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How To Manage pH Levels

Super Soil: How To Manage pH Levels

Other than a crop of some great marijuana, the nice thing about growing cannabis is that you can become completely absorbed in the process. Every little thing you learn about the plant can translate into a better final product. In case our Super Soil series wasn’t sciency enough, it’s time for a little chemistry. This segment will tell you everything you need to know about managing pH levels. 

  In chemistry, pH is a numerical scale used to test the acidity or alkalinity of a given substance. The scale ranges from numbers 1 through 14. The lower the number, the more acidic. The higher the number, the more alkaline. A pH of 7 is neutral.

Hydrogen is what is actually being measured by the pH scale. In fact, pH stands for “power of hydrogen”. Acidic substances contain more hydrogen while alkaline substances contain more hydroxide.

Why care about pH?

  Talk to most marijuana growers, and they’ll recommend testing the pH of your soil. Many also go as far as testing the individual substances they add to the soil: the water, plant food, compost, etc. Some may find this a bit excessive, but pH is actually quite important.

The right pH ensures that your plant roots can absorb the nutrients in the soil. If you plant your cannabis in soil outside of its preferred pH range, you’re not going to see a great yield and your plant may actually struggle to survive. Different plants have different preferred pH levels, but marijuana likes things to be a little on the acidic side.

The optimal pH for cannabis about 6.0. However, the plant does alright with a pH as low as 5.8 and as high as 6.5. It can tolerate an even wider range, but you’re not going to get the desired productivity.

Keep in mind that every time you go down or up a number on the pH scale, the nature of your soil changes significantly. A pH of 6 is ten times more acidic than a pH of 7. Plant-beneficial soil microbiology is drastically hindered when pH levels are too high or too low. Useful fungi, for example, prefer a slightly acidic pH between 2 and 7. Bacteria prefer more alkaline environments between 5 and 9.

If you’ve planted in a high-quality soil and your plant is showing signs of nutrient deficiency, pH might be to blame. Since pH is what enables your plant to take in nutrients through its roots, simply adding in more nutrients won’t do the trick if your issue is with pH. So, testing pH is very important for diagnosing issues with your plants.

So how can you test your pH?

There are several ways of testing the pH of your soil. Fortunately, you can fairly accurately determine soil pH yourself right at home. Here’s a brief run-down of pH testing equipment.

Color kits

One of the most common ways to test pH at home is a universal indicator kit. You can purchase these kits at any local hardware or gardening store, and they’re also available online. A color kit uses a solution that creates distinct color markings for each pH level. The La Motte Soil pH Testing Kit is a great choice for looking at soil specifically. You simply collect soil samples into a test tube, add the solution, and match up the resulting color.

General Hydroponics also makes a drop solution that you can use to test samples of your water. To determine pH with a dropper method, it’s best to test both the water going into your plant and the water coming out of the bottom of the container. Another common option is a paper test. With a paper test, drop a bit of water onto a special kind of paper. The paper then changes color based on the pH of your water.

pH probe

A soil probe is another easy way to get a decent understanding of your pH. They’re a little spendier than color tests, but a decent electric probe will give you a high level of accuracy. The one big downside is that you also have to have the correct solutions to avoid contaminating the probe with materials other than those you desire to test.

The Oakton Ecotestr Waterproof pH Tester has a good reputation among gardeners.

Professional testing

If you have a little time to wait, professional soil testing surprisingly fairly inexpensive. For around $15, the Soil and Plant Tissue Testing Laboratory at the University of Massachusetts will give you a basic analysis of your soil. Getting your soil professionally tested will not only test the pH of your soil, but they will give you an accurate readout of your nutrient levels, lead levels, cation exchange capacity, among several other features.

Many states have other more local options as well, but public soil testing laboratories are a little scarce these days.

Here’s how to resolve pH issues

In nature, soil pH is largely determined by weather patterns, native rocks, and surrounding plant species over time. As most cannabis is grown indoors in pots or outdoors in secluded areas, growers don’t typically have the luxury of recreating the plant’s natural habitat. When pH needs to be adjusted, most people err towards a couple of different additives.

pH Up/ pH Down

General Hydroponics’ pH Up and pH Down products are some of the most commonly used pH regulation products in the industry. You can use them to adjust the pH of your water before adding it to your plant. Apply water with the appropriate pH is a must to maintain the pH integrity of your soil. 

Additional options

  Common pH fixing products are considered safe to use on your plants. However, if you’re concerned about maintaining the integrity of your soil microbiology, there are some additional ways to manage pH. One of the easiest things to do is to simply add organic matter (like compost) that already had the correct pH.

If you want to majorly adjust your outdoor soil without additives, it’s best to plan ahead. If your soil is too alkaline, applying mulches containing tree bark and pine needles will cause it to become more acidic over time. If your soil is too acidic, adding a little wood ash or lime will help bring up the pH. Just be cautious with the lime, as too much will quickly cause your soil to become too outline.

Consistently applying aerated water and compost teas with a neutral pH will also help maintain the right balance over time. You can also make your compost tea slightly acidic by including fungal foods like humic acid. Feeding fungus helps acidify your soil.

Additives that distort pH


Adding excess salt to your soil causes the pH to be more alkaline. If you want to avoid upping the pH level of your soil, stay away from products that contain sodium. Salts also dehydrates organisms that live in the soil, which decreases soil health. This, in turn, takes vital nutrients away from your plants.


If you’re planting in containers or in a raised bed, your plants most likely won’t be around much limestone. However, if you’re one of the lucky few that can grow outdoors in the ground, limestone can up the pH of your soil. Regions with high amounts of limestone tend to have more alkaline soils.

If you live in one of these regions, you may be better off planting in a raised bed or altering your soil by lowering the pH. You’ll also probably have to test the pH frequently and/or watch your plants carefully for signs of distress.

Conifer forest growing

Another environment to be wary of is the conifer forest. Conifers like fairly acidic soil and lots of fungus. While marijuana thrives in soil that’s slightly acidic, the herb doesn’t require as low of a pH as a fir tree does. It also prefers more bacteria in the soil than what you’d find out in the woods. So, investing in some high-quality potting soil with the right pH is a must.

Synthetic fertilizers

  Many common synthetic fertilizers can make your pH more acidic. To help maintain the integrity of your soil, avoid fertilizers that contain sulfur and ammonium. Synthetic fertilizers and other chemical additives also have a drastic impact on soil microbiology. When you decrease the soil microbiology, you decrease the amount of nutrients and trace elements available to your plant. This can significantly impact plant health.

When you get down to it, growing marijuana can be a complicated process. There are so many variables to consider! Maintaining appropriate pH is one skill that even casual growers will want to have. The right pH levels will enable your plant to consume the key nutrients it needs, thrive, and produce a quality crop. And hey, tasty marijuana is definitely a good reason to get a little nerdy about your soil.

 Do you have any pH levels management tips? We’d love to hear them!
Share them with us on the comments below.