Expanded clay aggregate
- Suitable for hydroponic systems in which all nutrients are carefully controlled in water solution.
- re-usable because they can be cleaned and sterilized, typically by washing in:
- solutions of white vinegar
- chlorine bleach
- hydrogen peroxide
- and rinsing completely.
- but: best not re-used even when they are cleaned, due to root growth that may enter the medium.
- Made from glass waste
- more air and water retention space than perlite and peat
- holds more water than parboiled rice hulls.
- also known as coir or coco
- colonized with trichoderma fungi, which protects roots and stimulates root growth
- extremely difficult to over-water
- high cation exchange, meaning it can store unused minerals to be released to the plant as and when it requires it.
- Coir is available in many forms
- volcanic rock that has been superheated
- used loose or in plastic sleeves immersed in the water.
- similar properties and uses to vermiculite but, in general, holds more air and less water and is buoyant.
- mineral that has been superheated until it has expanded into light pebbles
- natural “wicking” property that can draw water and nutrients in a passive hydroponic system.
- If too much water and not enough air surrounds the plants roots, it is possible to gradually lower the medium’s water-retention capability by mixing in increasing quantities of perlite.
- does not hold water very well
- must be sterilized between uses
- same type that is used in aquariums
- any small gravel can be used, provided it is washed first.
- easy to keep clean, drains well and will not become waterlogged
- if the system does not provide continuous water, the plant roots may dry out.
- produced from steam friction of wood
- keeps its structure for a very long time
- wood fibre may have detrimental effects on “plant growth regulators”.
- little-used yet promising
- greatest yield out of the tested substrates
- most widely used medium in hydroponics.
- typically used only for the seedling stage, or with newly cut clones
- can remain with the plant base for its lifetime
- can be engineered to hold large quantities of water and air
- good mechanical structure to hold the plant stable
- possible skin irritancy (mechanical) whilst handling (1:1000)
- naturally high pH of mineral wool makes them initially unsuitable to plant growth and requires “conditioning” to produce a wool with an appropriate, stable pH.
- similar properties to gravel.
- possibly altering the pH
- requiring extra cleaning before reuse.
Polystyrene packing peanuts
- readily available
- excellent drainage
- used mainly in closed-tube systems
- non-biodegradable polystyrene peanuts must be used
- too lightweight for some uses
- biodegradable packing peanuts will decompose into a sludge
- Plants may absorb styrene and pass it to their consumers