How to Adjust pH Levels to Grow Marijuana Plants

Growing marijuana requires strict attention to certain parameters; and one of the most critical factors is the pH (or acidity level) of both one’s growing medium and their irrigation water, as this directly affects the nutrients available to the plant, and is crucial for optimal growth.

The pH (potential hydrogen) of a solution reflects its acidity or alkalinity and indicates the presence of hydrogen ions in the solution, which can significantly affect plants because it influences nutrient uptake, cellular respiration, enzyme activity and a number of other metabolic processes. If the pH is too high or too low, nutrients will bind to other compounds and become unavailable for roots, leaching from the soil.

On a scale, pH values range from 0 and 14: a solution with a pH value of 7 is considered neutral, numbers below 7 indicate an acidic substance, and numbers above 7 indicate an alkaline substance. It should be noted that the pH scale uses the common logarithm (that is, with base 10), such that slight numerical fluctuations entail large differences in practice. For example, water with a pH of 6.0 is ten times more acidic than water with a pH of 7.0.

How pH affects marijuana plants’ growth

For cannabis plants, the pH of the growing medium or nutrient solution should, ideally, be between 6.0 and 7.0. If pH levels are too low, the medium will be too acidic and the plant will not be able to absorb certain nutrients, such as phosphorus and potassium. Low pH levels can also increase the solubility of other nutrients (such as calcium and magnesium), which can cause toxicity.

Conversely, if pH levels are too high, the growing medium will be too alkaline, and the plant will not be able to utilize other specific nutrients, such as iron and zinc, both of which can lead to stunted growth and lower yields.

Cannabis can regulate micronutrient intake with pH ranges as wide as 5.0 to 7.0, but expert growers recommend keeping the pH in a narrower range, from 5.5 to 6.5, or even 5.8 to 6.2. In addition, the ideal pH range varies slightly between the vegetative and flowering phases. For example, ideal ranges would be:

• Seedling stage :       5.6-5.9
• Vegetative stage : 5.7-5.9
• Early flowering :        6.0-6.2
• Late flowering :        6.0-6.3

How to measure the pH of a cannabis crop

There are three main types of pH test:

• The least expensive ones come in strips or paper, but they are also the least effective. Their color changes according to pH levels.
• Another type includes probes, or rods. These are the most popular; you simply insert the probe into the solution to check pH levels.
• Finally, electronic or digital pH meters are the most expensive option, but provide more accurate and easier-to-read results.

How to modify the pH of a marijuana crop

If you want to adjust pH values to benefit your cannabis plants, you have two options: you can increase or decrease the pH of the substrate, but you can only do this before planting the marijuana seeds. If the plants are already growing, you can only adjust the pH values by changing the acidity level of the irrigation water.

Adjusting the substrate’s pH

The easiest way to adjust pH is through the use of natural products including manure, worm castings, compost, compost tea, lemon juice, vinegar, lime, limestone, pine needles or wood chips. For example, dolomite lime can be added to raise the pH if it is too low, while sulfur can be added to lower pH if it is too high.

Adjusting the water’s pH

By adjusting the pH of your irrigation water, you will also adjust the pH value of the soil where the water ends up. Lower the pH by adding peat moss or phosphoric acid. If the pH is too low, you can raise it by adding lime, baking soda or wood ashes.

Adjustment with chemicals

Apart from organic products, you can also use chemical agents. These products, called pH Up and pH Down, are available in liquid form at any gardening center, and take effect quickly.

Regularly testing and adjusting pH levels, as needed, is a fundamental part of growing marijuana. By maintaining proper pH levels, growers can look forward to strong, productive plants and boost their yields of high-quality cannabis.