Compost Bases

Compost bases for soilless composts were introduced to amateur gardeners by Garden Direct in 1967 after many years of intensive trials. The basic principle is that while peat is used to make the compost as it has the ideal structure to promote root growth, it is almost void of nutrients and trace elements as well as being strongly acidic. A compost base, therefore, contains plant foods, trace elements and a neutralising agent to bring the peat to the correct pH, creating a multi-purpose compost. It is supplied in a pre-weight form to mix with peat. 
Other additives which are frequently added are bark or leaf mould as substitutes for peat sand or grit as well as vermiculite or perlite to improve drainage. When using Garden Direct Compost Bases it is not usually necessary to add other nutrients, unless a very acid peat is used. Wetting and moisture retaining agents are also available which can improve the structure and form of the compost. 

Peat Wetter
Assures a uniform water distribution, and improves water holding by a third. Aids re-wetting. Eliminates wet and dry spots and reduces the risk of... more info
John Innes Base
This is a more consistent form of J.I. Base, with more reliable slow release ingredients. N.P.K. FERTILIZER 6.4- 9.8- 13.6 Nitrogen (N) 6.4%... more info