Soil. Dirt. Earth. The stuff we grow cannabis plants in. Do you ever think about what makes “dirt” into “soil”? Have you considered how the right type of soil helps to maximize a cannabis plants production? In other words, have you thought about which soil is the best soil to use to grow cannabis plants in for the highest quality yield?
Have you researched the difference between growing outdoors and indoors and how the soil impacts the success of your grow?
There’s quite of dirt to dig through and we’re going to touch on several important topics. We’re really only scratching the surface and there are several topics we’ll uncover which you might want to dig deeper on.
(Editor’s Note: we apologize profusely for this paragraph)
Let’s Get Digging (last one, we promise)
Here are some ways which soil can vary from place to place and, among the categories of soil, type to type:
- Drainage
- Texture
- Water Retention
- Nutrients
- pH Level
Types of Soil
First, let’s talk about the types of soil (credit Wiki):
Sandy Soil is a soil with a high percentage of sand, or large soil It mainly consists of rock particles such as limestone, shale, granite and quartz. Water travels through sandy easily, so nutrients leach out quickly.- Silt is granular material of a size between sand and clay, whose mineral origin is quartz and feldspar.
- Clay is a finely-grained natural rock or soil material that combines one or more clay minerals with possible traces of quartz (SiO2), metal oxides (Al2O3 , MgO) and organic matter.
- Loam is soil composed mostly of sand, silt and a smaller amount of clay. By weight, its mineral composition is about 40–40–20% concentration of sand–silt–clay, respectively. These proportions can vary to a degree, however, and result in different types of loam soils: sandy loam, silty loam, clay loam, sandy clay loam, silty clay loam, and loam. In the United States Department of Agriculture textural classification triangle, the only soil that is not predominantly sand, silt, or clay is called “loam”.
Here’s a summary table:
| Soil Types | Characteristics |
|---|---|
| Sandy Soil | * Large Granular Size * Lower pH * Pro's -Good drainage -Prevents conpaction -Easy to work -High O2 levels * Con's -Dries out quickly -Nutrients wash away -Poor water retention |
| Silt Soil | * Medium Granular Size * Pro's -Contains nutrients -Stabilizes plants -Retains water * Con's -Easily compacted -Poor drainage |
| Clay Soil | * Small Granular Size * Higher pH * Pro's -Stabilizes plants -Provides minerals - Retains water * Con's -Hard to work -Heavy -Poor drainage |
| Loam Soil | *A mixture of all three types of soils * Different ratio's create different characteristics in the loam |
Signs of Good Cannabis Soil
What are the signs of good soil to grow cannabis plants in? Are there things we can look for which will give us a sense of how healthy the soil is?
As most backyard gardeners know, there’s something about good soil which makes the work of potting plants or planting a flowerbed worth it. If you’re growing a veggie garden, then, you also know what “good earth” smells like … the richness of it, the color of it and how it feels in your hand.
There’s no real difference when it comes to soil to grow cannabis plants – you still want the same characteristics you’ve always looked for.
To be more specific: the soil should be dark and rich, loose (you can grab handfuls but some will slip through your fingers) and it should drain well; it can hold water but it drains so that it doesn’t get lumpy or muddy.
As we discussed above, there are different types of soil (sandy, silt, clay and the combination of all three: loam) and (as discussed below) there are amendments to the soil that allow for more oxygen absorption, better root-ball development and more complete drainage.
Nutrient Amendments
And then there are all the nutrient amendments you can work with. These include:
- Bat guano
- Fish meal
- Crab meal
- Bone meal
- Blood meal
- Azomite
- Pumice
- Kelp
- Dolomite lime
- Greensand
- Mycorrhizae
- Leonardite
Soil Amendments
This table is a list of the most common soil amendments used to grow cannabis plants.
| Amendment | Characteristics |
|---|---|
| Perlite | •Perlite is a very common soil amendment. • It is a very light, airy white "rock" and it adds oxygen while increasing overall drainage ability by creating space within the soil. |
| Vermiculite | • Vermiculite holds water much better than perlite, but is not as effective at adding aeration and drainage. • Together, perlite and vermiculite should never make up more than 50% of your soil. |
| Coco Coir | • Coco coir is made from coconut husks. • 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. • If you're adding it to a soil mix as an amendment, you might add 10-30% coco coir. |
| Worm Castings | • Cannabis plants love this stuff! • 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 |
When You Buy a Mix at the Store:
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Don’t Buy “Time Release” Soil
- The issue is: these types of soils are “preloaded” with nutrients that are “wrapped” in a cocoon which slowly dissolves over time. The problem is, there could be too much nitrogen released during the flowering stage, for example, and this would severely stunt the plant’s production.
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Is the Soil “Light”
- What does “light” soil mean? It means it has a light, airy, texture which seems almost fluffy when it’s dry. There are two benefits to this soil: cannabis roots love to push through this type of soil and it will, most likely, drain well, which helps with water management.
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Look and Touch
- If you grab some and form it into a ball, does it stick together and then fall apart with a squeeze? It’s a good sign if the answer is Yes!
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Is the Soil Dark and Rich
- Pretty self explanatory. If the soil doesn’t look and smell right, it probably isn’t.
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Does the Soil Have Perlite In It
- If you see perlite dispersed through the soil like popcorn, then, that is a good sign. It means the soil is intended to have good drainage.
Cannabis is a Weed
Cannabis is often considered a weed (hence the name) because the plant can pop up and thrive in diverse conditions. And we’ve been discussing ways to ensure your working with soil which will grow cannabis plants.
We’ve discussed:
- Proper drainage
- Good water retention
- Beneficial soil amendments
Now, it’s time to talk about soil pH.
Best Soil pH for Cannabis
pH means “potential of hydrogen”. It is used as a chemical scale to specify the acidity or basicity (alkalinity) of a substance (usually a liquid).
Since soil contains water, it also has a pH. Cannabis likes its’ soil slightly acidic, which means, to keep it simple, the ideal pH level is 6; cannabis can also flourish on either side of 6, ranging from 5.8 to 6.3.
What the tradeoff if the soil pH runs outside of this 5.8 to 6.3 range? The plant won’t produce as much, or as high a quality, cannabis as it could.
The magic number is “6”
Ok, so, how do I measure that? The answer is simple, you’ll need a pH tester. You don’t have to spend a lot of money (maybe $10 to $15 online) but you do need at least one. So, spend the money, get the tester and stick it … into your dirt to see where you stand.
Best Soil to Grow Cannabis Plants Outdoors
How are you growing?
If you’re going to grow directly into the ground, you’ll potentially need to augment the natural soil with nutrients, something to give the root-ball room (perlite) and other amendments. A way to determine what the soil is lacking is the “eye-ball” test: does it ‘look’ right? And, to go one sense further, does it smell right?
Again, you’ll know good soil when your hands are in it and the only way to really know what you need in your spot is by trial-and-error.
And, don’t forget the pH meter!
Now, if you’re going to build raised beds and build your soil from scratch, as it were, you’ll want to review your research and make a determination about what type of soil or super soil you’ll want to work with.
There is always a learning curve with any subject and finding the right way to grow cannabis plants in your micro-climate will require some testing to get it right.
Read more about Growing Cannabis Outdoors
Best Soil to Grow Cannabis Plants Indoors
There are several factors to consider with indoor grows soil, primarily: temperature and humidity. We’ve been talking about the learning curves and the trial-and-error of finding the perfect soil to grow cannabis plants in general and now we have to factor in the characteristics of your grow room.
Does your room run hot? How’re you controlling humidity? For example, if you have a hot room which runs ‘dry’ and you put in a very quick to dry soil, your plants might be too thirsty too often.
One of the good things about growing indoors is you can test different kinds of soils in different pots (or sections) of your room and, after just a couple of grow cycles, you should have the (R)oom + (S)oil = (P)erfect Cannabis equation figured out!
Read more about Growing Cannabis Indoors
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