How do you choose the right soil for your cannabis?
As with any plant you’re hoping to grow—smokable or not—when choosing soil there are three main elements to keep in mind: water retention and drainage, nutrients, and pH balance.
Cannabis is considered a weed (which is, you know, pretty fitting), and it’s actually a relatively hardy plant that will grow in just about any kind of soil, but the soil with the best conditions for cannabis should have:
an equal balance of water retention and drainage,
a good ratio of the nutrients nitrogen, phosphorus, and potassium (NPK), and
a lower pH, between 6.0 and 6.5.
But what makes these qualities beneficial for growing cannabis? Let’s dig in.
Water retention and drainage:
Cannabis is a plant that does best when potted, where it’s easier to control the kind of drainage and water retention the soil has. If a soil drains too quickly, the plant may not absorb the water, and will end up thirsty and more likely to wilt. If a soil is so dense that water stays trapped around the roots and hardly drains at all, the roots could develop fungus and mold, which can suffocate or kill the plant.
Obviously, we don’t want either of these things to happen to your best buds, so you want soil that’s considered “well-drained.” Well-drained soil essentially just means that there’s a good balance between water pouring from the soil as though you’ve just unplugged a leak, and water soaking into the soil as though it were a sponge.
Your soil should be a dark, rich brown, and should feel fluffy and lightweight in your hands. The best soil is about half air space and half mineral, with 2-5 percent organic matter and perlite. Essentially, when you pour water into the soil, the water shouldn’t pool on top or run right through. The kind of pot you use can also affect your soil’s drainage. If you plant in a plastic pot, you’ll need to make sure there are drainage holes in the bottom and a saucer or catch pot where the runoff can collect. Otherwise, even if the soil drains well, there’s nowhere for the excess water to go. It’ll collect at the base of your soil and you’re back at risk for fungus and molds, especially when using a grow tent. We recommend using felt pots, which allow for natural evaporation and easier absorption of nitrogen and carbon dioxide, both of which your plants need.
Nutrients (or “nutes,” as we say in the biz) are also quite important for prime cannabis soil. Odds are good that if you pick a good soil, it will already have decent nutrient levels in it, but there’s no harm in bumping up those nutrient levels a bit.
We’re not talking about old-school additives like fish heads, cow manure, or even urine (gag). While these things can help other plants grow, since cannabis has such a short grow cycle (only 90 days!), it takes too long for these kinds of fertilizers to actually break down and add nutrients to the soil.
What you should look for are organic nutrient supplements with a good nitrogen-phosphorus-potassium ratio, or NPK. Make sure you’re not using chemical nutrient supplements, though, as there are a number of reports about serious health concerns.
A good NPK ratio to start with is 2:2:2. As you get more experience growing cannabis, you can play around with these numbers. Some growers prefer a ratio of 2:1:2, and others change up their ratios as the plant grows, moving from 2:2:2 to 10:5:7 to 7:7:7 during different phases of the grow cycle, but we recommend starting at a 2:2:2 or a 2:1:2 for your first crop.
A soil’s pH levels are important because they can affect how well your plants absorb the nutrients in the soil. Generally speaking, a soil with low pH (something like a 2 or 3) is acidic. A soil with a higher pH (something like a 12 or 13) is alkalotic. A neutral pH (neither acidic nor alkalotic) is around a 7. The scale goes from 0-14, and neither end is great for growing plants.
Most plants, including cannabis, prefer a soil that’s slightly more acidic than neutral (something like a 6-6.5), because this is the sweet spot which allows your plant’s roots to best absorb the soil’s nutrients. At a 7, the roots won’t absorb nutrients very well, and at a 7.5, they wont absorb nutrients at all. Plus, a lower pH level will keep fungus and mold off your roots.
So how do you test for pH levels? Well, you could test every single bag of soil you purchase, but that’s time intensive and pricey. Or you could just pick a brand name soil with a good pH level, but pH levels fluctuate wildly, even in two bags of the same brand of soil, so that’s no guarantee, unfortunately. Actually, pH levels fluctuate throughout the lifespan of the soil and of the plant, because of the pH level of the water you use (some cities’ water is more alkalotic, others are more acidic), how the soil is stored, and how microorganisms in the soil affect the pH levels in each bag. It may seem like there’s no way to control pH levels, but that’s actually okay.
The best way to get a consistent pH level from your soil is to buy organically produced soil, as this soil’s pH should only fluctuate gradually. If you must adjust the pH levels in your soil, use naturally produced pH balancers, don’t overcompensate when applying them, and never try home remedies, as this can add unwanted chemicals to your weed.
So there you have it! You’re ready to search for the perfect soil! We’re partial to our Pot-Ing Mix, which you can buy here. Remember that it will likely take some trial and error to find the soil and nutrient combination for your grow and there’s really no substitute for hands-on experience. Happy growing out there friends.
Know something the world should about growing cannabis? Write us and let us know!