Super soil is a heavily amended organic potting mix that feeds a cannabis plant from transplant through harvest with nothing but plain water. You start with a light, airy base mix, blend in organic meals, mineral powders, and rock dusts, then let the whole pile sit for four to eight weeks so the microbes break the amendments down. Once it is cooked, you layer it into the bottom of the pot and top off with a plain base mix. That is the entire method.
Cannabis Super Soil vs Synthetic Nutrients: A Comparison Review
What actually goes into a super soil
Every version of this mix comes down to four components, and the ratios matter more than the brand names.
how to make supersoil for cannabis plants
- Base: a peat-based or coco-based potting soil with little to no fertilizer in it. This is the bulk of the pile.
- Aeration: perlite, pumice, or rice hulls. Around 20 to 30 percent of the finished volume keeps roots from drowning.
- Humus: worm castings, finished compost, or both. This is the engine that drives nutrient cycling.
- Amendments: the meals, liming agents, and rock dusts that supply slow-release food for months.
The recipe (roughly 50 gallons of finished mix)
Base mix
- 25 gallons quality organic potting soil or a peat and coco blend
- 10 gallons worm castings
- 10 gallons coarse perlite or pumice
- 5 gallons finished, screened compost
Amendments
- 2 cups blood meal
- 3 cups bone meal
- 3 cups bat guano (high phosphorus type)
- 2 cups kelp meal
- 2 cups alfalfa meal
- 1 cup crab shell meal or neem seed meal
- 1 cup dolomite lime
- 1 cup gypsum
- 1 cup soft rock phosphate
- 1 cup greensand
- 1 cup azomite or glacial rock dust
That is a fairly standard starting point. Some growers cut the blood meal and lean harder on crab shell and alfalfa for a gentler nitrogen release. If you live somewhere humid, skip the blood meal, because it draws pests.
how to make supersoil for cannabis plants
How to mix it
- Spread a tarp on a hard surface, or use a large tote or kiddie pool.
- Dump in the base soil, castings, compost, and aeration. Mix thoroughly with a shovel or by rolling the tarp corners.
- Sprinkle the dry amendments across the top a cup or two at a time. Do not pour them in one spot.
- Turn the pile three or four times until you cannot see streaks or clumps of any single amendment.
- Add water slowly while turning. You want it evenly moist, like a wrung-out sponge. Squeeze a handful; a drop or two should come out, not a stream.
Then let it cook
Cooking is not optional. Fresh amendments are raw and hot, and planting into an uncooked mix burns seedlings and stalls clones. Put the pile in a container or covered tote, keep it between roughly 65 and 80 degrees Fahrenheit, and leave it alone for at least 30 days. Sixty days is better. Turn it once a week and check moisture, because it will dry out at the edges. A white fungal fuzz on the surface is normal and a good sign. Recheck moisture every time you turn it.
Using it in the pot
Super soil is layered, not blended into the whole container. The bottom of the pot gets the hot stuff, the top gets the mild stuff, and the roots reach down into the food as the plant grows into it.
- Fill the bottom third to half of the container with cooked super soil.
- Top the rest off with plain base mix or a light seedling mix.
- Plant the transplant into the plain layer only.
- Use 7-gallon pots at minimum. Ten to 15 gallons is where this method really shines, because more soil means more buffer.
Run one plant per pot unless you are working with a very large container. Two plants fighting over the same root zone will strip it faster than you expect.
Watering and pH
Water only, and water evenly. Tap water with chlorine or chloramine will knock back the microbial population, so let it sit out or run it through a carbon filter. Aim for a water pH between 6.2 and 6.8. Do not chase runoff numbers the way you would in coco, since a living soil buffers itself. Let the pot dry back a bit between waterings rather than keeping it saturated, and feed the soil occasionally with a compost tea or worm casting slurry if the plant looks hungry late in flower.
Re-amending for a second run
Good super soil gets better the second time. After harvest, pull the root ball, break the soil back into a pile, and re-amend at roughly half the original rates. Add fresh castings and aeration too, since those break down over a cycle. Cook it again for three to four weeks before reuse. I get two or three solid cycles out of a batch before I rebuild it from scratch.
Mistakes I see most often
- Planting before the mix cooks. This is the single most common failure.
- Filling the whole pot with super soil, then wondering why the seedling is fried.
- Adding bottled synthetic nutrients on top of a living soil and throwing off the biology.
- Skipping aeration, which leads to compacted, waterlogged roots.
- Using too much lime and pushing pH alkaline, which locks out iron and manganese.
- Letting the pile dry out during the cook period, which stalls the breakdown.
One last thing: check your own state's rules on home cultivation before you mix anything. Legality varies widely, and a good recipe does not help if the grow itself is not allowed where you live.