Decode Your Cannabis Grow by Testing Your Soil

holding a bunch of soil

If you ask a cannabis farmer for their growing tips, they'll usually start talking about soil.

Most farmers are passionate about their soil. Some organic growers are downright evangelical about it. If you want to grow your crops without chemical pesticides or fertilizers, you need healthy soil. A good step toward maintaining healthy soil is soil testing,

What is Healthy Soil?

holding plant outside

Healthy soil is made up of a complex ecosystem of living organisms. In a single handful of healthy soil, billions of microorganisms are feasting, digesting, breathing, and dying. Soil is alive.

To grow healthy plants outdoors, you need those soil organisms. Below the surface, they're engaged in a complex give-and-take with the plant roots. They're breaking down detritus in the soil, and converting it into nutrients that plants can use. They're also fighting off pests and pathogens that might otherwise plague your plants. If your soil doesn't have these beneficial bugs and bacteria, your plants will be more susceptible to pests and parasites.

Maintaining healthy soil can be hard work. But it's worth it, according to most biodynamic organic marijuana growers. These growers tend to be skeptical of hydroponic growers. (The soil-versus-hydro debate can be controversial.) Organic growers often claim that hydroponic cannabis can never mimic the flavor and aroma of cannabis grown in soil.

The flavor of a cannabis crop can be impacted by the soil it's grown in. This is true for many crops, but especially those with nuanced flavor profiles, like cannabis and wine. (This is why wine connoisseurs often talk about the "terroir" of their favorite vineyards.)

Which Growers Need Soil Testing?

soil and plants budding

If you're growing cannabis or hemp outdoors, a healthy soil ecosystem is essential – especially if you're using organic or biodynamic practices. If you're growing indoors, you may still need a healthy soil ecosystem in your pots.

Of course, if you're growing indoors, you might be using hydroponic or aquaponic methods. (If you're growing your plants in coco, or some other medium, you obviously don't need soil testing, because you don't have soil.)

And if you're growing outdoors in pots, you still may not be interested in soil testing, either. Depending on the size of your growing operation, you might just purchase all your soil from a grow supply store. In that case, you can get all the information about your soil from the manufacturer.

However, if you're planting directly in the ground, you may want some basic information about your soil. This could save you money and time, because you'll have a better idea of what your soil needs. That way, you won't over-apply the wrong nutrients. You'll have a better idea of what nutrients are deficient – and where to spend your money most efficiently.

However, if growing a few cannabis plants is just a hobby for you, you may not want to invest your money into soil testing. You can just start growing your plants, and see how they do. Then you can adjust your soil accordingly – the way home gardeners have been tinkering in their gardens for centuries.

Of course, if you're growing cannabis or hemp on a commercial scale – if you've invested in your crop, and you intend to profit off it – you'll definitely want to test your soil. If your crop ever exhibits signs of infestation, or nutrient deficiencies, you'll find yourself urgently in need of soil testing – so you can address the problem, with science on your side.

What Can a Soil Test Tell You About Your Soil?

touching soil

A soil test can tell you about your soil's acidity (or pH), its nutrient levels, and its composition. These are all important factors to consider when growing any crop, including marijuana or hemp.

Soil testing can tell you about the pH of your soil, or how acidic it is. The pH scale runs from zero to 14. If your soil has a pH of seven, that is considered a "neutral" pH. (The acronym stands for "potential hydrogen.") If the pH is below seven, it's acidic. Soils with a pH above seven are considered alkaline.

Some experts believe cannabis plants thrive in a slightly acidic growing medium. If your soil is slightly acidic (somewhere between 6.0 and 7.0, on the pH scale), the roots should be able to absorb nutrients easily. Others say your soil should closer to neutral (closer to 7.0).

If your soil is too alkaline (if it scores above 7.0 on the pH scale), the nutrients in it won't be available to your plant roots. To fix this problem, you can add organic matter, to help reduce the pH. Most gardeners use compost. You could also use animal manure. Especially if you live on a farm, or in a farming community. (If you don't know any farmers, check Craigslist. Many livestock and dairy farmers will sell you animal manure for cheap. But if they don't deliver, and you don't own a dirty pickup truck, you're in a bit of a pickle: Nobody wants to move a bunch of cow manure in a Tesla.)

Organic matter is the lifeblood of the soil. Basically, it's the part of soil that used to be alive. (On a farm, it's mostly manure; in a forest, it's mostly the dead leaves that fall to the ground.) Decomposing matter gets eaten by microbes and bacteria, which convert it into nutrients that can be used by plants.

Organic gardeners have been adding compost to their soil since the dawn of farming. If you're growing cannabis, or hemp – or pretty much anything else – amending your soil with high-quality compost is definitely not going to hurt.

Soil Testing Can Make You a More Informed Grower 

live macro shot of cannabis plant

You can buy a basic soil testing kit at your local gardening store. It won't run you much more than twenty bucks.

Then you'll have detailed information on your soil. You can figure out how much compost to buy, and whether you want to decrease or increase your soil pH.

Like any dedicated organic gardener, you may want to take notes. Talk to your neighbors. Start a gardening journal. Start a spreadsheet. Go nuts.

If you're not into DIY science projects, you can also mail a soil sample to your local agriculture extension service. Depending on what kind of test you purchase, you may be able to get personalized recommendations. This is the more expensive option, but – provided you collect an accurate soil sample to mail in – you'll get a more detailed scientific report.

As a home grower, if you're even thinking about soil testing, you're ahead of the game. You clearly understand the importance of healthy soil. You know that, as a grower, the most important thing may not be your green thumb. It may be what's happening below the surface.


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Cecelia May Thorn
Cecelia has been working in the cannabis industry since 2009. She's also an award-winning journalist. In 2012, her small business became Colorado's first state-approved wholesale marijuana brokerage. She's pretty sure that made her the first official weed broker in America. Follow Cecelia on Instagram: @ceceliamayusetoomanywords