Everything you need to know about growing cannabis at home

How to Measure pH for Cannabis Plants

by | May 16, 2022 | Cannabis, Getting Started, Troubleshooting

Cannabis plants are finicky, and if you want to grow optimal cannabis with the best taste, potency, yields, pest resistance, and more then you need to be mindful of pH. The pH of your medium can have a big impact on how well your plant takes up nutrients from the soil. When the pH is too low or high this can cause a nutrient deficiency that can lead to stunted growth which affects yield size. In this article, we will take a look at what the optimal range of pH for cannabis is as well as how to measure soil pH for optimal cannabis growth.

What is soil pH?

Soil pH is a measure of how acidic or alkaline the soil is. The optimal pH for cannabis plants in soil is between 6 and 7, but they can grow in soils with a pH as low as five and as high as eight although this is not recommended or ideal. Soil pH affects nutrient availability, so it’s important to get it right to mimic their natural environment if you want your plants to grow well. If you are growing in coco coir, which is made from the husks of coconuts, or using hydroponics, such as a water culture system where the roots are suspended in air, then optimal ph for cannabis is slightly different and we will cover those methods below.

Why is pH important for cannabis?

pH affects the availability of essential nutrients to your cannabis plant. If you get it wrong, some parts of your plant can be lacking certain nutrients and others may have too much of a nutrient that they don’t need. For optimal cannabis plant growth, make sure all the key soil mineral nutrients are available at an appropriate level (not too high, not too low).

What is the optimal pH for cannabis plants?

The optimal pH will be solely dependent upon which medium you are using as it varies for soil, coco, and hydroponics. Let’s take a look at the optimal pH levels for each below for the various mediums used by marijuana growers.
***Please note to add any nutrient solution to your water (if using liquid nutrients) or soil (if using dry amendment nutrients) before taking any pH measurement***


The optimal soil ph for growing cannabis should be between 6 and 7. Aim to keep your pH around 6.5 when measuring your runoff. The chart below shows the pH levels where different nutrients are available in the soil and why your pH needs to be between 6 and 7 for optimal nutrient uptake.

Coco Coir

The optimal coco coir ph should be between 5.5 and 6.3. When your plants of cannabis are in the vegetative stage the pH should be between 5.5 and 5.8 and in the flowering stage, the pH should be 6.0-6.3 for optimal environmental conditions.


For hydroponic crops, the optimal hydroponic ph range is between pH of 5.5 and 6.0. It is similar to coco in that the pH is lower than soil and in a narrower range. The optimal pH is around 5.8 for nutrient balance.

How do I test the pH of my medium for growing cannabis plants?

There are a few different ways to test the pH of your medium. One is to use a pH kit, which you can buy at most gardening stores. Another way is to use a soil probe. This is a metal rod that you stick into the soil and it gives you an accurate reading of the pH level. Finally, you can also test the pH of your soil and medium using a digital PH meter. If you aren’t sure which method to use, we recommend getting a digital pH pen from either Apera, Bluelabs, or Hannah Instruments. Let’s take a look at how to test the pH of the different mediums using a digital pH pen below.


There are two ways to test the pH of your soil. The first is simple enough and involves testing the pH of your runoff after watering. pH your water before watering and then pH test the runoff to see how your soil is affecting pH levels. If your runoff is too high or low, you can adjust the pH of the water you are giving them using “pH Up” or “pH down”. These are simple solutions that help adjust the pH in water where pH Down is an acidic solution while pH Up is an alkaline solution. The other way you can test the pH of your soil is by using a soil slurry. This involves scooping a little bit of the medium into a cup and adding the water you use to water your plants (whether it is tap water, reverse osmosis water, etc. just make sure it is the same water you use for feeding). Stir vigorously for a minute and then let it sit for 5 minutes. Repeat 2 more times and the last time allow the slurry to settle for 15 minutes before taking the pH with a pen. If the slurry is too high or low you can adjust the water going into the medium using pH Up or pH Down so the pH levels of the runoff are optimal.

Coco coir

You can test the pH of your coco coir similarly to how you would test the soil. You can use a soil slurry or measure the pH of the runoff and adjust your water using pH up or down as necessary and both methods are described in detail above.


To measure the pH of your hydroponic system, simply use a pH meter in your reservoir of water. If the pH of your water is too high or low you can adjust it using pH Up or pH Down.

What happens if my soil pH is too HIGH for cannabis plants and how do I fix it?

If your soil pH is too high, it means the soil is too alkaline. Besides pH’ing your water every time to the optimal level, this can be fixed by adding organic nutrients like sulfur or aluminum sulfate to lower the pH level. Be sure to test the pH before you add any chemicals and only make small adjustments at a time so you don’t accidentally make it more acidic than it already was before.

What happens if my soil pH is too LOW for cannabis and how do I fix it?

If your soil pH is too low, it means you have acidic soil and the pH needs to be raised. If you want a more permanent fix and do not want to fiddle with pH’ing your water every time, you can either add dolomite lime or wood ash to raise the level of your acidic environment in your soil; however, lime takes a long time to take effect but you don’t need as much. It’s best if you test the pH before adding anything so that you know exactly what you’re doing.


Marijuana plants need the right pH levels to absorb the correct nutrients from the soil. When your plant’s pH is optimal, it will lead to healthy cannabis plants and quality cannabis. If you’re having trouble with your pH levels, don’t worry. We’ve got all the information you need to get them back on track. Just remember to test the pH of your soil and medium regularly, and adjust the pH of your water as necessary. Thank you for reading our article, should you have any other questions please see our articles regarding mediums, soil slurries, and nutrient lock.

To learn more about growing cannabis at home consider checking out our guides on: Getting Started, Troubleshooting, and Optimizing your Grow or search our Knowledge Base.

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