by Nebula Haze
When it comes to growing cannabis in soil, unless you're using a brand that is known for making soil that is specifically cannabis-friendly, there are a few things that you need to consider before starting a grow.
Important Cannabis Soil Considerations
- Drainage Ability
- Water Retention
Although that list looks vague and complicated at the same time, the requirements you want to meet are actually pretty simple; let me break it down!
Texture, Drainage & Water Retention
It's easy to get caught up thinking about what nutrients and amendments are in the soil, and those are important, but perhaps the most important aspect of any soil is actually its texture, ability to drain, and overall water "holding" ability.
In order for a cannabis plant to grow and thrive, it needs a good mix of both water and oxygen at the roots at all times! Too much water and the plant roots can't get enough oxygen (lack of oxygen at the roots is why plants get droopy from overwatering) but on the flip side if there's not enough water retention the roots can be injured from drying out too quickly!
What gets the best results for growing cannabis is a soil with a light texture that is good at retaining water…but not too much!
Note: Don't worry, there'll be examples of good and bad soil in just a bit!
Signs of Good Cannabis Soil
- Appears dark and rich
- Loose texture
- Drains well (doesn't make a pool on top of your soil for more than a couple of seconds and doesn't take forever to drain out the bottom)
- Holds water without getting muddy (you want wet soil, not dirt-batter)
Example of "Good" Cannabis Soil Ingredients
- Composted forest humus
- Sandy loam
- Sphagnum peat moss
- Coco coir (sometimes labeled coco fiber)
- Earthworm castings
- Bat guano
- Fish meal
- Crab meal
- Bone meal
- Blood meal
- Dolomite lime
Note: You'll likely never see any soil mix with ALL those ingredients, but I wanted to share examples of common cannabis-friendly ingredients and amendments that often appear on the label of good soil 🙂
If you get the soil part right, you have almost everything you need to get to harvest! With the correct texture, drainage and water retention, you've got a perfect base. Add good soil cannabis nutrients, especially in the budding phase, and you should get to harvest with great results!
Example of happy marijuana plants in good soil!
More About Common Amendments to Alter Texture, Drainage & Water Retention of Soil
Perlite is one of the most common soil amendments. It is highly recommended for any soil mix that doesn't have some already.
Very light, airy white "rocks" that feel almost like popcorn and add oxygen while increasing overall drainage ability.
Add perlite to the mix (10-40% of the total volume). Use less perlite if you want better water retention and don't plan on using a lot of extra nutrients. This is because a lot of extra perlite can cause the nutrients leach out faster from the soil. Add higher levels of perlite if you want to use a lot of added nutrients or supplements without burning your plants (since perlite helps prevent nutrient buildup).
Vermiculite "lightens up" heavy soil and improves water retention.
Some growers use perlite and vermiculite interchangeably, though they're not exactly the same. Vermiculite holds water much better than perlite, but is not as effective at adding aeration and drainage.
Some growers use a little bit of both. If you go high with vermiculite, you don't want to go as high with perlite and vice versa. Together, perlite and vermiculite should never make up more than 50% of your soil!
Coco coir is made from coconut husks. It can be purchased as loose coco coir, in an amended potting mix, or as coco bricks which needs to be rehydrated before use (learn how to re-hydrate coco bricks). Sometimes you'll find a "soil" mix that is pretty much all coco plus amendments, and these can be a great choice for cannabis. Coco has some unique properties that make it a good supplement for cannabis soil mixtures.
Coco improves water retention, but doesn't make soil heavy.
Roots tend to develop faster and plants are less likely to suffer from overwatering in coco coir.
Some growers grow in pure coco, but if you're adding it to a soil mix as an amendment, you might add 10-30% coco coir.
Worm castings is a nice way of saying worm poop, and cannabis plants love it!
Improves texture, drainage and moisture retention
Add a natural source of nutrients that breaks down slowly
Usually contains high levels of beneficial micro-organisms due to going through a worm's digestive system 🙂
Add up to 30% worm castings in your soil (although it contains nutrients, it's gentle enough that it's unlikely to burn your plants even if you add too much)
Now here are a few examples of good and bad cannabis soil so you can see the texture you're looking for!
Good Cannabis Soil
Rich and light composted soil. Since this soil doesn't have a lot of perlite, it's a good choice for a grower who doesn't want to add a lot of extra nutrients or supplements in the water.
Good Cannabis Soil
Another light, rich soil mix with great drainage. Although there is a wood chip in this picture, for the most part the mix is completely composted and broken down. It's normal to see some wood pieces in composted soil, but you don't want to have to wait for a lot of wood to break down while your plants are growing – you want all that rich nutrient goodness to be readily available to your plant roots 🙂
Good Cannabis Soil
This soil has quite a bit of perlite, which is a good choice if you plan to feed heavily with nutrients and supplements since the extra perlite prevents nutrient buildup in the soil
Good Cannabis Soil
The plant is growing in organic, composted "super soil" which has enough amendments to last your entire grow, so the only thing you do is add water!
Here's organic "super" soil up close
Bad Cannabis Soil
This soil is muddy, clumpy and waterlogged. It retains too much moisture, which makes it really easy to overwater your plants.
Bad Cannabis Soil
Cannabis soil should not have a whole lot of big visible wood chips in it. That means the soil hasn't been fully composted, and all the nutrients and goodness in that wood is mostly unavailable to your plants.
Bad Cannabis Soil
Although this seedling is over a month old, it has stayed tiny. Its growth is stunted by the thick heavy soil that holds way too much water and not enough air. Note how some of the soil looks like one solid object.
Bad Cannabis Soil
Don't use dirt from outside! It almost never works, especially if it looks like this!
Fox Farm Ocean Forest Soil
Fox Farm has been around for over 30 years and makes some of the most common types of "cannabis soil" (at least in the US). They have several great soil mixes, including "Happy Frog" which is a great choice for seedlings and clones.
Their Ocean Forest soil mix is "hotter" soil (higher levels of nutrients) that contains ingredients that cannabis plants love, including earthworm castings, bat guano, fish meal and crab meal. The nutrients contained in the soil will provide everything your plant needs for several weeks. Although it might give young seedlings just a touch of nutrient burn at first, they can be started in Ocean Forest soil and will soon be able to use the nutrients and start growing quickly. Some growers might put a little big of Happy Frog on top of a container of Ocean Forest, just to make it a little more gentle for seedlings the first week or two.
If you are willing to keep transplanting to bigger pots as your plant uses up the nutrients in the soil, you don't need to supplement with extra nutrients. However, even if you grow in the same pot from seed to harvest, Fox Farm offers a complete nutrient system that is also formulated for plants like cannabis and goes perfectly with their soil to make sure your plant is getting the right levels of nutrients throughout its life.
This plant is growing in Fox Farm Ocean Forest Soil
Kind "Super" Soil (Living Soil)
When cannabis growers talk about "super" soil, they're usually referring to soil that has been amended with slow-releasing organic nutrient sources, and then composted for several months (learn more about super soil).
The composting process creates a "living" soil that is full of microorganisms in the rhizosphere (area around the roots). Properly composted soil has nutrient sources that slowly break down over the course of your plant's lifecycle. It very closely mimics what happens in nature.
Super Soil has a colony of micro-organisms living in the soil which form a symbiotic relationship with your plant roots. They deliver nutrients to your plant, and in return they eat the sugars that get secreted by your roots!
The "micro-herd" in the soil delivers nutrients directly to your plants. As long as you're using decent water, you usually don't need to worry about pH or other things that can disrupt nutrient absorption in regular soil.
Buy Pre-Made Super Soil Compost (just add water!)
However, when growing with Super Soil, it's a good idea to avoid watering too much at a time, as extra runoff waterwill drain away some of the nutrinets. Try to give just enough water to saturate the soil with very little extra coming out the bottom. Since you won't be adding more nutrients through the grow, you want to conserve what's in the soil!
Nugbuckets is a famous organic soil grower! Check out his plants!
Organic Potting Mix
This is what kind of soil to get if you don't have any "good" soil available, but want something that is known to work for growing cannabis.
Generally, anything labeled as an "organic potting mix" will work. This type of mix hasn't been amended with chemical slow-release nutrients, which is one of the main things you want to avoid with soil for cannabis. I know it sounds like heresy, but even the Miracle-Gro version of "organic potting mix" will work okay, because unlike their original potting mix it doesn't contain chemical nutrients (though it still has poor drainage and moisture retention – almost any other type of organic potting mix is better!).
Usually an organic potting mix does not have enough nutrients to last your plants for more than a few weeks, so it's a good idea to always supplement with cannabis-friendly nutrients, especially in the flowering stage when your plant is making buds and needs lots of extra Phosphorus and Potassium.
Espona Organic Potting Mix is found in many stores in the US, and works for growing cannabis!
What to Watch Out For With Any Soil Mix At the Store
Look At and Touch It If You Can! You already have an idea what soil should look and feel like, but here's a test: If you form the soil into a ball, it should stick together loosely, but it should also easily fall apart again if you squeeze it.
No "Time Release" Chemical Nutrients in the Soil – These types of soil slowly release nutrients over the course of months, which provides too much Nitrogen in the flowering stage and could possibly impair overall bud growth.
Soil Should Appear Dark and Rich – Pale, crumbly or sandy soil usually doesn't have a lot of nutrient content that the plant roots can get to.
Soil Has Little White Rocks In It (Perlite), if you see white, almost fluffy rocks dispersed through the soil like popcorn, that is usually a good sign because it means this potting mix was intended to have good drainage.
Soil Isn't "Heavy" – Cannabis grows best in soil with a light airy texture and great drainage, which may seem almost fluffy when it's dry.
Example of "Good" Soil Ingredients – Composted forest humus, sandy loam, sphagnum peat moss, coco coir (sometimes labeled coco fiber), perlite, earthworm castings, bat guano, fish meal, crab meal, bone meal, blood meal, Azomite, pumice, kelp, dolomite lime, mycorrhizae and leonardite. That's not everything, just examples of cannabis-friendly ingredients you see the most often 🙂
Examples of "Bad" Soil Ingredients – You don't want to see wood or bark on the label if it doesn't say it's been composted first. Also if you see just the word "fertilizer" in the ingredients that's often code for slow-release chemical nutrients, which you don't want!
Try to get soil that looks like this!
I hope this soil tutorial helps you find the right soil for your cannabis setup!
No! Bad Soil!