Up until the beginning of the 20th century there were no ‘standard’ compost mixes for plants. In fact, before the introduction of John Innes Composts gardeners generally used a different compost for each species of plant they wanted to take cuttings from or pot up.

Usually the soil was neither sterilised or heat pasteurised and consequently plant seedlings were often attacked and destroyed by soil-borne diseases and insects.

In addition, the plant nutrition that was being added to the traditional composts were usually ‘unbalanced’, causing the plants to be either too soft in their growth and liable to diseases, or overly tough and slow growing.

In the 1930's two research workers at the John Innes Horticultural Institute, William Lawrence and John Newell, set out to overcome these problems by formulating composts that would give consistently good and reliable results. After six years of experiments they determined the physical properties and nutrition necessary in composts to achieve optimum rates of plant growth. They also introduced methods of heat sterilising the soil that eliminated pests and diseases, but did not cause any retardation of plant growth.

The result of this work was the introduction of two standard composts, one for seed sowing and one for potting. These "John Innes" composts revolutionised not only the ways in which composts were produced, but also the growing of plants in pots. Now, after being used very widely for over 50 years, the basic formulae remain the same - tried and tested and still popular amongst discerning gardeners for growing the best quality plants with the minimum of attention. Naturally, the plant nutrients have been updated to gain the benefits of improved fertiliser technology.

John Innes Composts are a blend of carefully selected loam or topsoil, sphagnum moss peat, coarse sand or grit and fertilisers. The loam is screened and sterilised and then thoroughly mixed with the other ingredients in proportions designed to achieve the optimum air and water-holding capacity and nutrient content for different types and sizes of plants.

John Innes Base Fertiliser is the name coined at the John Innes Research Institute in the 1930's for a ready mixed blend of hoof and horn, superphosphate and potassium sulphate for mixing with loam, peat and grit to make John Innes Loam-based Potting Composts.

The following lists gives the formulae for the Composts - the proportions of the substrate are measured by volume, with loam and peat passed through a 9mm sieve. For the No. 1,2 and 3 composts the John Innes base fertilizer consists of 2 parts Hoof and Horn for the Nitrogen (N), 2 parts Superphosphate for roots (P)and 1 part Potassium Sulphate (K) for flowers and fruit. This is balanced with one part ground limestone (CaCO3) to provide an optimum pH.

For growing seeds, cuttings and ericaceous or calcifuge plants (plants which require acidic conditions) the proportions vary and for the latter the ground limestone is replaced with an equal quantity of Flowers of Sulphur which lowers the pH.

Compost Substrate Fertilizer rates for the John Innes base are per each cubic metre of mixed compost.

John Innes No. 1

7 parts loam
3 parts peat

2 parts sand 0.6kg ground limestone

1.2kg hoof and horn,1.2kg superphosphate
600g Potassium Sulphate

John Innes No. 2

7 parts loam
3 parts peat

2 parts sand 0.6kg ground limestone

2.4kg hoof and horn
2.4kg superphosphate
1.2kg Potassium Sulphate

John Innes No. 3

7 parts loam
3 parts peat

2 parts sand 0.6kg ground limestone

3.6kg hoof and horn
3.6kg superphosphate
1.8g Potassium Sulphate

John Innes Seed Compost

2 parts loam
1 parts peat

1 part sand 600g ground limestone

1.2kg Superphosphate

John Innes Cutting Compost

1 parts loam
2 part peat

1 part sand no added fertilizer

John Innes Ericaceous Compost

2 parts loam
1 part peat

1 part sand 600g Flowers of Sulphur

1 part superphosphate

Mixing is more easily performed if the ingredients are not too moist so that the particles do not stick together and so become more evenly distributed. Storage should be kept to a minimum as the nutrient balance will change due to the Nitrogen being mineralised by bacteria to unavailable Nitrate (NO3=) ions.

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