There are two primary mistakes made by novice marijuana growers: over watering and providing too many nutrients. While the first problem is easily solved by simply allowing your soil to completely dry out before watering again, the second is a bit trickier to fix. You’ll need to create the perfect initial nutrient balance within your soil. Starting with great soil is an easy way to minimize the need to pump your plant full of additives and chemicals along the way. In this Super Soil segment, we’ll tell you how to make the best soil for marijuana.
What is the best soil for marijuana?
“To me there’s nothing like the flavor of properly grown organic cannabis: the subtle flavors and aromas created when using Mother Earth is overwhelming to the senses when done properly.”
Yet, what is the best soil for the cannabis plant? In its natural environment, marijuana may not actually be very picky. A relative of the Humulus (hop) and Celtidaceae (hackberry) families, cannabis plants are thought to grow fairly well in soil that has been disturbed either by natural disaster or human interference.
By “grow well”, we don’t mean produce a fantastic crop. Rather, their fast growing, weed-like nature has given the herb an evolutionary advantage. They can pop up, thrive, and crowd out toxic plants when they’re mature. A true ditch weed.
But, to produce a great marijuana crop, you’ll need to put in some effort to ensure the plant is able to create ample amounts of much-desired THC and other cannabinoids. Here’s what it likes:
- A lot of nitrogen in vegetative phase
- Less nitrogen, more phosphorus during flowering phase
- A PH range between 5.8 and 6.3. About 6 is the best. It can tolerate PHs a little higher or lower than this, but you won’t see as nice of a crop
- A balanced ratio of soil fungus to bacteria. Because marijuana prefers slightly acidic soil, it may be a little on the fungal side
Both terpenes and cannabinoids are consolidated secondary metabolites. These are compounds that the plant produces in order to communicate with other plants, attract desirable insects, defend itself from predators, and protect against diseases. To produce these metabolites, the herb needs access to a nutrient diverse and high-quality growing medium.
To help you pick the optimum growing medium for your herb, here’s everything you need to know about the optimum soil for marijuana.
Premixed organic brands
When selecting your soil, a good rule of thumb is to err toward mixes that contain a diverse amount of ingredients. Select products that contain natural fertilizers like worm castings, bat guano, or fishmeal. Ideally, if you begin with a strong starting soil and the right natural nutrients you won’t need to splurge on extra products like PH fixers and excessive fertilizers throughout the process.
Here are a few popular mixes available at your local grow shop:
Local mixes are fresh and typically contain organisms that are vital to your region’s specific ecosystem. While the brands listed above are fairly reliable, connecting with a local farmer or soil distributor can be extremely beneficial. The overall freshness of the product can kick your plants off to a great start with highly concentrated and readily available nutrients. Just make sure to get the details of what went into the soil ahead of time.
Purchasing fresh, properly made local compost is another must for getting the most out of your plants. The next segment of Super Soil will dive into compost teas and why great compost is so important to producing top-notch plants. Coco-based soils with added mycorrhizae fungus are always a good start.
Roots Organic potting mix is generally thought to be a high-quality soil designed for optimal cannabis yields. Containing a hearty dose of worm castings and bat guano (natural manures), Roots has plenty of nice natural fertilizers mixed right in. Back in 2014, The Dude Grows Show gave a review of the product. The Dude explains:
“Good potting mix, in my opinion. I like the ingredients, it yields well, if you’re planting into this potting mix you don’t need to use any fertilizer for like two weeks at least. Straight up what’s in there is good. Maybe some enzymes, some beneficial microbe plant-stimulant turbo pack like Recharge.”
Coco fiber, course peat moss, perlite, pumice, composted virgin forest material, worm castings, bat guano, kelp meal, fish bone meal, soybean meal, greensand, alfalfa meal.
This coco-fiber based soil was designed with the intention of rebuilding garden soil “from the bottom up.” This coconut-based soil mix was created in Humboldt and contains absolutely no peat moss. They also treat all of their soils with compost tea prior to packaging. In an interview with CannaInsider, representative Michael Beck tells audiences:
“There are so many packaged soil products out there that are made with ingredients that we consider inferior to building. We saw the writing on the wall moving toward a sustainable, functional alternative to those products.”
Contact Royal Gold for more information on their ingredients.
FoxFarm Ocean Forest is another product commonly used by growers. It’s typically readily available throughout the U.S. Many people add perlite to cut up the mix a bit. This is another Humboldt Organic product. The manufacturer advertises that it’s safe to use right out of the bag and good for seedlings.
Composted forest humus, sphagnum peat moss, Pacific Northwest sea-going fish emulsion, crab meal, shrimp meal, worm castings, sandy loam, perlite, bat guano, granite dust, Norwegian kelp, and oyster shell (for pH adjustment).
Mixing your own soil
Several top growers and seed companies have published great recipes for mixing the perfect high-quality soil. All soil mixtures start with a perfect base, so be sure to do your research or invest in one of the products mentioned above to ensure that you begin the process right.
The recipe below is adapted from TGA Subcool Seeds with added explanations of what each product actually does for the plant. The original recipe was published in High Times. This recipe was chosen for its popularity and highly successful track record. Unfortunately, his recipe is quite large. If you’re a casual home grower, you may want to scale down. For more tips, be sure to check out all that TGA has to offer.
This soil must be mixed up well before you can use it. For best results, put down a large tarp somewhere outside. Mix well with a rake. To begin to build some microbes and to let nutrients absorb into the soil, you need to “cook” the mixture for up to 30 days. You cook it by letting it sit outside in the sun, preferably under a black tarp or in a closed garbage container. Before sealing your soil up, moisten it with water.
Subcool advises that you don’t plant seedlings in this super-charged soil. Because it’s fertilizer rich, it may burn them. Rather, layer this soil on the bottom of your raised bed or container. Then add a layer of regular base soil, followed by some sprinkles of the fertilizing soil on top.
The best soil for marijuana recipe
8 x 30lbs bags of high-quality organic potting soil
Recommended amount: 25 – 50lbs (because this stuff is so nutritious, the more the better).
Worm poop is gardening gold. Properly known as “worm casts”, what worms leave behind is actually vital to the soil food web and is one of the key substances to maintaining healthy, nutrient-dense soil for your plants. To quote from Sustainable World Radio:
“Research has shown that fresh earthworm casts are five times richer in available nitrogen, seven times richer in available phosphates, and 11 times richer in available potash than the surrounding upper six inches of soil. […]
Plant roots often seek out available earthworm casts. They follow the worm Burroughs and feed on the nutrients in the available vicinity even if it means that the roots have to grow upward.”
While growers often spend a significant chunk of change on fertilizers throughout the grow cycle, adding worm castings to your soil inundates them with the vital, natural nutrients they most desire.
Kelp and/or humid acid
Recommended amount: 2 tablespoons humic acid or 1/4 cup kelp meal per five gallons
Marijuana growers are very smart gardeners. There are a lot of things that growers do to increase their yields that actually helping to build healthy soil microbiology. Adding kelp meal and humic acids are some of these tasks. Both of these natural products are fungal foods. The interaction between your plants roots and soil fungus helps the plant produce the nutrients it needs to thrive.
Kelp also adds a significant amount of potassium and copper to your soil mix.
Recommended amount: 5lbs
This is another manure product. Bat guano is another high-nitrogen product. As Westword’s Dear Stoner explains:
“For organic growers who are trying hard to steer clear of heavy metals and petrochemicals in their buds, guano is the choice. Guano is relatively naturally balanced, with appropriate levels of nitrogen, phosphorus and potassium.
Some (including this stoner) would go so far as to say that bat guano is the best fertilizer to use, as it’s natural and doesn’t leave behind any chem-y flavors if the bud is flushed properly.”
Recommended amount: 3lbs (or 10lbs for every 100 square feet)
As its name suggests, rock phosphate is a natural fertilizer that ups the phosphorous content in your soil. It’s a clay derivative and is often combined with bone meal and azomite for a truly nutrient dense combination. As Gardening Know How explains:
“These nutrient-rich fertilizers work with the soil rather than against it as chemical fertilizers do. The nutrients are then made available to plants at a steady and even rate throughout the growing season.
Flowers love an application of rock phosphate early in the season and will reward you with big, vibrant blooms.”
It’s also a natural way to deter pests and lends to a rich flavor.
Recommended amount: 5lbs
If you’re vegan, you might want to stay away from this one. Bone meal is a fine powder made up of ground animal bones. This additive is a nice way to get some additional phosphorous and calcium to your plants. An abundance of phosphorus is especially important once your plant has reached flowering phase. To again draw from Gardening Know How:
“Using bone meal will help your flowering plants, like roses or bulbs, grow bigger and more plentiful flowers.”
As a flowering herb, the added phosphorus from bone meal helps your plant produce buds that are nice and big.
Recommended amount: 5lbs
Blood meal is yet another source of nitrogen. It’s also not vegan/vegetarian-friendly. Blood meal is made from the dried blood of slaughtered animals, most predominantly cows. Though the idea behind the fertilizer is a little unpleasant, its well-known natural gardening product. Because it’s so nitrogen lush, it will help produce extensive growth during the vegetative phase.
Dolomite (sweet lime)
Recommended amount: 1 cup
Dolomite lime adds calcium and magnesium to your soil. Like rock phosphate, dolomite is also a kind of mineral rock. It’s used to counteract mineral leaching. It also helps keep the soil from becoming too acidic. Be careful not to add too much, though. It has high calcium to magnesium ratio, and you may risk adding too much magnesium to your plants.
Azomite (trace elements)
Recommended amount: 1/2 cup
Azomite is a brand of trace minerals. It’s mined from volcanic rock and contains over 70 minerals and trace elements. This particular brand is mined in Utah and is used to re-mineralize soil. The product contains everything from gold, silver, and selenium to potassium, choline, copper and calcium. Adding a few trace elements into your soil increases the diversity of nutrients available to your plant.
There are also ways to increase the availability of these nutrients through cultivating healthy soil microbiology. This will be discussed in our next segment in this series.
Recommended amount: 3/4 cup
A lot of people use Epsom salt to increase magnesium in their soil. As mentioned earlier, you want to be careful not to add too much. You don’t want to over do it with the magnesium. However, if your plant is showing signs of a magnesium deficiency, this is a very quick and easy way to add some back in. Magnesium is crucial to the absorption of other key nutrients, like nitrogen and phosphorous.
All about microbes
Subcool’s soil mixture is definitely a good one. As is probably obvious by the various additives in this recipe, this soil is extremely nutrient-rich. It’s chuck full of natural fertilizers and makes it easy on the plant to have its favorite nutrients right at its root tips, so to speak. Many of the extra or leftover additives can then be diluted with water and sprayed on during the grow cycle as fertilizer.
If there’s one downfall to this recipe, it’s that it relies heavily on organic additives over encouraging microorganism growth. In a plant’s natural environment, they get vital nutrients from synergistic interactions between the plant and other organisms in its ecosystem. Plants photosynthesize sunlight into sugars, and these sugars are in turn secreted by the roots. This is a much more conscious process than commonly believed.
A plant can make an extremely wide variety of sugars and secrete them to attract specific types of bacteria and microorganisms to its roots. These bacteria then eat these sugars, called exudates. Through the bacterial metabolic process, essential nutrients like nitrogen are created for the plant to use. Yet, nitrogen isn’t the only nutrient created through this process. This is how much-needed vitamins and trace minerals make it into your plant.
In our next Super Soil segment, we’ll go into detail on how to use these microorganisms to your advantage. Coupled with nutritious soil, staying smart with your dirt ecology will not only give you great yields but will produce an incredibly potent and nutritious plant. This will particularly be of interest to medical growers and those interested in putting the entire marijuana plant to use. So, stay tuned!
Do you have a favorite soil recipe to make the best soil for marijuana? Care to share it with others? Drop us a line on social media or in the comments below.
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