The formulation of composts for the establishment and growing on of young plants follows on from seed composts in much the same pattern. It is necessary to prepare a compost that allows the development of a root system; contains adequate water to support the plants and sufficient nutrients not to check growth; has a suitable acidity/ alkalinity status; and does not dry out too easily.
Nowadays such composts are based on the use of peat, although traditionally the John Innes concepts were based on the use of sterilized loam. The recommendation of loam as a base for composts has had to be discontinued because it is no longer feasible to obtain a standard material on which a recipe can be formulated. Peat is capable of being relatively standardized and so currently forms the basis. It is important, however, to realize that loam has a steadying and controlling influence on both water and nutrient availability that peat does not provide, and so peat-based (that is, loamless) composts require a higher degree of management and maintenance. Therefore it is prudent to use loam as a minor component merely to provide the buffering action and so ease management. In practice the aim is to produce a loamless compost with added loam!
Young plants also need nutrient in the compost and this should be added at the rate of 4oz fertilizer base per bushel of compost unless the manufacturer recommends otherwise.
There are, of course, many available proprietary brands of peat-based composts, all of which have been tried and tested successfully. Their main disadvantage is their capacity for drying out and the difficulty of rewetting a dried compost, although this latter factor is less of a problem if a wetting agent has been incorporated. Their chief advantage is that they are ready mixed and come packed in handy-sized plastic bags.
If a peat-based compost proves difficult to rewet, then add a small quantity of wetting agent or spreader such as soft soap. Do not use washing-up liquids.
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