Substrates & Growing Systems

Definitions for growing media and the irrigation systems built around them — what a substrate or setup is and where it is typically used, not which one to choose.

aeration

The presence of air pockets within a growing medium, alongside water and solid particles. Roots need oxygen from these pockets to respire, so a medium that stays waterlogged and excludes air can suffocate roots even while it holds plenty of moisture. Coarse materials like perlite are often mixed in to keep pockets open.

aeroponics

A growing method where roots hang in an enclosed chamber and are misted with nutrient solution at intervals, rather than sitting in a substrate or standing water. Roots are exposed to open air between mistings, giving them constant access to oxygen. The chamber must stay dark to prevent algae growth on the wet root surfaces.

aquaponics

A system combining fish farming with hydroponic plant growing, where water from the fish tank — containing fish waste — is circulated to the plants. Beneficial bacteria in the system convert the waste into forms plants can absorb as nutrients, and the plants help filter the water before it returns to the fish.

clay pebbles / hydroton

Small, round balls of expanded clay, fired at high heat until they become lightweight and porous. Used as a growing medium in hydroponic systems, they hold little water themselves but drain fast and leave large air gaps between pebbles, and they are reusable after rinsing since they do not break down over time.

coco coir

A growing medium made from the fibrous husk of coconuts, processed and washed into chunks, chips, or fine fiber. It holds water well while still draining excess, sitting between soil and pure hydroponic media in behavior, and it naturally binds calcium and magnesium, which is why cal-mag supplementation is common alongside it.

deep water culture (DWC)

A hydroponic method where roots hang directly in an oxygenated nutrient solution, held in a reservoir below a net pot, with no substrate around the root mass. An air pump and air stone keep the solution oxygenated continuously, since roots sitting in stagnant water would otherwise suffocate.

drip irrigation

A watering method that delivers water or nutrient solution slowly and directly to the base of each plant through small emitters, rather than flooding the whole growing area. Because each emitter can be adjusted, it allows different amounts of water to reach different plants in the same system, and it is common in coco coir and soil setups run on a timer.

ebb and flow / flood and drain

A hydroponic setup where a tray holding pots on a solid substrate is periodically flooded with nutrient solution from a reservoir below, then drained back down after a set time. Plants are fed during the flood cycle and get an air-exposure period during the drain, which is how roots avoid staying constantly waterlogged.

fabric pot / smart pot

A container made of breathable woven fabric instead of solid plastic. Air passes through the fabric walls, which air-prunes roots as they reach the edge — the root tip dries slightly and stops growing outward instead of circling the pot — encouraging a denser, more branched root system inside.

grow bag

A flexible bag, usually plastic or fabric, filled with a growing medium such as coco coir or soil and used in place of a rigid pot. Grow bags are inexpensive, stack flat for storage before use, and their soft sides allow some of the same air-exposure benefit at the edges as fabric pots, though the effect is less pronounced.

humus

The dark, stable organic material left after plant and animal matter has fully decomposed in soil. Unlike fresh organic matter, humus breaks down very slowly, so it persists in soil for years, improving its ability to retain water and nutrients and giving soil its characteristic dark color and crumbly texture.

hydroponic

Growing plants with roots in a nutrient solution or an inert medium rather than soil, with all nutrition supplied through the water rather than drawn from organic matter in the ground. Because there is no soil buffering pH or nutrient levels, a hydroponic grower has direct, immediate control over — and responsibility for — everything roots receive.

Kratky method

A passive hydroponic technique where plant roots sit in a sealed reservoir of nutrient solution with no pump or aeration at all. As the plant absorbs water, an air gap opens above the solution, exposing part of the root mass to oxygen, so the system self-adjusts without any moving parts or electricity.

living soil / super soil

A soil mix built with a diverse population of microbes, fungi, and organic amendments intended to remain biologically active for the whole growing cycle and beyond. Nutrients are supplied mainly through microbial breakdown of organic matter already in the mix rather than by regular liquid feeding, which is what distinguishes it from an ordinary potting soil dosed with fertilizer.

loam

A soil type made of a balanced mix of sand, silt, and clay particles, in proportions that avoid the drawbacks of any single particle size. It drains better than clay-heavy soil while holding more water and nutrients than sandy soil, which is why it is often described as a general-purpose soil texture for plant growth.

nutrient film technique (NFT)

A hydroponic system where a thin, continuously flowing film of nutrient solution runs along the bottom of a sloped channel, over bare roots resting in it, then drains back to a reservoir. Because the film is shallow, most of each root stays exposed to air above the flowing solution, combining constant feeding with constant oxygen access.

perlite

A volcanic glass heated until it expands into lightweight, porous white granules. Mixed into soil or coco coir, it creates air pockets and improves drainage without decomposing over time, since it is an inert mineral rather than an organic material. It holds a small amount of water on its porous surface while letting excess drain freely.

recirculating deep water culture (RDWC)

A deep water culture setup where multiple buckets, each holding a plant's roots in solution, are connected by tubing to a shared reservoir, and a pump circulates solution between all of them. This keeps nutrient concentration, pH, and temperature consistent across every plant, unlike standalone DWC buckets that can each drift differently.

rockwool

A growing medium made by melting volcanic rock and spinning it into fine fibers, pressed into cubes, slabs, or blocks. It is sterile and holds both water and air well within its fiber structure, making it a common medium for starting cuttings or seedlings and for full hydroponic setups, though it does not break down and must be disposed of after use.

run-to-waste

An irrigation approach where nutrient solution passes through the growing medium once and the runoff draining out the bottom is discarded rather than collected and reused. Because used solution is never recirculated, there is no buildup of imbalanced salts over multiple cycles, at the cost of using more water and nutrients overall.

soil amendment

Any material mixed into soil to change its physical or biological properties, rather than to supply nutrients directly the way a fertilizer does. Perlite improves drainage, compost adds organic matter and microbial life, and lime shifts pH — each amendment addresses a different soil characteristic rather than feeding the plant on its own.

substrate / growing medium

The general term for whatever material a plant's roots grow into — soil, coco coir, rockwool, clay pebbles, or any other option. It provides physical support for the plant and, depending on the material, plays a role in holding water, air, and nutrients available to the roots. See substrates.

vermiculite

A mineral that expands into lightweight, layered flakes when heated, used as a soil additive. Unlike perlite, vermiculite holds a large amount of water between its layers and releases it slowly, so it is used where moisture retention matters more than drainage, such as in seed-starting mixes.

vertical farming

Growing crops in stacked layers rather than a single horizontal plane, typically indoors under artificial light with hydroponic or similar soilless systems. Stacking multiplies the growing area achievable within a given floor space, though each layer needs its own light source since natural sunlight cannot reach lower levels.

wicking system

A passive watering setup where a wick material draws water upward from a reservoir below into the growing medium through capillary action, similar to how a candle wick draws wax. Plants pull moisture as needed without a pump, which makes the system self-regulating but limits it to smaller containers where the wick can reach evenly.