WHAT IS JOHN INNES COMPOST?

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, trained gardeners generally used a different compost recipe for each species of plant they wanted to take cuttings from or pot up. And of course, these recipes were guarded close to the chest.

Be that as it may, it was quite usual for the soil to be either 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 was usually ‘unbalanced’, causing the plants to be either too soft in their growth and therefore more 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.

William Lawrence and John Newell developed a blend of carefully selected loam or topsoil, sphagnum moss peat, coarse sand or grit and additional 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. These ratio of these ingredients depended on which mix was being created

Now, after being used very widely for over 50 years, the basic formulae remain the same - tried and tested and still popular amongst gardeners for growing quality plants with the minimum of attention. Naturally, in today’s compost mixes the plant nutrients have been updated to gain the benefits of improved fertilizer technology.

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