“Incorrect pH belongs to the most serious nutrient disorders in organic-soil gardens. Many complex biological processes occur between organic fertilizers and the soil during nutrient uptake. The pH is critical to the livelihood of these activities.” (Marijuana Horticulture, Jorge Cervantes)
- single nutrient deficiency or multiple nutrient deficiencies causing any of the following: stunted growth, yellowing, dark blotches on leaves, small dark-blue leaves, contorted shoots, shriveled growth, leaf curl or burn, leaf drop, delayed flowering, low yield, etc.
- higher ratio of males during sexing
- appearance of male flowers on females
- vulnerability to mold and fungus
- vulnerability to pests
Cannabis requires a pH range around the neutral value of 6.0-6.5 so that it can assimilate nutrients from the growing medium. In any cultivation the pH of the water must therefore be monitored and adjusted appropriately. A full point difference in pH represents a tenfold increase in either acidity or alkalinity. If you water on soil with pH 5.5 it is 10 times more acidic than pH 6.5! A pH below 6.0 can trigger a deficiency of calcium resulting in burnt root tips and black spots on leaves. A pH above 7.0 causes a deficiency in iron which results in chlorotic leaves and yellowing of veins. The assimilation of all major & secondary nutrients required by cannabis for healthy growth and flowering can be seriously affected by an incorrect pH. Most affected are phosphorous, potassium, magnesium, calcium, iron, and manganese. Read our Nutrient Problems Guide for more info on symptoms.
Photo: a standard pH kit for hydroponics includes a liquid pH tester, pH UP (potassium) and pH DOWN (nitric or phosphoric acid) for adjusting the pH range. Alternatively, vinegar can be used on some growing mediums to reduce pH if mineral salts are undesirable due to their effect on the EC of the nutrient solution.
Purchase your essential gardening kit.
In the world of plants each plant species is perfectly adapted to a certain pH range of the soil or water. Hobby gardeners are usually familiar with the different pH requirements of various plants like rhododendron, roses, or conifers, and buy special soil mixes and regulate the pH of water appropriately.
Add the required nutrients to your water until you have the appropriate EC (nutrient concentration) for your plants.
Measure the pH of the nutrient solution.
If the pH is still too high add vinegar * or pH DOWN until the solution has the correct pH.
If the pH is too low add pH UP until the solution has the correct pH.
When you are using tap water let it sit in a container for a few hours so that the chlorine evaporates.
Your municipal water board can provide a free chemical analysis of the tap water in your neighbourhood if you request it because they regularly perform these tests as a standard procedure. Usually this is not necessary for you to look into unless the water is very poor quality or running through old pipes that pose a health hazard.
Photo: this is a standard colour chart for a liquid pH tester. The optimum pH range of water for cannabis cultivation in soil is a light green colour that indicates pH 6.2-6.5
Wasser und pH The pH is the measure of the acidity or alkalinity of a solution or substrate. A low pH shows that the solution is acidic and a high pH that it is base/alkaline. The middle value