Special Soil Mixtures
Pick up any British gardening publication of the past two decades and chances are you will see something about John Innes Composts. Developed between 1934 and 1939 at the John Innes Horticultural Institution, these special mixtures of soil ingredients have been pretty well standardized as growing mediums for seedlings and pot plants. So sacred are they to gardeners in England (where the mix­tures are sold pre-packaged) that I suspect my comments about them will earn me a disapproving look or two. In spite of the public adulation given these mixtures, I believe the specialists who devel­oped them will agree with me that they were never intended to be the ultimate, perfect blends for growing a wide range of plants.

Reading between the lines, my guess is that what the scientists were really striving for were standardized, uniform growing me­diums that would always respond in the same way. These were de­signed for scientific research, so the factor of soil could be consid­ered an invariable in all tests. As can be appreciated, when a scientist tries to check differences in the qualities, functions or responses of plants, one thing he must have is a uniform environment.

John Innes Composts are nothing more nor less than standard soils for research work and should be considered in that light. That they work out well as seed growing and potting mediums is a happy by-product, which has led to a much wider use than I am sure was intended at first.

Here are the formulae for two of these special composts:


3/4 parts (by volume) coarse sand;
31/2 parts (by volume) peat, and
7 parts (by volume) composted medium loam.

To each cubic yard of the above, add and mix in thoroughly two pounds of superphosphate (18 per cent phosphoric acid) and one pound of chalk (calcium carbonate).


2 parts (by volume) coarse sand;
3 parts (by volume) peat, and
7 parts (by volume) composted medium loam.

To each cubic yard of the above, thoroughly incorporate the following:

Two pounds hoof and horn meal (13 per cent nitrogen); Two pounds superphosphate (18 per cent phosphoric acid); One pound sulfate of potash (48 per cent potassium), and One pound chalk (calcium carbonate).

There are several obvious disadvantages to such mixtures. Me­dium composted loam would not be a uniform product by any means. Workers at John Innes might use loam from the same field each time, but chances of others matching this in other locations would be rather remote. Coarse sand in one man's language might be something approaching gravel in another's.

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