When you decide to try your hand at growing weed, there’s a lot to deal with.
First of all, what strain should you grow? Will you grow indoors or out?
If you’re going to grow outdoors, where can you put your plants so they’ll get the right amount of light? How can they be protected against extreme climate conditions — and nosy neighbors?
If indoors, where can you set up a grow room? What equipment do you need? What about ventilation and humidity? Will it be too hot or too cold?
One key issue may not occur to you until the last minute, though: what type of soil will you need?
Some beginners may decide to jump right into the deep end and try a hydroponic grow. But most start by growing their plants in soil, and they won’t have much success if they choose the wrong growing medium.
Let’s talk about the best soil for cannabis grow.
Why Soil Matters
Some plants can grow in virtually any type of soil. Lettuce, lavender, creeping thyme, and perennial sunflowers are among the varieties that can thrive in poor-quality soil.
Weed plants need soil that can allow their root systems to flourish and provide them with all of the nutrients they need. Not all types of soil can do that, so some simply aren’t a good choice for cannabis.
There’s more to the story, though. The best soil for a marijuana grow depends on several factors; what type of strains you’re growing, where you’re growing them, and the climate (for outdoor plants) or the environment (for indoor grows) all make a huge difference when you’re choosing the optimal type of soil.
Here are some of the details you should know.
Important Factors When Choosing Soil for Cannabis
Before rushing out and grabbing some loam or potting soil for your grow, consider these important factors.
The best soil for marijuana plants is loose and light, not tightly-packed and dense. A light texture allows the plants’ roots to grow and spread properly and makes it easy for crucial oxygen to reach the roots.
The best soil for cannabis will strike a careful balance. It must be able to retain enough water for the roots to access, yet it must also drain well enough that too much accumulated water won’t cause plant damage or death. If the soil gets muddy or remains relatively dry when watered, those are bad signs.
The amount of (or lack of) acid in the soil makes an enormous difference to the health of weed plants. The scale that measures acidity is known as pH. A pH of 7 is “neutral,” while numbers lower than that indicate greater levels of acidity, and higher numbers indicate alkalinity.
Cannabis can only grow properly when the soil’s pH is in the neighborhood of 6.0. If it gets much lower (below 5.8) or much higher (above 6.3), the plants may yield a much smaller harvest — or even die.
You’ll be adding nutrients to the soil throughout the grow, needless to say. But unless you start with soil that has a proper nutrient balance, you may be fighting a losing battle.
Two important factors to look for when you’re starting cannabis plants are soil that contains enough nitrogen to support the plants’ early growth and a good balance of beneficial bacteria and fungi. Most store-bought soils that are appropriate for marijuana plants will have both features.
But what if you’re using natural soil?
Best Types of Soil for Cannabis Grows
You’ll likely be purchasing soil for an indoor grow. If you’re growing outdoors, though, you may want to use natural soil that’s available on your property or the stuff you buy for your vegetable or flower garden. Here’s what to know about both situations.
There are four categories of soil commonly used for growing plants outdoors. Some are better than others for cannabis plants.
This soil is expensive, as you certainly know if you’re a gardener. It’s the best choice, however, because it’s a nutrient-rich mix of the other three types of soils. It strikes the right balance between water retention and drainage.
Silt’s medium-coarse texture provides decent drainage and good water retention, and it has bountiful amounts of minerals and nutrients that weed plants need.
Its texture makes sand easy to work with. But it has a naturally low pH which needs regular monitoring and adjustment, and it doesn’t retain water well, so frequent watering is essential.
The worst soil for cannabis. It drains poorly because of its dense texture, and it has a naturally high pH. Plants could benefit from clay’s natural nutrients, but it’s best used in a loam mix.
There are all sorts of “recipes” designed to let people create their own organic “super soil” for indoor cannabis grows. They involve layering straw, manure, blood, or bone meal and then letting the mixture decompose. The resulting compost is nutrient-rich and ideal for weed plants.
Simple hobbyists or those who are growing for the first time, though, may not want to spend weeks or months creating soil. There are several less time-consuming options.
Home-Made Cannabis Potting Soil
This recipe, courtesy of RoyalQueenSeeds.com, will get you going in a flash as soon as you buy a few ingredients found at any gardening center. You’ll have to adjust the amount of each depending on how much soil you want to create.
- Soak one part coco coir peat (made from coconut husks) in warm water.
- Take two parts compost and remove the largest chunks by putting it through a sieve.
- Mix the coco coir peat with one part vermiculite (a heat-treated mineral).
- Add the compost and ½ cup worm castings, and mix.
This soil will support the growth of your cannabis plants well. But if you don’t want to bother with making your own growth medium, there are several pre-mixed soils designed specifically for weed grows.
Best Packaged Soil for Cannabis
Two cannabis soils are extremely popular among home growers.
- Fox Farms Happy Frog Potting Soil: This soil has all of the essential nutrients, fungi, and bacteria that young weed plants need, as well as the proper pH level. It can be used outdoors or indoors, too.
- Nature’s Living Soil Organic Super Soil: Simply put, “living soil” is a fertile, healthy soil that’s home to a diverse range of natural organisms. This “super soil” theoretically lets you grow cannabis without having to constantly add nutrients because everything the plants need has already been mixed in. That’s often true, but it’s still a good idea to check nutrient levels periodically.
Both products are available online. If you prefer to use more general organic potting soil, it usually will be more than “good enough” for a cannabis grow; the best one to look for is Sungro Black Gold All-Organic Potting Mix which is available at most garden centers.
Best Soil for Cannabis: FAQ
Q: You mentioned that some types of cannabis strains need different soil than others?
A: The biggest difference is whether plants are photoperiods or autoflower. Heavy soil that’s loaded with nutrients will damage auto-flowering plants when they’re young; they do better in a light mix of peat and coco coir.
Q: What about the right soil for outdoor grows?
A: The key consideration is what your climate does to the soil. Hot and dry weather dries out the soil quickly and causes it to crack; frequent watering can undoubtedly help, but choosing a soil that is better at moisture retention is crucial for keeping the plants healthy and alive.
Winston, M. E., Hampton-Marcell, J., Zarraonaindia, I., Owens, S. M., Moreau, C. S., Gilbert, J. A., … & Gibbons, S. M. (2014). Understanding cultivar-specificity and soil determinants of the cannabis microbiome. PLoS one, 9(6), e99641 .