What is Vermiculite and how and why is it used in the garden?
What is Vermiculite?
Vermiculite has been used in various industries for over 80 years. It is used in the construction, agricultural, horticultural, and industrial markets.
Vermiculite is the mineralogical name given to hydrated laminar magnesium-aluminum-ironsilicate which resembles mica in appearance.
Vermiculite is found in various parts of the world. Locations of the predominant commercial mines are in Australia, Brazil, China, Kenya, South Africa, USA and Zimbabwe.
Vermiculite mines are surface operations where ore is separated from other minerals, and then screened or classified into several basic particle sizes.
When subjected to heat vermiculite has the unusual property of exfoliating or expanding into worm-like pieces (the name vermiculite is derived from the Latin 'vermiculare' - to breed worms).
This characteristic of exfoliation, the basis for commercial use of the mineral, is the result of the mechanical separation of the layers by the rapid conversion of contained water to steam.
Uses of Vermiculite
Vermiculite's many uses and beneficial properties include:
¤ Inorganic, and sterile.
¤ No known toxicity or fire hazard.
¤ High water holding capacity.
¤ Non-abrasive and non-irritant.
¤ Absorbs excess nutrients.
¤ Facilitates re-wetting.
¤ Low alkalinity.
¤ High cation-exchange capacity.
¤ Does not deteriorate in storage (if kept dry).
¤ Free from disease, weeds and insects.
¤ Good air holding capacity.
¤ Insulates and minimizes soil temperature fluctuations.
Vermiculite is ideal for the germination of seeds, because it's aeration properties combined with it's water holding capacity make it a very suitable medium for direct contact with the seeds.
When vermiculite is used alone, without compost, seedlings should be fed with a week fertilizer solution when the first true seeds appear. Large seeds can be mixed with Vermiculite in a small polythene bag closed at the neck, and kept in a warm place until the seeds just start to germinate. Then plant them singly in small pots or trays of potting compost. Vermiculite can also be applied to the outdoor seed bed where it will give improved emergence and less risk of capping.
Rootings and Cuttings
Vermiculite/sphagnum moss peat composts stimulate root growth, giving quicker anchorage of the plant and uptake of nutrients.
A 50/50 mix is generally suitable for cuttings on the open bench or under plastic covers, but a maximum of 25% is recommended under mist irrigation in Summer.
Thoroughly water the vermiculite before inserting cuttings, and do not compress around the base of the cutting.
Vermiculite in potting compost gives a very light open compost, holding more water and facilitating re-wetting, thereby lengthening the time between watering. Vermiculite also has excellent ion exchange properties which absorb excess nutrients and release them slowly to the plants via the finest root hairs.
A 50/50 mix of vermiculite and sphagnum moss peat is widely used for greenhouse pot plants and hanging baskets, while a 25/75 mix is generally suitable for for bedding plants, nursery stock, etc.
To improve an existing compost add 20-25% by volume of Vermiculite and mix thoroughly.
See Vermiculite in our Store.