In Understanding Soil pH: A Beginner’s Guide, we talked briefly about what pH is and how it relates to cannabis. This time, we’re digging deeper! In this article, we’ll look at the importance of pH for cannabis growers and introduce environmental factors into the equation.
Maintaining the optimal pH for your plants may seem complicated, but it doesn’t have to be. BlueSky Organics has quick and easy solutions to help you balance your soil and let your plants thrive. Let’s dive into why pH is important.
What is pH?
As covered in our beginner’s guide, pH is a measurement of how acidic or basic a solution is. pH stands for potential of hydrogen. Confusingly, a greater potential of hydrogen (more hydrogen ions available) corresponds with a lower pH. Before we dive into the concept of soil pH, let’s look at what makes a solution acidic or basic.
An acidic solution has many hydrogen (H+) ions and a basic solution has many hydroxide (OH–) ions. A solution that is balanced in these ions is considered neutral.
One hydrogen ion combined with one hydroxide ion produces H2O, which you may recognize as the chemical formula for water. Pure water lands in the midpoint of the pH scale and is considered a neutral solution.
A pH scale is logarithmic. It has 14 points, each representing a tenfold increase in basicity. A solution with a pH of 4 has 100 times more hydrogen ions than a pH of 6.
Understanding Soil pH
Cells in the human body have a relatively neutral pH of around 7.4, as do most living things.
Just as we don’t worry about maintaining the pH inside our own bodies, the internal cellular pH of our plants is not a concern. The pH of the soil environment, however, is a top priority.
To better understand soil pH, it can be helpful to think of soil as a liquid. Many of the nutrients in soil are water-soluble and dissolve into the soil. This helps to keep the nutrients mobile and gives the soil an overall pH.
The soil pH is determined by the chemical compounds in the soil, whether they are acidic or basic. Common acid-forming molecules in soil are hydrogen, aluminum, and iron. Common base-forming molecules are calcium, magnesium, potassium, and sodium. Sound familiar? These are some of the key macronutrients and micronutrients required for plants to grow. We’ll come back to this later.
Factors Affecting Soil pH
Acidic and basic soil can come from four different sources:
Basic soils with a pH higher than 6.5 are known as alkaline soils. Alkaline soils absorb water very poorly, making them very difficult to grow with. Rice is an exception and can be successfully grown in alkaline conditions.
In our recent composting article, we followed how organic materials are broken down by microorganisms into valuable nutrients. These nutrients, as mentioned above, are also acid and base-forming molecules. When organic material is broken down, these molecules are released and change the soil pH.
Non-organic fertilizers often come with instructions to apply a balancing agent. This helps to counteract the pH altering fertilizer. For example, acidifying ammonium fertilizers require the application of lime, which is basic, to ensure that soil pH doesn’t shift drastically.
A simple way to avoid this balancing act is to grow organically. Organic fertilizers contain nutrients that are slowly broken down to help maintain a balanced soil environment.
Leaching is the loss of nutrients and minerals from the soil surrounding plant roots. Excessive application of water can cause leaching and shift the soil pH into non-optimal ranges.
Soil pH is constantly changing due to environmental factors. To make sure that pH fluctuations are within a healthy range, we must regularly monitor a soil’s pH. Thankfully, monitoring soil pH is quite straightforward.
pH for Cannabis Growers
Cannabis plants can only thrive with the right nutrients, in the right amount and at the right time. In our articles on macronutrients and micronutrients, we discuss what the right nutrients and right amounts are. These factors are crucial in preventing nutrient lockout.
Nutrient lockout refers to soil conditions preventing certain nutrients from being taken up by the plant. One example is having excessive nitrogen in the soil, which prevents calcium from being absorbed. This can lead to symptoms of a calcium-deficiency, even when there is plenty of calcium present in the soil.
Apart from one nutrient overwhelming the plant’s ability to take up another, pH can affect the capacity for soil to hold onto nutrients. The size and charge of a nutrient molecule affect whether that nutrient can be easily displaced from the soil and washed away.
In chemistry, negative and positive charges attract each other and similar charges repel. At a high pH (where the soil has many negative hydroxide ions), positively charged nutrients can easily stick to the soil. This strong binding makes it more difficult for plants to draw up nutrients, resulting in poor soil for growing.
Conversely, at too low a pH, nutrients won’t stick and can easily be washed away. This can lead to imbalances and levels of nutrients that are toxic or deficient. For this reason, most plants prefer a moderate, relatively neutral pH.
Depending on the plant’s nutritional demands, slightly acidic or slightly basic conditions may be preferred. Nutritional demands also change based on the stage of growth that a plant is in. For a grower, knowing the preferred conditions for your crops during these stages is essential for optimal plant growth.
Organic Growing & pH
Beneficial microbes and fungi are key factors in sustainable success. Organic fertilizers are non-burning, adding nutrients to the soil that can be slowly broken down by microbes. This ensures that the plants aren’t shocked or “burned” by rapid changes in their environment.
Perhaps unsurprisingly, beneficial microorganisms also have preferred pH ranges. Researchers from North Carolina State University recommend a pH of 5.8 to 6.2. This range satisfies the microbes in soil, while providing a balanced nutrient profile for optimal growth.
What BlueSky Organics Can Offer
Organic growing produces hardier, drought and disease-resistant plants. It also produces cannabis of higher quality and yield, in a process that is environmentally-friendly. What more could a grower ask for? Follow your Custom Grow Calendar for proven cannabis growing success.
- Whipker, B. et al. (2019). New Research Results: Optimal pH for Cannabis. Cannabis Business Times. Nutrient Matters. North Carolina State University.
- Horneck, D. et al. (September 2007). Acidifying Soil for Crop Production. Oregon State University, University of Idaho, Washington State University.
- Mickelbart, M. and Stanton, K.M. Soil pH – Commercial Greenhouse and Nursery Production. Purdue University.
- Vossen, P. Changing pH in Soil. The University of California.
- McCauley, A., Jones, C., Olson-Rutz K. (2017) Soil pH and Organic Matter. Montana State University
- Fondriest Contributors. (November 2019). pH of Water. Fundamentals of Environmental Measurements. Fondriest Environmental Inc.