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JOHN INNES COMPOSTS

John Innes, a merchant in the City of London, died in 1904 and a bequest from his estate established the John Innes Horticultural Institute in 1910 at Merton in South London to carry out horticultural research. It has moved a couple of times since and is now situated at Colney, near Norwich.
Some of the earliest work under the first director, William Bateson, was on plant breeding and genetics. To ensure consistent results when carrying out experiments, in the mid 1930's, they developed sterile growing media. These potting composts have never been produced commercially at the Institute, but the formulae were made public and are now used by many manufacturers and growers.
One of the current tasks carried out by the Institute is gene sequencing of plants. This information can be used in the enhanced breeding of plants as resistance to disease and tolerance to environmental conditions carried on certain genes can be selected and these plants used for crossing. This is not genetic modification, but is a more direct way to achieve the desired characteristics in the progeny plants.

There were four different grades of the composts originally, made using loam, peat and sand with varying amounts of nutrients added depending on the use for the final product. All were sterilised with steam to kill any seeds in the loam and remove fungal or other microbial pathogens which could damage the plants.
Some multi-purpose growing composts are described as having "added John Innes". This probably refers to the proportions on nutrients that have been included, as they do not contain loam or sand, and most now have no or a reduced amount of peat.

Seed Compost - has the lowest nutrient content and was formulated for seeds, soft cuttings and pricking out delicate seedlings, all of which can be damaged if the nutrient level is too high. No. 1 - for sowing large seeds and pricking out most other seedlings and rooted cuttings. No. 2 - for potting-on most plants it contains twice the added nutrients of No.1. No. 3 - has the highest nutrient content for potting mature plants and shrubs. Formulae for Cuttings and Ericaceous plants have been added to the range

Loam or good quality topsoil, forms the main part of the substrate and contains clay particles which hold micronutrients. A thin coating of humus on the particles allows ionic exchange to slowly release these nutrients as required by the plant. It should have a pH between 5.8 and 6.5
The original formulae used peat from Sphagnum Moss to increase the porosity allowing air to reach the roots and improves the water-retention. The pH ranges from 3.5 to 5. It can be replaced with a peat-substitute to comply with modern trends to conserve the peat bogs.
The coarse sand improves the drainage, so preventing water-logging, and when used in containers it makes the pot more stable for large plants. It should be lime free.

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The following table gives the formulae for the Composts - the proportions of the substrate are measured by volume, with loam and peat passed through a 9mm seive. 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 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 per cubic metre
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 part peat 1 part sand	600g ground limestone 1.2kg Superphosphate
John Innes Cutting Compost	1 part loam 2 parts 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 become 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.

The use of peat in planting media is frowned upon nowadays because of the environmental damage its extraction causes. It took thousands of years for the peat bogs to be built up and a few minutes to remove it. As long as it remains in the wet conditions, the phenolic compounds present in bogland water preserve the ancient plant tissues almost intact, but removed from this, normal breakdown occurs and the trapped carbon dioxide is released to add to the greenhouse gases already damaging our climate. There is also the loss of habitat for the flora and fauna of peat bogs, where many of them are unique.
Peat is due to be removed from growing media by 2020 and much research has been done to find an alternative, but its unique qualities of moisture retention and release of nutrients have not yet been matched. Most of the growing media available still contain peat to some extent, but the proportion has been reduced. There are some which are completely peat free, but for some tasks such as raising seedlings and cuttings, the results are not as good.
Most of the growing composts now contain green waste which can be variable in quality as it is made from material that could have been treated with herbicides that have not degraded. Recently Which? Gardening magazine reported that the selective weedkiller clopyralid may have been present in some composts and that it caused stunting or distortion of plants grown in them. The organization is also campaigning to have use by dates printed on growing composts due to the loss of nutrients in storage.
When buying bagged growing media it should be stored in dry conditions as the nutrients degrade faster when wet. This can be difficult as most garden centres and DIY stores keep it stacked outside and the bags are sodden.

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