The John Innes seed compost contains 2 parts loam, 1 part peat and 1 part coarse sand (parts by volume) together with 43 grams (1 ½ ounce) superphosphate and 21 grams (¾ ounce) chalk per bushel of the mixture.
John Innes Compost No. 1
John Innes Potting compost No. 1 consists of 7 parts loam, 3 parts peat and 2 parts sand, plus 112 grams (4 ounces) base fertilizer and 21 grams (¾ ounce) chalk per bushel. The base fertiliser is made up of two parts hoof and horn (13% N), 2 parts superphosphate (18% P2 O5 ) and 1 part sulphate of potash (48% K2O) (parts by weight); this can also be bought ready made-up and added if you are making your own compost.
John Innes Potting compost No. 2 and 3
John Innes Potting Compost No.2 and No.3 contain twice as much and three times as much, respectively, of chalk and fertilizer.
John Innes No.2 is used for plants in 12.5 – 20.5cm (5-8in) pots; John Innes No.3 is for anything larger.