British Cactus and Succulent Society

Highlands & Islands Branch

Plant Management


John Innes Composts


John Innes was a very successful nineteenth century property and land dealer and was one of the founders of the City of London Real Property Company. On his death in 1904 he bequeathed his estate to be used for the promotion of horticultural instruction, experimentation and research. The result was the establishment, in 1910, of the John Innes Horticultural Institution, on 5 acres of farmland adjoining Merton Park, Surrey.

Before John Innes composts were introduced, gardeners and commercial horticulturists relied on 'good' garden soil, or used composts produced to their own recipe, for potting seeds and plants. It was common to find a different compost formulation being used for each plant species being grown. These composts and soils were not usually sterilised and so seedlings were often damaged or destroyed by soil-borne pests and diseases. These composts and soils were of variable quality as were the fertilizers added to them to promote plant growth. The consequent nutritional imbalances led to plants being either too "soft" and therefore liable to disease, or very "hard" and slow growing.

In the 1930's William Lawrence and John Newell, two scientists at the John Innes Horticultural Institute, set out to formulate composts that would give consistently good and reliable results. Their particular motivation was the difficulty they were having in growing Chinese Primrose (Primula sinensis) for experimental purposes. Their objective was to obtain much better and more reliable germination and growth among their experimental materials by standardizing growing conditions, including the growing medium. Through experimentation they established methods of heat sterilising the compost to destroy pests and diseases that did not cause any checks to plant growth. They also determined the physical and nutrition qualities needed in compost to achieve optimum plant growth. Lawrence and Newell also took into account the need to alter the nutritional status of the compost according to the plant's growth stage. Their research led to the introduction of the two standard composts, one for seed sowing and one for potting, which revolutionised the growing of pot plants.

(Extracted from the web-site of the JI Centre January 2007)

The base compost is, in parts by volume

  1. good quality sterilised loam = 7

  2. sphagnum moss (or peat)   = 3

  3. sand = 1

To each cubic metre is added:
  1. 594g of limestone or
    1.2Kg of hoof & horn
  2. 1.2Kg of superphosphate of lime
  3. 594g of potassium sulphate
All this is based on the original formula which was
  1. 1lb of ground limestone
  2. 1lb of potassium sulphate
  3. 2lb of hoof & horn
  4. 2lb of superphosphate of lime
   per cubic yard.

It is said that the original formula was JI-1 and that JI-2 has twice as much fertiliser, and that JI-3 has three times as much.

JI Seed Compost
  1. 2 parts (by volume) of sterilised loam
  2. 1 part of peat
  3. 1 part of sand
To each cubic metre is added -
  1. 1.2Kg (2lb) of superphosphate of lime
  2. 594g (1lb) of ground limestone
The whole mixture has to be quite fine so that seed can make good contact.
Cutting Compost

First requirement is that it be free-draining and able to function in high humidity without causing damping-off. It may be suitable for some succulents, but not cacti, These composts typically comprise -

  1. 50% of sand
  2. 50% of peat
    To each cubic metre is added

    1. 4.4Kg of dolomitic lime
    2. 1.5Kg of hoof & horn or dried blood,
      superphosphate of lime, calcium carbonate
    3. 148g (4oz) each of potassium nitrate
      and of potassium sulphate.

      They say that because cutting composts are low in nutrients, cuttings need to be fed once rooted.

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