Compost bases for soilless composts were introduced by Garden Direct in 1967 to amateur gardeners after many years of intensive trials. The basic principle is that peat is used to make the compost, being the ideal structure to promote root growth, but is almost void of nutrients and trace elements and is strongly acidic. A compost base, therefore, contains plant foods, trace elements and is strongly acidic. A compost base, therefore, contains plant foods, trace elements and neutralising agent to bring the peat to the correct pH. 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 and sand or grit, vermiculite or perlite to improve drainage. When using Garden Direct Bases it is not usually necessary to add other nutrients, unless a very acid peat is used. There are now wetting agents and moisture retaining agents available which affect the structure and form of the compost.