John Innes Compost
Soil-based seed and potting composts formulae containing loam, sand, peat, (or peat substitute), ground chalk, and varying amounts of added fertilisers, according to their purpose. The formulae was developed by the John Innes Horticultural Institute in the 1930s. J I Seed Compost contains some added superphosphate; J I Nos 1-3 contain the ‘JI base mix’ of fertilisers (i.e. hoof and horn meal, superphosphate and potassium sulphate), in increasing quantities. J I No 1 contains the least base mix (suitable for temporary bedding plants), J I No 2 contains more base mix (for pot plants preferring poorer soils), and J I No 3 contains the most base mix (for vigorous pot plants with heavy feeding requirements, and for long-term pot plants). There are also ericaceous versions for acid-loving plants. As loam is currently in short supply, not all brands actually follow the original formulae.