THE USE OF VARIOUS COMPOSTS AND RECYCLED MATERIALS IN GROWING MEDIA FOR ORNAMENTAL SHRUBS

The proportion of compost that can be used is limited by high nutrient content, high contents of soluble salts, calcium carbonate, sodium and chloride. Composts containing high proportions of wood may immobilize nitrogen. Poor substrate structure or low structural stability may also be disadvantageous. If properties of composts are to be improved by addition of recycled materials, these materials must contain low quantities of nutrients and of soluble salts and be of stable structure.

In trials to study such developments Deutzia scabra was cultivated in growing media made from mixtures of various composts and peat. The growth of these plants was just as good as in peat substrates, in peat substrate mixtures containing either: up to 20% of bio-waste compost (BWC), compost of anaerobically treated refuse (CAR) from dry fermentation, 40% garden waste compost (GWC) or 60% CAR from wet fermentation.

Recycled materials of low nutrients status were added to a substrate containing 25% GWC in order to reduce the proportion of peat to 50% or 25% of the substrate. In substrates with the addition of 25% crushed brick, and/or 25% composted bark and/or 25% or 50% wood chips the growth of Potentilla fruticosa was just as good as in a mixture of 75% peat and 25% GWC.

In the cultivation of ornamental shrubs very useful substrates can be produced containing only 25% or 40% of peat if suitable composts and other recycled organic or mineral materials are being used.

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