When it comes to growing cannabis in soil, it’s imperative to choose or create a blend that will allow your plants to perform their best. Soil, at a basic level, is defined as the topmost layer of earth in which plants grow, a mixture comprised of organic remains, clay, and rock particles.
But when perfecting an environment for high-quality cannabis, there is much more to consider. Soil varies in a number of common ways, such as:
- pH level
- Water retention
- Nutrient makeup
Check out these additional resources for more info on soil and planting:
Traits of quality soil for cannabis
Soil is generally described as having a mixture of sandy, silt, or clay textures. Most of us have gotten our hands dirty before—and while playing in the dirt, you’ve likely noticed these variations.
The texture directs the overall structure of the soil, so when it comes time to put your seeds in the ground, be mindful of its attributes.
- Large granular size
- Lower pH
- Pros: Good drainage, prevents compaction, easy to work with, high oxygen levels
- Cons: Poor water retention, dries out quickly, nutrients get washed away
- Medium granular size
- Pros: Naturally fertile (contains nutrients), retains water, stabilizes plants
- Cons: Poor drainage and easily compacted
- Small granular size
- Higher pH
- Pros: Provides minerals, retains water, stabilizes plants
- Cons: Poor drainage, heavy soil, hard to work with
While some plants thrive in their native soils, which are dominated by one of the compositions listed above, cannabis plants are best grown in soil that includes a combination of those three textures and properties. This mixture is known as loam.
What does loam soil look like?
The best way to identify loamy soil is by touching it. How does it feel? Sandy soil should be difficult to compact while clay should compact into a tight ball that won’t crumble. When squeezed, loamy soils should form a loose ball that will hold its structure momentarily before breaking apart in large chunks.
Here are some qualities of loam soil:
- Mixture of sand, silt, and clay
- Near neutral pH
- Pros: Drainage, water retention, naturally fertile, easy to work with, nutrient retention, supports microorganisms, high oxygen levels
- Cons: Can be costly
Most potting soils used in gardening are loam soils. If you’ve ever worked with potting soil, you’ll know that its composition is rich and diverse, and it looks dark and hearty. Beyond texture and color, the soil should smell alive and rich.
Buying the right soil for cannabis
While shopping for soil, you might be overwhelmed by the options available at your local garden store. You now know that most of these soils will be loamy, but why are there so many different types?
Consider the soil type as the basic structure of your soil. From there, look at nutrients, microorganisms, and other amendments that improve your soil. Your choices will be flooded with words like:
- Worm castings
- Bat guano
- Peat Moss
- Fish Meal
- Bone Meal
- Glacier rock dust
- Plant food
These are just some examples of amendments that are commonly listed on different types of soils. Heavily amended soils will have long lists that break down all organic nutrients they contain. Some companies create soils that offer a great structure with base nutrients, but allow you to fill in the gaps as you desire.
For most first-time gardeners, we recommend buying a quality potting soil that will provide your plants with enough nutrients to get them through most of their growth cycle without having to add many amendments or liquid nutrients. Below are two soils we recommend for beginner cultivators.
Recommended soils for cannabis
Depending on where you live, you’ll have a different experience finding a quality soil mix that fits your needs. Generally speaking, my advice is to visit your local nursery or grow store and talk to the experts. If you’re shy about mentioning cannabis, ask for a rich soil suitable for tomatoes, which thrive in similar soil.
It also should be noted that the soils below are not recommended for starting your plants. Ready-to-grow soils contain lots of organic nutrients that are too rich for a seedling. These soils are made so that you can transfer starts, but seedlings should be grown in a simpler potting soil.
Produced in Colorado by Miller Soils, Red’s premium blend is your one-stop shop for growing cannabis. This soil is ready to use, containing a complex mixture of amendments. The biochar provides a quality habitat for microbes to populate, while also aiding in water and nutrient retention.
You can hit the ground running with this blend because it has a complex food web already active in the soil, waiting for your roots to enjoy. You won’t need to worry about feeding your plants more than a few times, if at all.
A notable soil produced by Aurora Innovations, the Roots Formula 707 organic blend offers a different approach to ready-to-pot soil. With a peat moss base, it was designed to aid in water retention, and it backs off on amendments so you can add topsoil or liquid feed plants at your own discretion. It’s recommended that you wait 10-14 days before adding nutrients to plants in this soil.
Designed for large-scale outdoor growing, Formula 707 is widely available and suitable for indoor gardens and small-scale operations as well.
This post was originally published on January 10, 2018. It was most recently updated on June 28, 2020.