What is super soil?

Short answer

Super soil is a heavily amended organic soil, rich in compost, worm castings and slow-release amendments, cooked moist for a few weeks and intended to feed a cannabis plant through most of its life with plain water. It is usually layered, with a strong layer low in the pot and milder soil on top. Grower practice: popular and workable, but no controlled cannabis trial has compared it with other systems.

Why

Organic amendments don't feed the plant directly. Soil organisms break them down and release plant-available nutrients, and that release depends on moisture, temperature and biology ^[1]^[3].

Cooking the mix starts that breakdown before planting. A freshly amended mix can be "hot", releasing ammonium and salts fast enough to burn seedlings.

Layering solves the seedling problem. Young roots grow in mild soil and reach the strong layer only when the plant can use it.

The weakness is precision. Release is slow and hard to adjust, and late-flower demand can outrun it. Organic feeding can still give high yields when nitrogen supply is high enough ^[2], which is why many growers top-dress in mid flower.

The plant mostly doesn't care where its ions come from. Claims that super soil makes better-tasting buds are Grower practice, untested in controlled trials.

The numbers

Item	Typical
Container	25–100 L (7–25 US gal)
Strong layer	Lower half to two-thirds of the pot
Mild top layer	Top third, plain potting mix
Cook time	2–4 weeks, moist and warm
Water pH	As-is unless very alkaline (root zone about 6.3–7.0)
Soil temperature	18–24 °C (64–75 °F); biology slows below about 15 °C
Top-dress	Mid veg and early-to-mid flower if plants pale

What to do

Mix base soil with compost, castings, perlite and a balanced organic amendment package.
Moisten, cover and cook for 2–4 weeks.
Fill the pot with the strong layer, then top with mild potting mix.
Plant, water with dechlorinated water and mulch the surface.
Watch lower leaves from mid flower; top-dress if they pale early.

Common mistakes

Planting seedlings straight into the hot layer.
Small pots of super soil that run out by week 4 of flower.
Flushing before harvest. That's a Myth that costs yield; keep watering normally.

Full article: Living soil
Answers: reusing soil · do mycorrhizae help · kitchen scraps as fertiliser
Terms: super soil · living soil · top-dressing

Follow-up questions

What is the difference between super soil and living soil?

Super soil and living soil overlap, but the emphasis differs. Super soil is defined by a strong amendment recipe built to feed one plant for one run with water only. Living soil is defined by managing soil biology over many runs: a large container or bed, no-till, mulch and top-dressing between crops. A super soil reused and mulched gradually becomes a living soil.

Can I plant seedlings directly in super soil?

Don't plant seedlings directly into the rich layer of super soil, because the high nutrient load can burn them. Fill the top third or so of the pot with milder potting mix, or start seedlings in a small pot of plain mix and move them once roots are established. By the time roots reach the strong layer, the plant is big enough to use it.

Do I need to pH water for super soil?

You generally don't need to pH-adjust water for super soil. Compost and organic matter buffer the root zone, and plants and soil biology work around a near-neutral pH of roughly 6.3–7.0. Use dechlorinated water as it is unless it is very alkaline. Adjusting water to pH 6.0 out of habit, as for hydro, is a common mistake in organic soils.

Sources

USDA Natural Resources Conservation Service. Soil health principles (minimise disturbance, keep soil covered, maintain living roots, maximise biodiversity). nrcs.usda.gov/conservation-basics/natural-resource-concerns/

Caplan D, Dixon M, Zheng Y, 2017. Optimal rate of organic fertilizer during the vegetative-stage for cannabis grown in two coir-based substrates. HortScience 52(9):1307–1312. doi.org/10.21273/HORTSCI12401-17

Raviv M, Lieth JH, Bar-Tal A (eds), 2019. Soilless Culture: Theory and Practice, 2nd ed. Elsevier (organic substrates and compost chapters). doi.org/10.1016/C2015-0-01807-5