A growing medium, or substrate, is whatever the roots grow in. It anchors the plant and holds a balance of water and air; some media (soil, compost, peat, coco) also hold and supply nutrients, while others (rockwool, perlite, clay pebbles) are nearly inert. "Media" is the plural.
In practice
Media are judged by a few properties: water-holding capacity, air-filled porosity, cation exchange capacity, pH, salt content (starting EC), stability over time and cleanliness. These decide how often to water, how to feed, and how forgiving the system is. Soil and amended mixes buffer mistakes; inert media give fast, precise control but punish errors quickly.
Choosing a medium is the first and most important systems decision: see choosing a system.
Don't confuse with
- Root zone: the environment around the roots, including solution and microbes.
- Medium (DWC): in water culture the "medium" in the net pot only anchors the plant; roots live in solution.
Clay pebbles (LECA) are fired, expanded clay balls used as an inert hydroponic medium that drains freely, holds a little water and anchors roots.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.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.EC (electrical conductivity) measures how well a solution conducts electricity, a proxy for total dissolved salts; growers read it in mS/cm to gauge nutrient strength.The root zone is the volume of medium or solution where a plant's roots live, including its water, air, temperature, pH, EC and microbes.DWC (deep water culture) suspends a plant's roots in an aerated nutrient solution, typically in a bucket with a net pot lid and an air stone.A net pot is a plastic cup with slotted or mesh walls that holds a plant and its medium in a hydroponic lid, letting roots grow through into solution.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.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.A soilless medium contains no mineral soil, such as peat, coco, rockwool or perlite blends, and relies mostly on the grower to supply nutrients.
