How to tell if your soil is healthy enough to grow cannabis

Published Jul 27, 2022 09:00 a.m. ET
iStock / Khanchit Khirisutchalual

The outdoor growing season is here and what you get at the end of it all come harvest is closely linked to the health and overall condition of the soil. But how do you tell if your soil is good enough for growing cannabis, and if it’s not, is it possible to make improvements?

Knowing your soil

Take a large plastic sheet and use a shovel to dig down approximately 2 inches where you plan on growing cannabis. Peel back the grass, and topsoil before reaching just a bit deeper towards what should be a darker base. Make two piles of soil, one being the lighter contents and the other from 4-6 inches down, and then take a good look at it all.


Is it dark or light-coloured? Dry and sandy or tacky and sticky? Does it smell like fresh earth, or are there other scents thrown in you don’t quite recognize? These are all very important characteristics to note. Though it might be difficult to thoroughly assess soil health through visual inspection alone, it’s an excellent first step towards getting to know your soil.

Gathering samples for testing

For this part, you’re going to need two plastic baggies with durable seals. Use the shovel to stir both piles individually and put a scoop from one of them into a bag. Seal the baggies and label which layer it is from using a permanent marker. Now take a scoop from the second pile and repeat the process.

Getting answers

Next, you’ll want to pick up a simple soil testing kit which can be found at pretty much any greenhouse, feed, or department store, for an affordable average price range of $10.00-$30.00. This will give you all the information you need about things like nitrogen, phosphorus, acidity, and potassium. Sadly, they won’t deliver data where micronutrients are concerned, but if you’d like to dissect the situation that deeply, then there is always the option of having it tested through a provincial lab.

The last way to gauge the health of the soil is to sit back and watch what happens throughout the growing season. If you’re able to grow cannabis that’s healthy, bountiful, and satisfactory, then you’ll know that the soil is probably ok. However, if your crop is struggling to thrive, it might be time to take the next step and get some testing done.

Types of soil

Sandy soil isn’t usually ideal for growing cannabis plants, because it doesn’t retain water or nutrients for as long as dense soils. The root system may penetrate sand with ease, but the overall health of the crop is likely to suffer without a little help. Loamy soil on the other hand is typically much better for growing cannabis or vegetables, but it is generally mixed due to high acidity. Clay soil is a type of cold soil, that takes far longer than sand and loamy soils to warm up, but it is superior at retaining nutrients and moisture, as long as it’s combined with another type. Otherwise, clay is challenging for root systems to navigate.

If the soil in your garden isn’t ideal yet, fear not because there are things you can do to improve the health of a garden plot.

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Additions to improve soil health

Peat moss is highly acidic, but it boasts an incredible ability to hold nutrients and water, which makes it perfect for alkaline or sandy soil.

Topsoil isn’t generally very high quality, but if you’re looking to reduce acidity or raise your garden, it could be the ideal addition to your garden.

Compost is a beautiful addition to any garden, but its quality heavily depends on what you put into it. If it is indeed a mixture of nutrient-dense scraps, then adding some to your garden can help to improve its structure.

Manure adds a high dose of nitrogen to the soil, and it works best in combination with compost.

Sun, drainage, and digging

Now that you have a better idea of soil structure and nutrients it’s time to go over other important factors like sun, drainage, and digging. Growing cannabis plants need a minimum amount of light exposure each day, with most cultivators opting for 6+ hours.

Sandy soil doesn’t have an issue with drainage, unless your water table is higher than usual, and in those rare situations raised garden beds might be the best solution. Digging walkways deeper can help to displace water when it gets too high in your garden, as can small drainage channels, directed away from the plot.

No dig gardens are most compatible with soil that isn’t too heavy, or wet, or those with lower concentrations of clay. With these gardens, care is as easy as adding a few layers of compost each year, combined with manure.

What to do if your yield goes down

If at any point you notice that your cannabis plants aren’t faring as well as you think they should, then it’s a good idea to gather more samples and conduct further testing. Perfecting soil health is a science that isn’t always predictable for those who aren’t innately aware of the needs of a crop, so it’s not uncommon to get things wrong, especially if it’s your first time. With testing, you’ll save both time and money that might otherwise be spent adding unnecessary and in some cases even damaging additional ingredients to the plot.

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