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The Best Soil For Marijuana | Growing Tips 2020

One of the most frequently asked questions about home growing concerns selecting the best soil for marijuana, sometimes also known as the medium. There is no single correct answer. Many factors must be considered, including location, budget, previous experience, cultivation technique, and strain selection.

In this article, we will examine these variables and help you choose the best soils for marijuana growing.

Jerry Golick

Published June 3, 2020

Updated July 2, 2020

Type of Soil to Avoid

Before we can talk about some of the best soil for weed, there are a couple of options which should not be considered:

Non-Organic Soil with Fertilizers: Most major garden supply companies offer pre-mixed soil for flowers, vegetables, etc. These should be avoided since they are generally too “hot,” which is another way of saying they have too much fertilizer causing young cannabis plants to burn.

Soil from your backyard: Besides containing an unknown quantity of nutrients (and possibly pests), topsoil tends to be very dense, not allowing marijuana roots to grow properly.

Wild cultivation: While it may be possible in some cases to merely put cannabis seeds into the ground and have them grow; this is rarely effective. If you want the best soil for weed, it needs to be prepared.

Close-up of Cannabis plant growing outdoors in soil

Soil Options for Growing Weed

Don’t worry, even though we can’t use any of the above mediums, there are still plenty of options available for all budgets and situations.

Unfertilized potting soil

Potting soil is a good option, not too dense, no nutrients, and very forgiving if you make any errors. This is a great choice for beginners since it is also the least expensive option. Potting soil should only be considered when using containers (pots, bags, etc.).

Organic soil

If you intend to grow outside in garden beds, then this might be a good option. Many growers swear by the use of organic soil, claiming it makes the cannabis smoke sweeter to the taste, and healthier. While there is still no objective evidence, many people do seem to prefer organic soil. There are a wide variety of “recipes” on the internet about how to make your own organic soil. Usually, this involves starting with a neutral medium (such as a high-grade topsoil) and then adding different supplements (worm castings, lime, compost, etc.) to get the right ratio. Finding the correct ratio can take time, and so I do not recommend this for beginners. While you can use organic soil indoors, you must be very careful not to introduce pests, mold, etc.

Coco coir

Made from the husks of coconut shells, coco coir has become a very popular option for both indoor and outdoor growers. Coco coir does not require perlite or vermiculite to make it less dense because one of its key features is drainage. It is almost impossible to overwater a plant in coco coir. This makes it an excellent choice for indoor growers. However, it is expensive compared to other options.

Expanded Clay Pellets, Perlite, and Rock wool

When growing weed using hydroponics (in water), it is possible to use a variety of other mediums. Besides coco coir, you can choose expanded clay pellets, perlite, and rock wool. I won’t be discussing these in this article, since my focus is on growing in soil, which means not hydroponically.

Soil Considerations

Regardless of the medium you select, there are several variables you should consider when purchasing your marijuana growing soil:

Drainage: Purchase soil that has good drainage because plants will not do well if the roots get soggy. Most potting soils can do this reasonably well, as does coco coir. Of course, even the best soil for marijuana will get soggy if you water too often.

Density: Cannabis roots don’t like to work too hard to expand. Soil that becomes too compacted will not be a good growing medium for your weed. You should be able to easily stick your finger into the soil with little resistance. When purchasing soil, a quick test of soil density is to lift different types of soil bags (of equal volume) from different suppliers. Those that feel heavier are probably denser.

pH Level: Cannabis likes soil that is a little on the acidic side. However, since most nutrients will tend to lower the pH level, this is generally not a problem, depending on the pH level of the water you are using. If you intend to purchase potting soil or coco coir, this is not an issue. If you are mixing your own organic soil, it might be worthwhile to invest in a soil pH meter so you can “dial-in” your soil correctly. Different mediums start with different pH levels. For example, coco coir is between 5.2-6.8. When a medium is in this range, it is considered relatively “neutral.”

Best Soil for Growing Marijuana

For beginners, especially indoor growers, your best choice will be to purchase a high-quality potting soil. It is inexpensive, available everywhere, and is very forgiving of errors. Potting soil generally comes without any pests, fungus, etc. in the soil, and so it is safe to use indoors. There are many reputable suppliers available, including Foxfarm, Pro-Mix, and Scott’s.

If you have a little more money in the budget, consider the use of coco coir. It has all the advantages of potting soil, plus excellent drainage and just the right density. It is an appropriate choice for both indoor and outdoor container-based growing. Both Botanicare and Canna are well known for being good quality products.

If you plan to grow outside, consider mixing up your own organic soil. While there is more time and effort involved in getting started, you won’t have to add nutrients to your soil continually. While it will require more effort to find the right recipe for your location, the effort will pay off in wholesome plants and sweet smoking. There are many high-quality organic potting soil mixes you could also consider from well-known suppliers such as Miracle Grow, Pro-Mix, and Foxfarm.

If money is no object, you could also consider a “hybrid” soil such as BioCanna’s Bio Terra Plus, which contains potting soil, coco coir, organic supplements, and a variety of other goodies. I’ve not used it myself but have heard many good things about it.

Soil Tips & Tricks

If you choose to mix your own organic soil, then it will not need any additional amendments because it is already properly prepared. As mentioned, getting the correct formula can be challenging, so be prepared to take some time to get this right.

For potting soil, consider mixing it 80/20 with perlite to make the soil less dense. While this means you will need to water more frequently, it gives the roots plenty of “elbow room” to spread out.

Coco coir doesn’t require perlite, but depending on the manufacturer, it may need to be “pre-rinsed” before use to wash away any accumulated dirt or dust from the manufacturing process. Generally speaking, the better suppliers have already rinsed the product. Coco coir also tends to require more calcium and magnesium than potting soil, so consider adding a bit extra to your regular feeding schedule. As a bonus, you can purchase coco coir in expandable bricks, which makes transport and storage more convenient.

When you are ready to experiment, there are a wide range of soil preparation additives you can consider, including B1 Complex, root enhancers, and soil enzymes.

Container Options

You need someplace to put your weed growing soil! For indoor growing, a 3-gallon container is fairly standard. Larger containers lead to taller plants, which can be a problem indoors. However, if you are willing to use cultivation approaches like a Screen of Green or Supercropping, you could use a bigger container.

For outdoor growing, if not in a garden bed, you will need at least a 5-gallon container, or larger if possible. Your plant will grow very tall and could easily tip over if your container size is too small. Consider weighing down your container by putting a layer of gravel in the bottom before your medium. This will also help with drainage.

Recently, fabric containers (aka air-pots, smart-pots, etc.) have become trendy for both indoor and outdoor growing. They use a technique called “air pruning” to prevent the plant’s roots from circling the inside of the container. This is supposed to lead to better growth, but the evidence is not conclusive.

So, there you have it. Hopefully, our guide has taken some of the guesswork out of choosing the best soil for marijuana growing. The last bit of advice I can offer is to try and limit the different elements, keep things simple, and don’t fall into the trap of always trying something new. Stick with what you know, and I can almost guarantee you will have a great grow.

Happy growing!

Key Points

Avoid non-organic soil supplement with fertilizers, soil from your backyard, or planting outside in the dirt.
Look for high-quality potting soil, organic soil, or coco coir (coconut shell-based soil).
Cannabis plants like room for their roots to expand as well as good drainage – avoid heavily compacting the soil.
Soil pH for Cannabis plants should be on the acidic side – if you can you should measure this before planting your seeds.
House your soil in a 3-5 gallon container.

Jerry Golick

Jerry Golick is a Montreal-based medical cannabis activist and writer. He has been promoting the legal use of cannabis for over 30 years. He is motivated by a core belief in righting the injustices the cannabis prohibition has caused. He has lectured on the topic to diverse groups, as well as assisted physicians in developing educational programs on the subject. His articles have previously appeared on Cannabis Digest, Lift, Cashinbis, and other online websites.

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