Building Your Own Super Soil

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What super soil actually is

Super soil is a heavily amended organic potting mix designed to supply most of a cannabis plant's nutrients through microbial breakdown of organic matter, rather than liquid feeding. The grower combines a base potting soil with concentrated organic amendments (guanos, meals, minerals, compost), then lets the mix 'cook'—meaning aerobic microbes break amendments down into plant-available forms—for several weeks before use ^[1].

The term was popularized by breeder Subcool (TGA Genetics), whose published recipe in Dank: The Quest for the Very Best Marijuana became the template most growers adapt. The approach overlaps with the broader practice of living organic soil systems, which prioritize a stable microbial community over time.

It is important to note that while growers often claim super soil supplies "most or all" nutrients through microbial activity, the actual nutrient release is variable and depends on microbial populations, temperature, moisture, and amendment quality Weak / limited. Peer-reviewed research on cannabis-specific super soil nutrition is limited.

Why growers use it

The main reasons are practical, not based on yield claims:

• Simpler feeding. Once cooked, you mostly water with plain pH-adjusted water. No mixing nutrient schedules every few days.
• pH buffering. Organic matter and humus buffer pH swings better than inert media Strong evidence^[2]. This reduces the need for constant pH adjustment and helps maintain stability across the root zone.
• Reusable. A super soil bed can be re-amended and reused for years, lowering long-term cost per grow.
• Flavor and aroma reports. Many growers report subjective improvements in flavor and aroma from living soil grows. Controlled comparisons under identical environmental conditions are scarce Anecdote. Treat this as anecdotal until peer-reviewed data emerges.

What super soil does not do: it does not inherently produce bigger yields than a competently run synthetic or hydroponic system Weak / limited^[3]. Peer-reviewed comparisons of organic versus conventional cannabis nutrition are limited, and results are mixed.

When to start

Start mixing 4 to 8 weeks before you plan to transplant into it. Amendments need time and aerobic microbial activity to convert into plant-available nutrients; using uncooked super soil on young plants will almost always cause nutrient burn, especially from high-nitrogen components.

Temperature affects cooking speed significantly. The pile cooks faster at 20–30 °C (68–86 °F) and stalls in cold environments below 15 °C. Check it weekly—it should smell earthy (like forest floor), feel warm in the center during the first 1–2 weeks, and stop heating up before you use it Weak / limited. Do not use it while it is still actively heating or producing ammonia smells; both indicate incomplete breakdown.

How to build it: step by step

This is a representative Subcool-style recipe, scaled per ~1 cubic foot (~28 L) of base soil. Wear a dust mask when handling dry amendments to avoid inhaling particles.

1. Gather a base soil. Use a quality peat- or coco-based organic potting mix with perlite for drainage. Avoid mixes pre-loaded with synthetic time-release fertilizer, which can complicate nutrient availability.

2. Add amendments per cubic foot of base soil:

• 1.5 lb (680 g) high-N bat guano or fish meal
• 1.5 lb (680 g) blood meal or additional fish meal
• 2–3 lb (~1 kg) bone meal or fish bone meal (phosphorus, calcium)
• 1 cup kelp meal (potassium, micronutrients)
• 1 cup dolomite lime (calcium, magnesium, pH buffer)
• 1/2 cup Epsom salt (magnesium)
• 1/2 cup azomite or basalt rock dust (trace minerals)
• 2 tbsp powdered humic acid
• 25–50% by volume good compost and/or worm castings

Quantities vary across published variants; the above is representative, not a strict formula. Adjust based on your base soil's existing nutrient content and your water's mineral profile ^[1].

3. Mix thoroughly. Spread a tarp, layer the base soil and amendments, and turn it like you're folding dough until evenly distributed. Use a shovel or garden fork to ensure no pockets of undissolved amendments remain.

4. Moisten and pile. Water until the mix is damp but not dripping (squeeze test: a clump holds together, no water runs out). Pile it into a tote or trash can with a loose-fitting lid—not airtight. Airtight conditions promote anaerobic decay, which produces ammonia and sour, putrid smells.

5. Cook for 30–60 days. Turn the pile every 1–2 weeks. The center will warm up during the first 1–2 weeks (indicating active microbial decomposition), then cool. When it stops heating noticeably and smells sweet and earthy, cooking is complete Weak / limited. This typically takes 4–8 weeks depending on temperature and pile size.

6. Use it layered, not pure. Most growers fill the bottom one-third to one-half of a finishing pot with cooked super soil and top with plain organic potting soil, so roots grow into the amendment layer as the plant matures. Seedlings and clones go into the plain top layer to avoid nutrient burn.

Common mistakes

• Planting seedlings directly in pure super soil. Almost guaranteed nitrogen burn and stunted growth. Always layer it, or transplant only well-established vegetative plants into pure super soil.
• Skipping the cook or rushing it. Fresh amendments, especially blood meal and high-N guano, will scorch roots and produce harsh ammonia smells. Wait until the pile cools and smells earthy.
• Sealing the container. Anaerobic conditions produce ammonia and sour, putrid odors. Use a breathable cover (e.g., loose-fitting lid, burlap) and ensure airflow.
• Adding bottled nutrients on top of super soil. You usually don't need them, and salt-based feeds can suppress the microbial life you spent weeks building Weak / limited^[2]. If you feel the need to boost during heavy flowering, use low-salt organic supplements and monitor for salt burn.
• Micromanaging pH with liquid pH-down every watering. Let the dolomite and organic matter buffer it naturally. Use a slurry test or pH meter to confirm soil pH is in the 6.2–6.8 range, but avoid constant adjustments that disrupt buffering.
• Ignoring pests in the soil. Hot, moist organic mixes attract fungus gnats and can harbor soil-borne pathogens. Top-dress with a thin layer of dry mulch (e.g., rice hulls) and consider beneficial nematodes or Bacillus thuringiensis israelensis (Bti) if gnats appear Strong evidence^[4].

Related techniques

• Growing in 5 Gallon Pots with Living Soil — scaling up the super soil concept for container grows.
• Growing in 15-Gallon Pots with Living Soil — larger-volume no-till or amended-soil approaches.
• Outdoor Soil Preparation — building native or raised-bed soil for outdoor grows using similar organic amendment principles.
• pH Management in Cannabis Cultivation — understanding how super soil buffers pH and when adjustment is necessary.
• Coco Coir Growing — a simpler inert-media alternative if super soil sounds like too much prep work.

If you have never grown cannabis before, start with a quality bagged organic soil and light bottled feeding, then graduate to building your own super soil on your second or third grow once you understand basic plant nutrition and watering rhythms.

Sources

How this page was made

Related

• Coco Coir Growing — Soilless growing medium offering root oxygenation and nutrient control for cannabis cultiv...
• Growing Cannabis in 15-Gallon Pots with Living Soil — A home-scale no-till organic system using microbial-active soil and topdressing.
• Growing in 5 Gallon Pots with Living Soil — A compact living soil system for indoor growers: biology, amendments, and practical techni...
• Outdoor Soil Preparation — Testing, amendment, and biological building before transplant for stronger roots and less...
• pH Management in Cannabis Cultivation — Control nutrient availability by maintaining pH in your growing medium.
• Slurry Test for Soil pH — Direct measurement of soil pH by mixing a sample with water and reading the suspension.