Marijuana Quality and Yield

by Ed Rosenthal

Yield is the obsession of many gardeners. How much will a plant produce ? That may seem like a simple question, but there are many facets. For indoor gardeners, space, watts, and time are considerations. For outdoor gardeners space, shape, and ripening time are of concern. Raw numbers don’t tell the whole story. Quality is also a factor. Less herb with better qualities is often preferable to more mediocre stash.

Indoor gardeners often refer to yield per watt. A half-gram to gram per watt of light is a good average expectation, but maturation time must also be taken into account. If a variety requires 90 days to mature, delivering a gram per watt, it has required 50% more flowering time than the variety that ripen in 60 days.

Why choose a late ripening variety ? Most gardeners choose what to cultivate for its essence: it approximates the ideal of the effects they desire or think are desireable; basically, it is herb leads in directions they want to grow.

marijuana garden

Yield is determined by both genetic and environmental factors. The genes set the potential, the blueprint for its life plan. The environment determines how well the plant’s needs are met and thus how close it will come to its genetic potential.

The plant’s growth pattern, flowering and ripening time, bud size, quality, odor, taste and high are all genetically programmed. Similar to grapes made into wines, all samples of a particular variety will have a somewhat similar flavor. However, plants of the same genetic stock produce their own unique flavors when grown in different places or under different conditions. The interplay between genetics and environment results in the unique qualities of each harvest.

The best way to assure high yield of superior produce is to plant the best varieties adapted to the environment you are using. An adapted variety will perform closer to its potential. Plants that may have to adapt to unsuitable environments may struggle and perform below expectations.

So what are the environmental factors that influence plant growth ? The main ones are light, nutrients, temperature, water and CO2. Each of these plays a role in plant growth: control them and you are on the road to producing the finest flowers.


Plants use light to fuel photosynthesis. This process creates sugar, which is used for energy and tissue building. You could say that light equals growth. The more light the plant receives, the more sugar is available for tissue growth. Plants growing under otherwise identical conditions will produce more tissue growth when more intense light per square foot is provided, so long as temperature remains in the acceptable range. A plant in full sun produces more – and better quality – than one in part shade. UV light plays a role in THC production. As the UV-B spectrum intensifies, THC content of quality strains will also rise. Plants cultivated at higher altitudes or harvested during mid-summer have higher THC content than low altitude or fall-ripened plants.


To function and grow, plants need nutrients. Their needs change as the plant moves through its life cycle. Nitrogen, phosphorus and potassium are the building blocks, and can be seen on fertilizer labels in the abbreviation N-P-K. When plants are denied a balanced supply of nutrients, their growth is impeded. Plants tell you what they need, you just have to understand their landuage. Every deficiency and toxicity condition has readily identifiable symptoms. Just read a good grow book, or a few, to learn the language of the leaves.


Indoors and out, plants do best at moderate temperature, in the mid-70s F (low 20s C). When the temps drop below that, growth suffers because metabolism slows down. At higher temps, the buds and flowers become misshapen and stretch. Of course, varieties differ in their preferences and tolerances to heat and coolness.


Indoors, water quantity is usually not a concern, but sometimes water quality can be a problem.Outdoors, nature can be too stingy or too generowus with her watering program. This impacts yield. However, some of the impact can be mitigated by preparing your garden for the unexpected drought and finding out about water quality.

Carbon Dioxide (CO2)

During photosynthesis, plants combine CO2 with water to form sugar. The amount of C)2 in the air influences the rate of photosynthesis. The atmosphere typically contains a concentration of CO2 at about 375 parts per million (ppm). As the level drifts down to 200 ppm, photosynthesis gradually grinds to a halt. When air is enriched with CO2 (and there is sufficient light), the photosynthesis rate rises, more sugar is produced, and plants grow bigger, faster, and produce more flowers. Enriching indoor gardens with CO2 is the cheapest environmental method of increasing yield and shortening ripening time.

1 comment to Marijuana Quality and Yield

  • Bill C.

    Hey Ed,
    I’m involved with a recreational cannabis biz here in E. Washington State.
    I’m trying to find info on what the best quality cannabis is, indoor grown or outdoor grown. Seems many people believe, indoor grown to be the best quality.
    I’ve been growing the same strains both indoors and outdoors for many years now. Personally, from my experiences with these two different growing situations, I much prefer outdoor grown to indoor grown, in most all aspects. I feel outdoor/sun grown, tastes better, it smells better, outdoor may not have quite as pungent of smell as indoors. Sun grown buds are defiantly bigger, the buds seem to be less leafy and much more dense then indoor grown. Then the big issue. It sure seems to me, outdoor grown cannabis is every bit as potent as indoor. That’s IF the plants were grown properly and were allowed to fully mature outdoors. Then there’s the fact that Sun Grown cannabis is all NATURAL, it’s not a semi artificial product like indoor grown is. Anyway, I’m just curious as to what your thoughts are on the outdoor verses indoor?

    BTW. I purchased you first book on growing back around 1980 or so. Thank you for that. It got me to where I am today!

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