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Bad Soil pH Can Destroy a Good Grow – Protect Your Cannabis

Francis Cassidy
How Does pH Affect Plant Growth represented by hands holding soil

Here’s how pH affects plant growth in cannabis, and how to find the sweet spot.

Sometimes, its better to ask, how does pH not affect plant growth. The pH level quantifies the acidity or alkalinity of a substance or solution. Measured on a scale from zero to fourteen, a lower number represents a more acidic environment, and a higher number a more alkaline one.

Essentially the scale represents the concentration of hydrogen ions in a medium. Pure water is neutral, neither acidic nor alkaline. It contains the same number of positive charges (H+) as negative charges (OH -) and therefore lies in the middle with a pH of seven.

Substances like vinegar and lemon juice are acidic and have a lower pH. While alkaline substances like soap and ammonia have higher pH values and are said to be basic.

How Does pH Affect Plant Growth?

The pH is an essential factor in the uptake of nutrients. Different nutrients become available at different pH levels, some higher, some lower. Even if nutrients are present in the soil, certain nutrients may remain unobtainable to the plant due to incorrect pH.

How does pH affect plant growth? Well, pH varies depending on the plant’s current needs. The pH of soil and nutrient solutions is actually a delicate dance. For example, if a plant needs more phosphorous, then it lowers pH by excreting acids. If it requires more calcium, then it secrets a base from the root zone to raise it.

pH Levels Represented

ph levels represented on chart

Image via roughbros.com

Like everything that underpins mother nature, pH is in constant flux. Growers need to be aware of its potential to wreak havoc if it drifts too far. While many beginner growers try to maintain pH within a small window, it’s always more favorable to allow for and expect some variation. There’s an innate intelligence within plants, and the energy they expend in altering pH is related to nutrient uptake. By fighting against and overcompensating for these natural processes, growers fight against their plant and eventually weaken it by forcing it to expend more valuable energy than necessary to hone pH. Top growers work with mother nature and do what they can to ensure the plant directs its energy into bud sites.

What is the Optimal pH in Soil for Cannabis?

Soil is forgiving when it comes to pH values, and the optimal pH is between six and seven (logarithmic scale). However, there is no set number within this range that is “best.” Instead, it can be good to allow for some natural fluctuation within this window to support optimal nutrient uptake.

If growing purely organically—where growers do not administer liquid nutrients—pH is less of an issue. By using amended and composted soil with organic matter, the microorganisms within will make the nutrients more available to the roots. However, most growers using standard potting mixes and liquid nutrients will indeed have to reckon with pH.

How Does pH Affect Plant Growth represented by woman testing soil with meter

What is the Optimal pH for Soilless and Hydroponic Setups?

Acceptable pH drift for soilless and hydroponic setups is between 5.8 and 6.4. Control of pH is much more critical in such grow setups. Due to the fact that nutrients are administered to the root zone through watering, pH can fluctuate wildly, and there’s always an increased risk of pH falling outside of the recommended range for a considerable time. Most growers will set the pH of nutrient solutions to six. From there, the plant will secrete acids and bases from the root zone to adjust pH for optimal nutrient uptake.

How Does pH Affect Plant Growth? How to Test pH

Several solutions exist for measuring pH, but the most common methods are via electronic meters or through testing strips. Electronic meters provide a simple hassle-free way to obtain an accurate measurement, although they must be calibrated with a substance of a known pH like distilled water before use.

Testing strips contain a series of indicators that change color once exposed to a solution. With a liquid in a container, simply dip the strip into the sample, and a few seconds later, take the reading by comparing the color to the color chart that accompanies the kit.

When it comes to measuring the pH of soil, mix the soil with distilled water, and pour it through a coffee filter before using a preferred method. Repeating this process with several soil samples and calculating an average will provide more accurate readings.

What To Do if pH is Too High or Low

If pH falls outside of the recommended range for a considerable time, then the grower must intervene to save the plant. Any potential disaster is easily averted by using the ‘pH up’ or ‘pH down’ products available at any grow store.

A little goes a long way. Always use small amounts of these products and measure after each application until the pH is back in range. One thing that greatly affects pH is tap water. Given its alkaline nature, many growers will find they need to lower pH more than raise it.

Managing pH may seem daunting to many growers. But when regularly monitored in a healthy medium and allowed to vary naturally within its window, there’s generally little that can go wrong.

Francis Cassidy

Francis Cassidy is a freelance writer who writes on a variety of topics. With a particular focus on the cannabis industry, he aims to help ensure the smooth reintegration of cannabis back into global culture. When not writing, he's to be found exploring his new base in British Columbia, Canada. You can follow his other works including his photography on his blog thestrayphotographer.com

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