Basic additives

Vermiculite

This used in composts to help lighten compost mixes and increase its water retention. It can also be used on its own for the propagation of cuttings.

It looks and feels like gold metallic polystyrene and is made from an expanded mica and is very lightweight. Vermiculite can be purchased in bags from most Garden Centres.

Perlite

Made from expanded volcanic rock granules Perlite is used in compost mixes to increase its water retention and to improve aeration of the soil.

It looks like crushed polystyrene and is white in colour. Perlite can be purchased in bags from most Garden Centres.

Horticultural Grit

Available in various sizes (grades) Horticultural Grit is used to improve drainage and aeration. Often used for alpines, and in herb beds.

It looks like small gravel and can be purchased from most Garden Centres.

Horticultural Sand

Used to make compost lighter and more open in texture. Is often combined with grit to create light free draining compost.

Pale coloured sand available in small bags from most Garden Centres.

John Innes 1,2 and 3

John Innes is blended compost to three different ‘recipes’ tailored for three different growing purposes.

• John Innes No1 is low in fertilizer and sow is most suitable for using with seedlings and with plants that do not have high nutrient needs.
• John Innes No2 has twice the amount of fertilizer and limestone as No1 and is suitable for the general growing of plants.
• John Innes No3 contains three times the amount of fertilizer and limestone as No1 and is used for the growing of nutrient hungry plants as well as trees and shrubs.

None of the above is suitable for acid loving plants due to the content of limestone in the mix. A specialist Ericaceous compost is needed for such plants.

Written by Day Lily on 2006/12/20 | Permalink to this article