What’s pH? This is a question that usually makes new growers scratch their heads and reach for the pipe. The term pH refers to the level of alkalinity or acidity of a liquid substance. The pH scale starts at 0 and rises to 14. A value of 7.0 is considered neutral, with values over 7.0 being alkaline and values below 7.0 being acidic. The liquid is the nutrient solution being used to grow a healthy cannabis plant.
The nutrient solution is basically a cocktail of various chemicals. These chemicals can react to each other in a process called covalent bonding and form new chemicals that the plant can’t effectively use. This process of covalent bonding is largely dependent on the pH of the solution the chemicals are suspended in, in this case water. With the chemicals being used in the average hydroponic solution, a chemist would say that the optimum pH would be 7.0, which is neutral. In keeping the solution neutral, covalent bonding of the constituent parts of the solution will be kept to a minimum.
However, since cannabis plants like a different pH level for optimum growth, it’s okay to lower the pH and take the slight loss of nutrient value. Fast growing, leafy plants generally like a lower pH in the range of 5.2 to 5.9. Fortunately, a lower pH will bond fewer nutrients than a higher pH will. If the pH value goes beyond the optimum range of 5.2 to 5.9, undesirable levels of nutritional deficiency and toxicity will occur, both of which can seriously impede plant growth. Be vigilant.
In researching the various hydroponic methods in use, most of the growing media like rockwool, pea gravel and sand is relatively inert. That means the growing medium won’t react with the nutrients in the solution. For those methods that use inert media, a pH of 5.2 is recommended for optimal elemental uptake. It is at this pH level that the roots will assimilate the nutrients in the solution most efficiently. If the root has to work less to assimilate the required nutrients, the rest of the plant will benefit.
Measuring and Adjusting pH
Measuring pH is relatively easy and there are quite a few choices in terms of methods. The most inexpensive and low-tech method for measuring just requires purchasing a pH kit and taking a sample from the nutrient solution. After following the directions, use the color chart to determine the pH of the solution.
This low-tech solution poses some obvious limitations, not the least of which is the difficulty in deciding which color is closest if you’ve been into the fruits of your previous harvest. The kits typically sell for $5 to $10.
If the pH isn’t the appropriate level for your plant, knowing what chemical to add to the nutrient solution and when is paramount to success as a grower. When the pH level is alkaline, meaning the pH level is above seven, it can be lowered with saltpeter, sulfuric acid or phosphorous. When the pH value is too low, it can be raised with calcium carbonate, lime or potash. Most fertilizers cause a pH change in the nutrient solution. Adding fertilizer to the nutrient solution almost always results in a more acidic pH, so adjust accordingly.
Handling all of these chemicals safely is important. As a general rule, never use metal. Instead opt for glass or plastic or the nutrients will react with the elements in the metal and mess up the nutrient ratios. Never add the acid to the vat of nutrient. Fill a small glass container with the nutrient to be balanced and add a few drops of the necessary chemical. Stir it in well and add small amounts at a time to the large vat of nutrient until the proper pH balance is achieved.
As time goes on, the amount of salts produced by the breakdown of fertilizers in the medium causes it to become increasingly acidic. Eventually, the concentration of these salts in the medium will stunt the plant and cause browning out of the foliage. As the plant gets older, its roots become less effective in bringing food to the leaves. To avoid the accumulation of these salts in the medium and to ensure that the plant is getting all of the food it needs, be sure to flush the system with clean, pH-balanced water every couple of weeks. Do this in lieu of that cycle’s feeding.
There’s always been a big debate over when to adjust your pH – before and after you add nutrients to the water, or just after. The truth is, growers can do both. The reasoning for doing both is that water is rarely dead on neutral. It’s either acidic or alkaline, depending on the region. Render the water neutral first by bringing it to a pH of 7.0. Then add the nutrients to that chemically-neutral solution and adjust to the desired range within 5.2 to 5.9 pH.
Because there are so many factors that go into the delicate art of cultivating cannabis, learning how to properly measure and adjust the pH balance on nutrient solutions will have a clear effect on the appearance, potency and health of cannabis plants. Practicing and perfecting this step will be what makes a grower’s crop stand out from the crowd.
TELL US, have you taken pH into consideration when growing cannabis plants?