Perlite is volcanic glass heated rapidly until trapped water flashes to steam and the grains pop like popcorn into light, porous white granules. In a mix it creates large pores that drain quickly and fill with air, raising the air-filled porosity of the medium. It is essentially inert, near neutral pH, and supplies no nutrients.
In practice
Common blends are 10-30% perlite in soil or peat mixes and 20-40% in coco. More perlite means faster drainage and more frequent watering. It floats to the surface over time and can be blown about when dry; wet it before mixing and wear a dust mask, since the fine dust is an irritant. It does not break down, so it can be reused after cleaning.
Pumice does a similar job, is heavier and does not float.
Don't confuse with
- Vermiculite: also expanded mineral, but it holds water and nutrients; the opposite job.
- Clay pebbles: larger aggregate used as a hydro medium on its own.
Popcorn buds are small, separate buds, usually from lower branches, often sold cheaper as "smalls" though they can be the same quality as the tops.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.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.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.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.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.Vermiculite is expanded mica-like mineral flakes that hold water and nutrients in a mix, used to increase moisture retention rather than drainage.Clay pebbles (LECA) are fired, expanded clay balls used as an inert hydroponic medium that drains freely, holds a little water and anchors roots.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.Overwatering is watering so often that the medium stays saturated, starving roots of oxygen, which causes drooping, slow growth and root disease.
