The marijuana seed breeder and YouTube star Subcool long ago popularized a recipe for making very fertile soil for marijuana growing. He called it supersoil, and claimed that if you grow in supersoil, all you’d need do is water your plants with pure water and not have to worry about adding extra fertilizers.

I do outdoor and indoor marijuana growing and prefer pure hydroponics such as rockool, coco coir, and deep water culture, but when I’ve done remote outdoor growing or had access to private land so I could use huge 100-gallon grow pots, the following supersoil recipe has served me well. This recipe is for 100 gallons of supersoil, and you can scale it up or down depending on how much soil you need.

You need to start by getting 12 cubic feet of high-quality base soil. This is harder to find than you might think. Many of the major soil brands sold in hydroponics stores and elsewhere come with built-in fertilizer loads and/or pests and diseases. Ask your hydroponics supplier for the best soil in the store, but only after you’ve told them you intend to heavily amend the soil to make supersoil.

Another thing to know is that after you mix your supersoil you must let it sit and age for 8-12 weeks before you use it. This can be a hassle, but you must give the organic and natural substances in the soil time to integrate, decompose and become bioactive before you put plants into your supersoil.

Supersoil Recipe

Here’s my recipe for 100 gallons of supersoil:

To 12 cubic feet of quality base soil add the following:

1 – 30lb. bag of Worm Castings
2.5 lbs. of Fish-based Bone Meal
5 lbs. of High Phosphorus Bat Guano
5 lbs. Blood Meal
2.5 lbs. Regular Bone Meal
3 cups of Oyster Shell
3 cups of Kelp Meal
3 cups of Alfalfa Meal
3/4 cup of Epsom Salt
1 cup of Gardening Lime
2 cups of Azomite
3 TBS of powdered Humic Acid

I also add 1-2 cubic feet of super coarse perlite to the mix, depending on the conditions I’ll be growing in. For example, if I’m growing outdoors in a high-rainfall area where soil would tend to get waterlogged from excessive rain, I add more perlite than if I’m growing in a low-humidity, low-rain area such as Southern California. Coarse perlite is the only kind you should get. It breaks up the soil and creates a web of aerated pockets for roots, oxygen and water, which are extremely beneficial for root health.

Speaking of root health, be sure to add in mycorrhizae, which are beneficial microbes that colonize the root zone. They protect roots, and expand the size and function of the root mass. Contact the company in the link I just gave you, and ask them how much you should use for the amount of soil you’re mixing.

Most growers mixing supersoil do it in very clean garage, shed, or other controlled space where pests, diseases and excess moisture can’t contaminate your soil mix . Some cannabis growers hand mix using shovels, others dump all the recipe components into cement mixers. You definitely want all ingredients to thoroughly break down mechanically so there are no clumps and they’re all integrated together with 100% blending.

After you mix your supersoil, cover it tightly with a couple of tarps and let it sit for 8-12 weeks. At week nine or ten, plant a low-value plant in it and monitor the plants’ performance. You’re looking for signs of overnutrition or undernutrition. If you followed this recipe properly and used high quality components, your plants will thrive.

Supersoil is designed to run out of nutrition during the last 2-3 weeks of bloom phase. The deprivation can take the place of marijuana flushing, a topic we’ve discussed elsewhere on this site. After the on-board nutrition in the soil is depleted, the cannabis leaves will turn autumn-colored and start to die because your marijuana plants are using up the nutrients stored in them.

If your bloom phase plants still have a ways to go and you’re seeing leaf color changing that indicates the soil is depleted, I recommend using a quality organic fertilizer like Iguana Bloom and a supplement called Nirvana administered during watering until about eight days before harvest. I also like to use Bud Candy carbohydrates booster administered via watering during the entire bloom phase.

Soil growing isn’t as  100% predictable or scientifically controllable as hydroponics growing, but it’s easier…as long as you mix your own quality supersoil using the recipe I just shared with you. Please watch the embedded videos so you have enhanced knowledge about making supersoil for marijuana growing, and enjoy the big fat buds your soil-grown plants will produce for you!