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13 January 2014

What Are John Innes Composts?

Amongst the wide range of composts at your local garden centre you may have seen bags of John Innes composts and wondered what they were and why they cost more than the others. This article should give you some basic information.

John Innes was a nineteenth century property and land dealer in the City of London who died in 1904, and bequeathed his fortune and estate to the improvement of horticulture by experiments and research. This led to the establishment of the John Innes Horticultural Research Institute, which is now based in Norwich.

In the 1930's two research workers at the John Innes Horticultural Institute, set out to formulate composts that would give consistently good and reliable results. After six years of experiments they identified the physical properties and nutrition necessary in composts to give the best rates of plant growth. They also introduced methods of heat sterilising the soil that eliminated pests and diseases, but did not cause any checks to plant growth.

This work resulted in the introduction of two standard composts, one for seed sowing and one for potting. After all these years the basic formulae remain the same, although the plant nutrients have been updated to make use of improvements in fertiliser technology.

There are five blends of John Innes compost, each designed for a particular task.

JOHN INNES SEED COMPOST - the traditional compost for sowing almost any type of seed, with enough nutrients for early development. It can also be used for rooting soft cuttings.

JOHN INNES POTTING COMPOST No.1 - for potting-up and pricking-out young seedlings or rooted cuttings. It's carefully balanced nutrient content suits most young plants.

JOHN INNES POTTING COMPOST No.2 - for potting-up most house plants and vegetable plants into medium size pots or boxes. This compost has double the amount of nutrients found in John Innes No 1 as required by established plants.

JOHN INNES POTTING COMPOST No.3 - a richer mixture suitable for final re-potting of heavy-feeding vegetable plants, and for mature shrubs and foliage plants in interior planters or outdoor containers.

JOHN INNES ERICACEOUS COMPOST - A specially formulated lime-free version with the necessary nutrients for most lime-hating plants, such as Heathers, Rhododendrons and Azaleas etc.

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

Loam is the main ingredient in the compost as it provides the main "body". It also forms the base of plant nutrition by supplying clay, which absorbs and releases plant nutrients as required. Loam also contains some essential micro-elements and organic matter which slowly release nitrogen to the plant.

Sphagnum Moss Peat increases the total porosity and improves the aeration and the water-retaining capacity, before slowly decomposing into humus.

The coarse sand or grit is used to improve the drainage of the compost and thus prevent water-logging. It also helps to provide stability for larger plants.

The compound fertiliser in John Innes Compost provides a wide range of plant nutrients needed for balanced growth, including nitrogen, potash, phosphates and trace elements.

As loam is currently in short supply, not all brands actually follow the original formulae. You can also obtain peat-free John Innes composts where the peat is replaced by green compost. Study the description on the bag to make sure that you know what you are buying.

John Innes composts have clearly stood the test of time, and are still popular with discerning gardeners - why not give them a try?

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