

Conversion of CBD acid to THC acid is the single most important reaction with respect to psychoactivity in the entire pathway and the one about which we know the most. Personal communication with Raphael Mechoulam has centered around the role of ultraviolet light in the biosynthesis of THC acids and minor cannabinoids. In the laboratory, Mechoulam has converted CBD acid to THC acids by exposing a solution of CBD acid in n-hexane to ultraviolet light of 235-285 nm. for up to 48 hours. This reaction uses atmospheric oxygen molecules (02) and is irreversible; however, the yield of the conversion is only about 15% THC acid, and some of the products formed in the laboratory experiment do not occur in living specimens. Four types of isomers or slight variations of THC acids (THCA) exist. Both Delta1-THCA and Delta6-THCA are naturally occurring isomers of THCA resulting from the positions of the double bond on carbon 1 or carbon 6 of the geraniol portion of the molecule They have approximately the same psychoactive effect; however, Delta1-THC acid is about four times more prevalent than Delta6-THC acid in most strains. Also Alpha and Beta forms of Delta1-THC acid and Delta6-THC acid exist as a result of the juxtaposition of the hydrogen (H) and the carboxyl (COOH) groups on the olivetolic acid portion of the molecule It is suspected that the psychoactivity of the a and ~ forms of the THC acid molecules probably does not vary, but this has not been proven. Subtle differences in psychoactivity not detected in animals by laboratory instruments, but often discussed by marijuana aficionados, could be attributed to additional synergistic effects of the four isomers of THC acid. Total psychoactivity is attributed to the ratios of the primary cannabinoids of CBC, CBD, THC and CBN; the ratios of methyl, propyl, and pentyl homologs of these cannabinoids; and the isomeric variations of each of these cannabinoids. Myriad subtle combinations are sure to exist. Also, terpenoid and other aromatic compounds might suppress or potentiate the effects of THC.

Environmental conditions influence cannabinoid biosynthesis by modifying enzymatic systems and the resultant potency of Cannabis. High altitude environments are often more arid and exposed to more intense sunlight than lower environments. Recent studies by Mobarak et al. (1978) of Cannabis grown in Afghanistan at 1,300 meters (4,350 feet) elevation show that significantly more propyl cannabinoids are formed than the respective pentyl homologs. Other strains from this area of Asia have also exhibited the presence of propyl cannabinoids, but it cannot be discounted that altitude might influence which path of cannabinoid biosynthesis is favored. Aridity favors resin production and total cannabinoid production; however, it is unknown whether arid conditions promote THC production specifically. It is suspected that increased ultraviolet radiation might affect cannabinoid production directly. Ultraviolet light participates in the biosynthesis of THC acids from CBD acids, the conversion of CBC acids to CCY acids, and the conversion of CBD acids to CBS acids. However, it is unknown whether increased ultraviolet light might shift cannabinoid synthesis from pentyl to propyl pathways or influence the production of THC acid or CBC acid instead of CBD acid.

The ratio of THC to CBD has been used in chemotype determination by Small and others. The genetically determined inability of certain strains to convert CBD acid to THC acid makes them a member of a fiber chemotype, but if a strain has the genetically determined ability to convert CBD acid to THC acid then it is considered a bud strain. It is also interesting to note that Turner and Hadley (1973) discovered an African strain with a very high THC level and no CBD although there are fair amounts of CBC acid present in the strain. Turner* states that he has seen several strains totally devoid of CBD, but he has never seen a strain totally devoid of THC. Also, many early authors confused CBC with CBD in analyzed samples because of the proximity of their peaks on gas liquid chromatograph (GLC) results. If the biosynthetic pathway needs alteration to include an enzymatically controlled system involving the direct conversion of hydroxy-CBG acid to THC acid through allylic rearrangement of hydroxy-CBG acid and cyclization of the rearranged intermediate to THC acid, as Turner and Hadley (1973) suggest, then CBD acid would be bypassed in the cycle and its absence explained. Another possibility is that, since CBC acid is formed from the same symmetric intermediate that is allylically rearranged before forming CBD acid, CBC acid may be the accumulated intermediate, the reaction may be reversed, and through the symmetric intermediate and the usual allylic rearrangement CBD acid would be formed but directly converted to THC acid by a similar enzyme system to that which reversed the formation of CBC acid. If this happened fast enough no CBD acid would be detected. It is more likely, however, that CBDA in bud strains is converted directly to THCA as soon as it is formed and no CBD builds up. Also Turner, Hemphill, and Mahlberg (1978) found that CBC acid was contained in the tissues of Cannabis but not in the resin secreted by the glandular trichomes. In any event, these possible deviations from the accepted biosynthetic pathway provide food for thought when trying to decipher the mysteries of Cannabis strains and varieties of psychoactive effect.

Returning to the more orthodox version of the cannabinoid biosynthesis, the role of ultraviolet light should be reemphasized. It seems apparent that ultraviolet light, normally supplied in abundance by sunlight, takes part in the conversion of CBD acid to THC acids. Therefore, the lack of ultraviolet light in indoor growing situations could account for the limited psychoactivity of Cannabis grown under artificial lights. Light energy has been collected and utilized by the plant in a long series of reactions resulting in the formation of THC acids. Farther along the pathway begins the formation of degradation products not metabolically produced by the living plant. These cannabinoid acids are formed through the progressive degradation of THC acids to CBN acid (cannabinolic acid) and other cannabinoid acids. The degradation is accomplished primarily by heat and light and is not enzymatically controlled by the plant. CBN is also suspected of synergistic modification of the psychoactivity of the primary cannabinoids, THCs. The cannabinoid balance between CBC, CBD, THC, and CBN is determined by genetics and maturation. THC production is an ongoing process as long as the glandular trichome remains active. Variations in the level of THC in the same trichome as it matures are the result of THC acid being broken down to CBN acid while CBD acid is being converted to THC acid. If the rate of THC biosynthesis exceeds the rate of THC breakdown, the THC level in the trichome rises; if the breakdown rate is faster than the rate of biosynthesis, the THC level drops. Clear or slightly amber transparent resin is a sign that the glandular trichome is still active. As soon as resin secretion begins to slow, the resins will usually polymerize and harden. During the late floral stages the resin tends to darken to a transparent amber color. If it begins to deteriorate, it first turns translucent and then opaque brown or white. Near-freezing temperatures during maturation will often result in opaque white resins. During active secretion, THC acids are constantly being formed from CBD acid and breaking down into CBN acid.

Harvest Timing

With this dynamic picture of the biosynthesis and degradation of THC acids as a frame of reference, the logic behind harvesting at a specific time is easier to understand. The usual aim of timing the moment of harvest is to ensure high THC levels modified by just the proper amounts of CBC, CBD and CBN, along with their propyl homologs, to approximate the desired psychoactive effect. Since THC acids are being broken down into CBN acid at the same time they are being made from CBD acid, it is important to harvest at a time when the production of THC acids is higher than the degradation of THC acids. Every experienced cultivator inspects a number of indicating factors and knows when to harvest the desired type of floral clusters. Some like to harvest early when most of the pistils are still viable and at the height of reproductive potential. At this time the resins are very aromatic and light; the psychoactive effect is characterized as a light cerebral high (possibly low CBC and CBD, high THC, low CBN). Others harvest as late as possible, desiring a stronger, more resinous marijuana characterized by a more intense body effect and an inhibited cerebral effect (high CBC and CB]), high THC, high CBN). Harvesting and testing several floral clusters every few days over a period of several weeks gives the cultivator a set of samples at all stages of maturation and creates a basis for deciding when to harvest in future seasons. The following is a description of each of the growth phases as to morphology, terpene aroma, and relative psychoactivity.

Premature Floral Stage

At this stage floral development is slightly beyond primordial and only a few clusters of immature pistillate flowers appear at the tips of limbs in addition to the primordial pairs along the main stems. By this stage stem diameter within the floral clusters is very nearly maximum. The stems are easily visible between the nodes and form a strong framework to support future floral development. Larger vegetative leaves (5-7 leaflets) predominate and smaller tri-leaflet leaves are beginning to form in the new floral axis. A few narrow, tapered calyxes may be found nestled in the leaflets near the stem tips and the fresh pistils appear as thin, feathery, white filaments stretching to test the surroundings. During this stage the surface of the calyxes is lightly covered with fuzzy, hair-like, nonglandular trichomes, but only a few bulbous and capitatesessile glandular trichomes have begun to develop. Resin secretion is minimal, as indicated by small resin heads and few if any capitate-stalked, glandular trichomes. There is no bud yield from plants at the premature stage since THC production is low, and there is no economic value other than fiber and leaf. Terpene production starts as the glandular trichomes begin to secrete resin; premature floral clusters have no terpene aromas or tastes. Total cannabinoid production is low but simple cannabinoid phenotypes, based on relative amounts of THC and CBD, may be determined. By the pre-floral stage the plant has akeady established its basic chemotype as a fiber or bud strain. A fiber strain rarely produces more than 2% THC, even under perfect agricultural conditions. This indicates that a strain either produces some varying amount of THC (up to 13%) and little CBD and is termed a bud strain or produces practically no THC and high CBD and is termed a fiber strain, This is genetically controlled.

The floral clusters are barely psychoactive at this stage, and most marijuana smokers classify the reaction as more an “effect” than a “high.” This most likely results from small amounts of THC as well as trace amounts of CBC and CBD. CBD production begins when the seedling is very small. THC production also begins when the seedling is very small, if the plant originates from a marijuana strain. However, THC levels rarely exceed 2% until the early floral stage and rarely produce a “high” until the peak floral stage.

Early Floral Stage

Floral clusters begin to form as calyx production increases and internode length decreases. Tri-leaflet leaves are the predominant type and usually appear along the secondary floral stems within the individual clusters. Many pairs of calyxes appear along each secondary floral axis and each pair is subtended by a tri-leaflet leaf. Older pairs of calyxes visible along the primary floral axis during the premature stage now begin to swell, the pistils darken as they lose fertility, and some resin secretion is observed in trichomes along the veins of the calyx. The newly produced calyxes show few if any capitate-stalked trichomes. As a result of low resin production, only a slight terpene aroma and psychoactivity are detectable. The floral clusters are not ready for harvest at this point. Total cannabinoid production has increased markedly over the premature stage but THC levels (still less than 3%) are not high enough to produce more than a subtle effect.

Peak Floral Stage

Elongation growth of the main floral stem ceases at this stage, and floral clusters gain most of their size through the addition of more calyxes along the secondary stems until they cover the primary stem tips in an overlapping spiral. Small reduced mono-leaflet and tri-leaflet leaves subtend each pair of calyxes emerging from secondary stems within the floral clusters. These subtending leaves are correctly referred to as bracts. Outer leaves begin to wilt and turn yellow as the pistillate plant reaches its reproductive peak. In the primordial calyxes the pistils have turned brown; however, all but the oldest of the flowers are fertile and the floral clusters are white with many pairs of ripe pistils. Resin secretion is quite advanced in some of the older infertile calyxes, and the young pistillate calyxes are rapidly producing capitate-stalked glandular trichomes to protect the precious unfertilized ovule. Under wild conditions the pistillate plant would be starting to form seeds and the cycle would be drawing to a close. When Cannabis is grown for sinsemilla floral production, the cycle is interrupted. Pistillate plants remain unfertilized and begin to produce capitate -stalked trichomes and accumulate resins in a last effort to remain viable. Since capitate-stalked trichomes now predominate, resin and THC production increase. The elevated resin heads appear clear, since fresh resin is still being secreted, often being produced in the cellular head of the trichome. At this time THC acid production is at a peak and CBD acid levels remain stable as the molecules are rapidly converted to THC acids, THC acid synthesis has not been active long enough for a high level of CBN acid to build up from the degradation of THC acid by light and heat. Terpene production is also nearing a peak and the floral clusters are beautifully aromatic. Many cultivators prefer to pick some of their strains during this stage in order to produce marijuana with a clear, cerebral, psychoactive effect. It is believed that, in peak floral clusters, the low levels of CBD and CBN allow the high level of THC to act without their sedative effects. Also, little polymerization of resins has occurred, so aromas and tastes are often less resinous and tar like than at later stages. Many strains, if they are harvested in the peak floral stage, lack the completely developed aroma, taste and psychoactive level that appear after curing. Cultivators wait longer for the resins to mature if a different taste and psychoactive effect is desired.

This is the point of optimum harvest for some strains, since most additional calyx growth has ceased. However, a subsequent flush of new calyx growth may occur and the plant continue ripening into the late floral stage.

Late Floral Stage

By this stage plants are well past the main reproductive phase and their health has begun to decline. Many of the larger leaves have dropped off, and some of the small inner leaves begin to change color. Autumn colors (purple, orange, yellow, etc.) begin to appear in the older leaves and calyxes at this time; many of the pistils turn brown and begin to fall off. Only the last terminal pistils are still fertile and swollen calyxes predominate. Heavy layers of protective resin heads cover the calyxes and associated leaves. Production of additional capitate-stalked glandular trichomes is rare, although some existing trichomes may still be elongating and secreting resins. As the previously secreted resins mature, they change color. The polymerization of small terpene molecules (which make up most of the resin) produces long chains and a more viscous and darker-colored resin. The ripening and darkening of resins follows the peak of psychoactive cannabinoid synthesis and the transparent amber color of mature resin is usually indicative of high THC content. Many cultivators agree that transparent amber resins are a sign of high-quality Cannabis and many of the finest strains exhibit this characteristic. Particularly potent Cannabis from California, Hawaii, Thailand, Mexico, and Colombia is often encrusted with transparent amber colored instead of clear resin heads. This is also characteristic of Cannabis from other equatorial, subtropical and temperate zones where the growing season is long enough to accommodate long term resin production and maturation. Many areas of North America and Europe have too short a season to fully mature resins unless a greenhouse is used. Specially acclimatized strains are another possibility. They develop rapidly and begin maturing in time to ripen amber resins while the weather is still warm and dry.

The weight yield of floral clusters is usually highest at this point, but strains may begin to grow an excess of leaves in late-stage clusters to catch additional energy from the rapidly diminishing autumn sun. Total resin accumulation is highest at this stage, but the period of maximum resin production has passed. If climatic conditions are harsh, resins and cannabinoids will begin to decompose. As a result, resin yield may appear high even if many of the resin heads are missing or have begun to deteriorate and the overall psychoactivity of the resin has dropped. THC decomposes to CBN in the hot sun and will not remain intact or be replaced after the metabolic processes of the plant have ceased. Since cannabinoids are so sensitive to decomposition by sunlight, the higher psychoactivity of amber resins may be a secondary effect. It may be that the THC is better protected from the sun by amber or opaque resins than by clear resins. Some late maturing strains develop opaque, white resin heads as a result of terpene polymerization and THC decomposition. Opaque resin heads are usually a sign that the floral clusters are over-mature.

Late floral clusters exhibit the full potential of resin production, aromatic principles, and psychoactive effect. Complex mixtures of many mon oterpene and sesquiterpene hydrocarbons along with alcohols, ethers, esters, and ketones determine the aroma and flavor of mature Cannabis. The levels of the basic terpenes and their polymerized byproducts fluctuate as the resin ripens. The aromas of fresh floral clusters are usually preserved after drying, as by the late floral stage, a high proportion of ripe resins are present on the mature calyxes of the fresh plant. Cannabinoid production favors high THC acid and rising CBN acid content at this stage, since most active biosynthesis has ceased and more THC acid is being broken down into CBN acid than is being produced from CBD acid. CBD acid may accumulate because not enough energy is available to complete its conversion to THC acid. The THC-to-CBD ratio in the harvested floral clusters certainly begins to drop as biosynthesis slows, because THC acid levels decrease as it decomposes, and at the same time CBD acid levels remain or rise intact since CBD does not decompose as rapidly as THC acid. This tends to produce marijuana characterized by more somatic and sedative effects. Some cultivators prefer this to the more cerebral and clear psychoactivity of the peak floral stage.

Senescence or Rejuvenation Stage

After a pistillate plant finishes floral maturation, the production of pistillate calyxes ceases and the plant continues senescence (decline towards death). In unusual situations, however, rejuvenation will begin and the plant will sprout new vegetative growth in preparation for the following season. Senescence is often highlighted by striking color changes in the floral clusters. Leaves, calyxes, and stems display auxiliary pigments ranging in color from yellow through red to deep purple. Eventually a brown shade predominates and death is near. In warm areas, rejuvenation starts as vegetative shoots form within the floral clusters. These shoots are usually made up of unserrated single leaflets separated by thin stems with long internodes. It is as if the plant were reaching for limited winter light. Leaf production is accelerated as plants reach the rejuvenation stage, and resin production completely stopped. Floral clusters left to ripen until the bitter end usually produce inferior marijuana of lowered THC level, especially out doors in bad weather.

Terpene secretion changes along with cannabinoid secretion and psychoactive effect. Various terpenes, terpene polymers, and other aromatic principles are produced and ripen at different times in the development of the plant. If these changes in aromatic principles are directly correlated with changes in cannabinoid production, then harvest selections for cannabinoid level may be possible based on the aroma of the ripening floral clusters. It is important to understand differences in the anatomy of floral clusters for each Cannabis strain. Trends in the relative quantity (dry weight) of various parts (such as leaves, calyxes and trichomes) at various harvest dates are characteristic of particular strains and may vary widely. Some generalizations can be made. In most cases, the percentage of stem weight steadily decreases as the floral cluster matures. Rejuvenation growth can account for a sudden increase in stem percentage. The percentage of inner leaves usually starts very low and climbs rapidly as the floral clusters mature. This often reflects increased leaf growth near the end of the season. In many strains the percentage of inner leaves drops sharply during the peak floral stage and rises again as calyx production slows and leaf production in creases in the late floral stage.

Calyx production follows two basic patterns. In one, the percentage of calyxes climbs gradually and levels out during the peak floral stage. It begins to decline in the late floral stage, and leaf production increases as calyx production ceases. Other strains continue to produce calyxes at the expense of leaves, and the calyx percentage increases steadily throughout maturation. In both cases, there is some tendency for calyx percentage to level out during the peak floral stage irrespective of whether leaf growth accelerates or calyx growth continues at a later stage. Resins generally accumulate steadily while the plant matures, but strains may vary as to the stage of peak resin secretion. Seed percentage increases exponentially with time if the crop is well fertilized, but most samples of Cannabis grown domestically are nearly seedless. To determine dry weight, samples are harvested, labeled, and air dried until the central stem of the floral cluster will snap when bent. In plant research, dry weight is done in ovens at higher temperatures, but these higher temperatures would ruin the Cannabis. The dry floral cluster is weighed. The outer leaves, inner leaves, calyxes, seeds, and stems are segregated and each group weighed individually. The percentage is determined by dividing the individual dry weights by the total dry weight.

Calyx percentage ranges from 30 to 70% of the dry weight of the seedless floral clusters, depending on variety and harvest date. Inner leaf percentages fluctuate between 15 and 45% of dry weight; stems range from 10 to 30%. It seems obvious that for marijuana harvesting a maximum calyx production is important to quality resin production. A strain where maximum calyx production occurs simultaneously with peak resin production is a breeding goal not yet attained. Harvesting Cannabis at the proper time requires infor mation on how floral clusters mature and a decision on the part of the cultivator as to what type of floral clusters are desired. With harvesting as with other techniques of cultivation, the path to success is straightened when a definite goal is established. Personal preference is always the ultimate deciding factor.

Factors Influencing THC Production

Many factors influence the production of THC. In general, the older a plant, the greater its potential to produce THC. This is true, however, only if the plant remains healthy and vigorous, THC production requires the properquantity and quality of light. It seems that none of the biosynthetic processes operate efficiently when low light conditions prevent proper photosynthesis. Research has shown (Valle et al. 1978) that twice as much THC is produced under a 12-hour photoperiod than under a 10-hour photoperiod. Warm temperatures are known to promote metabolic activity and the production of THC. Heat also promotes resin secretion, possibly in response to the threat of floral desiccation by the hot sun, Resin collects in the heads of glandular trichomes and does not directly seal the pores of the calyx to prevent desiccation. Resin heads may serve to break up the rays of the sun so that fewer of them strike the leaf surface and raise the temperature. However, light and heat also destroy THC. In a bud strain, a biosynthetic rate must be maintained such that substantially more THC is produced than is broken down. Humidity is an interesting parameter of THC production and one of the least understood. Most high-quality Cannabis grows in areas that are dry much of the time at least during the maturation period. It follows that increased resin production in response to arid conditions might account for increased THC production. High-THC strains, however, also grow in very humid conditions (greenhouses and equatorial zones) and produce copious quantities of resin. Cannabis seems not to produce more resins in response to dry soil, as it does to a dry atmosphere. Drying out plants by with holding water for the last weeks of flowering does not stimulate THC production, although an arid atmosphere may do so. A Cannabis plant in flower requires water, so that nutrients are available. for operating the various biosynthetic pathways.

There is really no confirmed method of forcing increased THC production. Many techniques have developed through misinterpretations of ancient tradition. In Colombia, farmers girdle the stalk of the main stem, which cuts off the flow of water and nutrients between the roots and the shoots. This technique may not raise the final THC level, but it does cause rapid maturation and yellow gold coloration in the floral cluster (Partridge 1973). Impaling with nails, pine splinters, balls of opium, and stones are clandestine folk methods of promoting flowering, taste and THC production. However none of these have any valid documentation from the original culture or scientific basis. Symbiotic relationships between herbs in companion plant ings are known to influence the production of essential oils. Experiments might be carried out with different herbs, such as stinging nettles, as companion plants for Cannabis, in an effort to stimulate resin production. In the future, agricultural techniques may be discovered which specifically promote THC biosynthesis.

In general, it is considered most important that the plant be healthy for it to produce high THC levels. The genotype of the plant, a result of seed selection, is the primary factor which determines the THC levels. After that, the provision of adequate organic nutrients, water, sunlight, fresh air, growing space, and time for maturation seems to be the key to producing high-THC Cannabis in all circumstances. Stress resulting from inadequacies in the environment limits the true expression of phenotype and cannabinoid potential. Cannabis finds a normal adaptive defense in the production of THC laden resins, and it seems logical that a healthy plant is best able to raise this defense. Forcing plants to produce is a perverse ideal and alien to the principles of organic agriculture. Plants are not machines that can be worked faster and harder to produce more. The life processes of the plant rely on delicate natural balances aimed at the ultimate survival of the plant until it reproduces. The most a Cannabis cultivator or researcher can expect to do is provide all the requisites for healthy growth and guide the plant until it matures.

Flowering in Cannabis may be forced or accelerated by many different techniques. This does not mean that THC production is forced, only that the time before and during flowering is shortened and flowers are produced rapidly. Most techniques involve the deprivation of light during the long days of summer to promote early floral induction and sexual differentiation. This is sometimes done by moving the plants inside a completely dark structure for 12 hours of each 24-hour day until the floral clusters are mature. This stimulates an autumn light cycle and promotes flowering at any time of the year. In the field, covers may be made to block out the sun for a few hours at sunrise or sunset, and these are used to cover small plants. Photoperiod alteration is most easily accomplished in a greenhouse, where blackout curtains are easily rolled over the plants. Drug Cannabis production requires 11-12 hours of continuous darkness to induce flowering and at least 10 hours of light for adequate THC production (Valle et al. 1978). In a greenhouse, supplemental lighting need be used only to extend daylength, while the sun supplies the energy needed for growth and THC biosynthesis. It is not known why at least 10 hours (and preferably 12 or 13 hours) of light are needed for high THC production. This is not dependent on accumulated solar energy since light responses can be activated and THC production increased with only a 40-watt bulb. A reasonable theory is that a light-sensitive pigment in the plant (possibly phytochrome) acts as a switch, causing the plant to follow the flowering cycle. THC production is probably associated with the induction of flowering resulting from the photoperiod change.

Cool night temperatures seem to promote flowering in plants that have previously differentiated sexually. Extended cold periods, however, cause metabolic processes to slow and maturation to cease. Most temperate Cannabis strains are sensitive to many of the signs of an approaching fall season and respond by beginning to flower. In contrast, strains from tropical areas, such as Thailand, often seem unresponsive to any signs of fall and never speed up development.

Contrary to popular thought, planting Cannabis strains later in the season in temperate latitudes may actually promote earlier flowering. Most cultivators believe that planting early gives the plant plenty of time to flower and it will finish earlier. This is often not true. Seedlings started in February or March grow for 4-5 months of increasing photoperiod before the days begin to get shorter following the solstice in June. Huge vegetative plants grow and may form floral inhibitors during the months of long photoperiod. When the days begin to get shorter, these older plants may be reluctant to flower because of the floral inhibitors formed in the pre-floral leaves. Since floral cluster formation takes 6-10 weeks, the initial delay in flowering could push the harvest date into November or December. Cannabis started during the short days of December or January will often differentiate sex by March or April. Usually these plants form few floral clusters and rejuvenate for the long season ahead. No increased potency has been noticed in old rejuvenated plants. Plants started in late June or early July, after the summer solstice, are exposed only to days of decreasing photoperiod. When old enough they begin flowering immediately, possibly because they haven’t built up as many long-day floral inhibitors. They begin the 6-10 week floral period with plenty of time to finish during the warmer days of October. These later plantings yield smaller plants because they have a shorter vegetative cycle. This may prove an advantage. in green house research, where it is common for plants to grow far too large for easy handling before they begin to flower. Late plantings after the summer solstice receive short inductive photoperiods almost immediately. However, flowering is delayed into September since the plant must grow before it is old enough to flower. Although flowering is delayed, the small plants rapidly produce copious quantities of flowers in a final effort to reproduce.

Extremes in nutrient concentrations are considered influential in both the sex determination and floral development of Cannabis. High nitrogen levels in the soil during the seedling stage seem to favor pistillate plants, but high nitrogen levels during flowering often result in delayed maturation and excessive leafing in the floral clusters. Phosphorus and potassium are both vital to the floral maturation of Cannabis. High-phosphorus fertilizers known as “bloom boosters” are available, and these have been shown to accelerate flowering in some plants. However, Cannabis plants are easily burned with high phosphorus fertilizers since they are usually very acidic. A safer method for the plant is the use of natural phosphorus sources, such as colloidal phosphate, rock phosphate, or bone meal; these tend to cause less shock in the maturing plant. They are a source of phosphorus that is readily available as well as long-term in effect. Chemical fertilizers sometimes produce floral clusters with a metallic, salty flavor. Extremes in nutrient levels usually affect the growth of the entire plant in an adverse way.

Hormones, such as gibberellic acid, ethylene, cytokinins and auxins, are readily available and can produce some strange effects. They can stimulate flowering in some cases, but they also stimulate sex reversal. Plant physiology is not simple, and results are usually unpredictable.

Harvesting, Drying, and Curing

Cannabis is cultivated for the harvest of several different commercial products. Pulp, fiber, seed, buds, and resin are produced from various parts of the Cannabis plant. The methods of harvesting, drying, curing, and storing various plant parts are determined by the intended use of the plant. Pulp is made from the leaves of juvenile plants and from waste products of fiber and bud production. Fibers are produced from the stems of the Cannabis plant. The floral clusters are responsible for the production of seeds, buds, and aromatic resins.

If plants are to be used solely as a pulp source for paper production, they may be harvested at any point in the life cycle when they are large enough to produce a reasonable yield of leaves and small stems. The leaves and small stems are stripped from the larger stalks, and after drying they are bailed and stored or made directly into paper pulp. Cannabis contains approximately 67% cellulose and 16% hemicellulose; this makes a fine resilient paper. In Italy, the finest Bibles are printed on hemp paper.

Fiber or hemp Cannabis is usually grown in large, crowded fields. Crowding of seedlings results in tall, thin plants with few limbs and long, straight fibers. The total field is harvested when the fiber content reaches the correct level but before the fibers begin to lignify or harden. The cut stalks are stripped of leaves and bundled to dry. Fibers are extracted by natural or chemical retting, Retting is the breaking down of the outside skin layer and tissues that join the fibers into bundles, so that the individual fibers are freed. Natural retting is accomplished by soaking the stalks in water and laying them out on the ground, where they are attacked by decay organisms such as fungi and bacteria. Dew may also wet the stalks, and they are turned frequently to evenly wet them and avoid excessive decay. Continued soaking, attack by organisms, and pounding of the stalks results in the liberation of individual fibers from their vascular bundles. Natural retting takes from one week to a month. The fibers are thoroughly dried, wrapped in bundles and stored in a cool, dry area. The yield of fiber is approximately 25% of the weight of the dried stalks.

Seeds are harvested by cutting fields of seeded pistillate plants and removing the seeds either by hand or machine. Cannabis seeds usually fall easily from the floral clusters when mature. The remainder of the plant may be used as pulp material or low-grade marijuana. The Indian tradition of preparing ganja is by walking on it and rolling it between the palms to remove excess seeds and leaves. Seeds are allowed to dry completely and all vegetable debris is removed before storage. This prevents spoilage caused by molds and other fungi. Seeds to be used for oil production may be stored in bags, boxes, or jars, and not exposed to excess humidity (causing them to germinate) or excessive aridity (causing them to dry out and crack). Seeds preserved for future germination are thoroughly air dried in paper envelopes or cloth sacks and stored in airtight containers in a cool, dark, dry place. Freezing may also dry out seeds and cause them to crack. If seeds are carefully stored, they remain viable for a number of years. As a batch of seeds ages, fewer and fewer of them will germmate, but even after 5 to 6 years a small percentage of the seeds usually still germinate. Old batches of seeds also tend to germinate slowly (up to 5 weeks). This means that a batch of seeds for cultivation might be stored for a longer time if the initial sample is large enough to provide sufficient seeds for another generation. If a strain is to be preserved, it is necessary to grow and reproduce it every three years, so that enough viable seeds are always available.

Curing Floral Clusters

Harvesting, drying, curing, and storage of Cannabis floral clusters to preserve and enhance appearance, taste, and psychoactivity is often discussed among cultivators. More floral clusters are ruined by poor handling after harvest than by any other single cause. When the plant is harvested, the production of fine floral clusters for smoking begins. Cannabis floral clusters are harvested by two basic methods: either individually, by cutting them from the stalks and carefully packaging them in shallow boxes or trays, or all simultaneously by uprooting or cutting off the entire plant. In instances where the floral clusters mature sequentially, individual harvest is used because the entire plant is not ripe at any given time. Removing individual clusters also makes drying easier and quicker because the stalks are divided into shorter pieces. Floral clusters will dry much more slowly if the plant is dried whole. This means that all of the water in the plant must pass through the stomata on the surface of the leaves and calyxes instead of through cut stem ends. The stomata close soon after harvest and drying is slowed since little water vapor escapes.

Boiling attached Cannabis roots after harvesting whole plants, but before drying, is an interesting technique. Originally it was thought by cultivators that boiling the roots would force resins to the floral clusters. In actuality, there are very few resins within the vascular system of the plant and most of the resins have been secreted in the heads of glandular trichomes. Once resins are secreted they are no longer water-soluble and are not part of the vascular system. As a result, neither boiling nor any other process will move resins and cannabinoids around the plant. However, boiling the roots does lengthen the drying time of the whole plant. Boiling the roots shocks the stomata of the leaves and forces them to close immediately; less water vapor is allowed to escape and the floral clusters dry more slowly. If the leaves are left intact when drying, the water evaporates through the leaves instead of through the flowers.

Whole plants, limbs, and floral clusters are usually hung upside down or laid out on screen trays to dry. Many cultivators believe that hanging floral clusters upside-down to dry makes the resins flow by gravity to the limb tips. As with boiling roots, little if any transport of cannabinoids and resins through the vascular system occurs after the plant is harvested. Inverted drying does cause the leaves to hang next to the floral clusters as they dry, and the resins are protected from rubbing off during handling. Floral clusters also appear more attractive and larger if they are hung to dry. When laid out flat to dry, floral clusters usually develop a flattened, slightly pressed profile, and the leaves do not dry around the floral clusters and protect them. Also, the floral clusters are usually turned to prevent spoilage; this requires extra handling. It is easy to bruise the clusters during handling, and upon drying, bruised tissue will turn dark green or brown. Resins are very fragile and fall from the outside of the calyx if shaken. The less handling the floral clusters receive the better they look, taste and smoke. Floral clusters, including large leaves and stems, usually dry to about 25% of their original fresh weight. When dry enough to store without the threat of mold, the central stem of the floral cluster will snap briskly when bent. Usually about 10% water remains in dry, stored Cannabis floral clusters prepared for smoking. If some water content is not maintained, the resins will lose potency and the clusters will disintegrate into a useless powder exposed to decomposition by the atmosphere.

As floral clusters dry, and even after they are sealed and packaged, they continue to cure. Curing removes the unpleasant green taste and allows the resins and cannabinoids to finish ripening. Drying is merely the removal of water from the floral clusters so they will be dry enough to burn. Curing takes this process one step farther to produce tasty and psychoactive marijuana. If drying occurs too rapidly, the green taste will be sealed into the tissues and may remain there indefinitely. A floral cluster is not dead after harvest any more than an apple is. Certain metabolic activities take place for some time, much like the ripening and eventual spoiling of an apple after it is picked. During this period, cannabinoid acids decarboxylate into the psychoactive cannabinoids and terpenes isomerize to create new polyterpenes with tastes and aromas different from fresh floral clusters. It is suspected that cannabinoid biosynthesis may also continue for a short time after harvest. Taste and aroma also improve as chlorophylls and other pigments begin to break down. When floral clusters are dried slowly they are kept at a humidity very near that of the inside of the stomata. Alternatively, sealing and opening bags or jars or clusters is a procedure that keeps the humidity high within the container and allows the periodic venting of gases given off during curing. It also exposes the clusters to fresh air needed for proper curing. If the container is airtight and not vented, then rot from anaerobic bacteria and mold is often seen. Paper boxes breathe air but also retain moisture and are often used for curing Cannabis. Dry floral clusters are usually trimmed of outer leaves just prior to smoking. This is called manicuring. The leaves act as a wrapper to protect the delicate floral clusters. If manicured before drying, a significant increase in the rate of THC breakdown occurs.


Cannabis floral clusters are best stored in a cool, dark place. Refrigeration will retard the breakdown of cannabinoids, but freezing has adverse effects. Freezing forces moisture to the surface from the inside of the floral tissues and this may harm the resins secreted on the surface. Floral clusters with the shade leaves intact are well protected from abrasion and accidental removal of resins, but manicured floral clusters are best tightly packed so they do not rub together. Glass jars and plastic freezer bags are the most common containers for the storage of floral clusters. Polyethylene plastic sandwich or trash bags are not suited to long-term storage since they breathe air and water vapor. This may cause the floral clusters to dry out excessively and lose potency. Heat-sealed boilable plastic pouches do not breathe and are frequently used for storage. Glass canning jars are also very air-tight, but glass breaks. It is feared by some connoisseurs that plastic may also impart an unpleasant taste to the floral clusters. In either case, additional care is usually taken to protect the floral clusters from light so another opaque container is used to cover the clear glass or plastic wrapping. Clusters are not sealed permanently until they have finished curing. Curing involves the presence of oxygen, and sealing floral clusters will end the free exchange of oxygen and end curing. However, oxygen also causes the slow breakdown of THC to CBN, so after the curing process is completed, the container is completely sealed. Any oxygen present in the container will be used up and no more can enter. Nitrogen has been suggested as a packing medium because it is very nonreactive and inexpensive. Jars or bags may be flooded with nitrogen to displace air and then sealed. Vacuum-sealing machines are available for Mason jars and may be modified to vacuum-sealed bags.

The proper harvesting, curing, and storage of Cannabis closes the season and completes’ the life cycle. Cannabis is certainly a plant of great economic potential and scientific interest; its rich genetic diversity deserves preservation and its possible beneficial uses deserve more research.

4 comments to Marijuana Botany – Cannabis Maturation and Harvesting

  • greenfinger

    well written and worthy of praise. Nice job. Each cultivator have their own criteria based upon their specific growing zone. This article is concise and broadly applicable. Thanks

  • David Turner

    my plant has stopped in the middle of flower!!!! It started flower in april, mostly white/clear pistol hairs, lighting is 12/12 humidity and temp are acceptable lights no change

  • Bill

    I’m wondering if this is a miss print – isn’t the pole at 90 degrees latitude?:
    “At 200 latitude, the photoperiod never exceeds 14 hours, and easily induced strains may begin flowering at nearly any time during the year.”

    • kgb

      I think you are right. I double checked the source and it does say “200 north latitude” a few times, but I think it was meant to be “20” instead. I will look into it, and correct it if needed. Thanks!

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