Soil pH Facts

How does pH level affects the growth of a marijuana plant

The pH levels within a plant will directly affect a marijuana plant’s growth as well as nutrient availability. The pH levels can also affect a plant’s ability to absorb nutrients through its roots. PH levels that rise above 7.5 will cause manganese [Mn], boron [B], copper [C], iron [Fe], and Zinc [Zn] ions to become less abundant for the marijuana plant. PH values that fall before 6 will cause solubility issues for phosphoric acid, magnesium [Mg], and calcium [Ca]. PH values that range between 3 and 5 promote the development of numerous fungal diseases when paired with temperatures above approximately 79°F (26°C).

Why pH can vary

The ratio of uptake in anions and cations [which are the negatively and positively changed nutrients respectively] by your marijuana plants might cause a substantial shift in pH. Generally, an excessive amount of cations over anions, will lead to decreases in your pH, where as any excess in anion over cation will lead to a spike in the pH. Nitrogen [N] [which is required in large doses for healthy plant growth] might be supplied as either cation or anion in nutrient solutions and may have drastic effects on the rate direction and rate in which the pH changes. This shift in pH can happen remarkably fast, making it difficult to monitor and adjust correctly. Photosynthesis produces ions made of hydrogen, causing nutrient acidity to spike [dropping the pH]. Once the sun goes down and the photosynthesis stops, cannabis plants will increase their respiration rate. The respiration of various micro-organisms as well as the decomposition of any and all organic matter will consume the hydrogen ions causing the acidity of your solution to decrease [pH rises]. Most strains of marijuana grow the best in a nutrient rich solution with a pH within the range of 6.0 and 7.5, as well as an environmental temperature between 68°F and 71°F (20°C and 22°C). Indoor plants [or plants grown outdoors, and encounter heavy overcast] will absorb more phosphorous [P] and potassium [K] from nutrient solutions causing the acidity to rise [pH drops].

The two ways of controlling pH

Extreme levels in pH may result in precipitation of specific nutrients. Marijuana roots will still be able to absorb these nutrients but they have to be dissolved in a solution. This precipitation process [the opposite of dissolving] will result in the solution clumping or forming solids within it, thus making it impossible for the plants to get the nutrients they need. Not all of the precipitation will settle at the bottom of your tanks, some may occur as very small suspension, which is invisible to the human eye. Often times, marijuana plants will tell us these problems through changes in their leaves, typically when it is too late to be fixed. Iron is one of the essential nutrients that marijuana plants require, who’s solubility is directly affected by the pH. This is why iron is added daily as a chelated form. When your pH value is greater than 7, less than half of the iron that the marijuana plant needs is available. Once the pH level reaches 8, there is no iron within the solution thanks to iron hydroxide precipitation, which over time will transform into rust. If you are able to keep your pH level below 6.5, more than 90 percent of your iron will become available for the plants. If you vary the pH of your nutrient solutions you can change the solubility of the phosphorus and calcium. When your pH levels are above 6.0 the amount of calcium and phosphorus that is available for your marijuana plants decrease. Poor quality water may also increase various precipitation reactions, which is why it is important to use fresh, clean water for your solutions. If you can maintain a pH balance between the range of 4.0 and 6.0, virtually all essential nutrients will become available to your plants.

Adjusting pH

The addition of alkalis or acids to your nutrient solution is perhaps the most practical means to adjust your pH, and can be automated rather easily. You can also find several different ways to minimize your pH variations and are worth serious consideration. Nitrogen is the single largest quantity inorganic nutrient required by marijuana plants. Most species of marijuana plants are capable of absorbing both nitrate and ammonium as their sole source of nitrogen. Some types of plants will yield better if they are supplied with a mixture of nitrate and ammonium when compared to using just nitrate alone. This combination may also be used as a buffer against constantly changing pH levels. Marijuana plants that are grown in a nitrate solution for its nitrogen requirements tend to increase the pH level of the solution, thus requiring the addition of acids into the solution. When 10 to 20 percent of the nitrogen is provided in the form of ammonium, your nutrient solution will stabilize around a 5.5 pH level. Ammonium concentrations will need to be closely monitored since it has been proven that micro-organisms that grow on the plant roots will convert ammonium to nitrates. It is now possible to accurately monitor these levels through the use of a hand-held ion-selective device. You can find two different forms of fertilizers that contain both phosphorus and potassium. Equal parts of both potassium and phosphorus can be used to easily maintain the pH level at approximately 7.0.

A buffer is a solution which can resist the pH change and can be used to calibrate your pH electrodes. Buffers can also be added into your nutrient solutions to help maintain a stable pH level. An example of one of these buffers is called 2 [N morpholino] ethanesulfronic acid, which is commonly called MES. A large number of companies that claim better control over pH levels through use of their ‘specially’ formulated solutions, add MES into the mixtures. It is important to bare in mind that whenever using an MES based product that your pH level will be low and requires adjusting through the use of an alkali, to bring the pH back to your required level. You can also use chelating resins and ion-exchanges to stabilize the pH. Generally speaking, these resins are produced as small beads that have the nutrients already absorbed or chelated into them. As your marijuana plants begin to absorb the nutrients, the resins activate and release even more nutrients. The goal is to obtain a controlled release of these nutrients into the solution in hopes of mimicking the way your growing soils would release the nutrients. In an ideal setting these nutrient releases will be able to adequately supply your growing plants with the nutritional demands of the plant while maintaining a stable pH.

Is the adjustment of pH critical?

The pH level is not as crucial as most hydroponic growers believe it is. The goal is to try and avoid the extreme levels of pH on either side of the scale. Marijuana plants are grown in soils with a wider range of pH levels than most hydroponically grown plants. Most plant species have an optimum pH level within the range of 5.0 to 6.0.

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