Soilless growing uses a substrate with no mineral soil in it. Common soilless media are peat moss blends, coco coir, rockwool, perlite, pumice, bark and clay pebbles, used alone or mixed. Some (peat, coco) have a cation exchange capacity and hold nutrients; others (rockwool, perlite, clay) are nearly inert.
In practice
Soilless media are lighter, cleaner and more consistent than garden soil and are free of most soil pests. They are fed with nutrient solution, usually at every watering or nearly so, at a pH of about 5.5-6.5. Most "potting soil" sold in bags is actually a soilless peat or coco mix with lime and a starter charge of fertiliser that runs out in a few weeks.
Air-filled porosity, how much of the pot is air after drainage, matters more than which material is used.
Don't confuse with
- Hydroponics: often overlaps; soilless media fed with mineral solution are frequently called hydro.
- Soil: contains mineral particles and, in living soil, a managed microbial population.
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.Rockwool is an inert growing medium spun from melted basalt rock into fibres, sold as plugs, cubes and slabs, that holds water and air in fixed proportions.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.Clay pebbles (LECA) are fired, expanded clay balls used as an inert hydroponic medium that drains freely, holds a little water and anchors roots.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.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.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.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.Hydroponics is growing plants without soil, feeding roots a complete mineral nutrient solution either directly in water or through an inert medium.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.A growing medium (plural media) is the material roots grow in, such as soil, coco, rockwool or clay pebbles, which anchors the plant and holds water, air and sometimes nutrients.
