A potting mix is a blended container medium. Most are soilless despite the name "potting soil": a base of peat, coco or composted bark, an aerating component such as perlite or pumice, lime to set the pH, often a wetting agent, and a starter charge of nutrients. Some add compost, worm castings or slow-release fertiliser. They are designed for containers, where native soil would compact and waterlog.
In practice
A good cannabis mix drains freely, has visible perlite or bark, smells earthy rather than sour, and is not heavy or sticky. "Lightly amended" mixes feed seedlings and young plants for about two to four weeks before liquid feeding is needed; "hot" mixes rich in organic nutrients can burn seedlings. Check the pH is roughly 6.0-7.0. Mixes for seed starting are finer and lower in fertiliser.
Many growers add extra perlite (20-30%) to standard bags to increase air space.
Don't confuse with
- Garden soil: native mineral soil; poor in containers on its own.
- Super soil: a heavily amended organic mix designed to feed through most of the grow.
A soilless medium contains no mineral soil, such as peat, coco, rockwool or perlite blends, and relies mostly on the grower to supply nutrients.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.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.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.A seedling is a young cannabis plant from emergence of the cotyledons until it has several sets of true leaves, typically the first 2-3 weeks.An organic fertiliser supplies nutrients from plant, animal or mineral-rock sources that soil microbes must break down into ions before roots can absorb them.Air-filled porosity is the share of a container's volume that holds air rather than water after it has drained, a key factor in root oxygen and overwatering risk.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.In cannabis growing, soil means a living, organic-rich growing medium, either natural earth or a bagged mix, that supplies some nutrients and buffers pH and feeding mistakes.Peat is partially decomposed sphagnum moss from bogs, the base of most potting mixes; it holds water and nutrients well but is acidic and needs lime.
