Soil, in the strict sense, is natural earth: mineral particles (sand, silt, clay) plus organic matter, water, air and living organisms. In indoor cannabis growing, "soil" is used loosely for bagged potting mixes and composts as well, most of which are actually soilless peat- or coco-based blends with added nutrients.
In practice
Soil and soil-like mixes hold nutrients on their exchange sites and in organic matter, buffer pH changes, and host microbes that release nutrients over time. That makes them forgiving for beginners: missing a feed or a small pH error does less damage than in hydro. The typical target pH range is about 6.0-7.0. Growth is generally a little slower than in well-run hydro or coco, and feeding is less precise.
Garden soil on its own compacts in containers and drains poorly; mix it with compost and aeration (perlite, pumice) or use a purpose-made potting mix.
Don't confuse with
- Soilless mix: peat, coco or bark based, no mineral soil; often called "soil" on the bag.
- Living soil: soil managed specifically for biology, usually reused over many cycles.
Potting mix is a manufactured container medium, usually peat or coco with perlite, lime and starter fertiliser, designed to drain and hold air better than garden soil.A soilless medium contains no mineral soil, such as peat, coco, rockwool or perlite blends, and relies mostly on the grower to supply nutrients.pH measures how acidic or alkaline a solution is on a 0–14 scale; in growing it controls nutrient uptake, with soil best near 6.0–7.0 and hydro 5.5–6.5.The pH scale runs from 0 (strongly acidic) to 14 (strongly alkaline) with 7 neutral; it is logarithmic, so each whole unit is a tenfold change in acidity.Coco coir is a growing medium made from processed coconut husk, prized for holding water and air at once; it binds calcium and magnesium unless buffered.Runoff is the water or nutrient solution that drains out of the bottom of a container after irrigation; growers test it to see what is happening in the root zone.Perlite is a light, white, puffed volcanic glass added to growing mixes to increase drainage and air space; it is chemically inert and holds no nutrients.Living soil is an organic growing medium managed to sustain an active soil food web, so microbes and invertebrates release nutrients and the soil is reused across cycles.Super soil is a heavily amended organic soil mix, rich in compost and slow-release amendments, intended to feed a plant through most of its life with only water.Cation exchange capacity (CEC) is a medium's ability to hold positively charged nutrients such as calcium, magnesium and potassium on its surfaces and release them later.
