Mulching has deserved popularity

Press, 17 September 1976, Page 10

Mulching has deserved popularity

Mulching in all its many forms is widely practised today although not everybody will have the same reasons for following it. The main reason for forming a mulch as a ground cover is to minimise the labour involved in keeping it clean. As a weed suppressant a good mulch can be most effective and what unwanted growth does emerge is

easily pulled out or can be dealt with by spot spraying, a particular help in dealing with tenacious perennial weeds. . A mulch will also help to conserve moisture by checking evaporation, and in this respect it is very useful in exposed places and areas subject to drying oui. It can assist in stabilising soil temperature so that warmth is retained for much longer in winter while the soil may remain cooler in the hottest time of the year.

Mulching can also influence soil texture, improving tilth and hence friability, particularly in heavy soils which thus become more manageable. This improvement to the soil results in better root systems by the plants which in turn enhances their growth. And as organic mulches break down in time they provide an additional source of food for the soil, also it can help to stimulate a greater earthworm population.

Mention of organic mulches brings to notice that there are two forms of mulch which can be applied; Organic materials which can be and are used include sawdust, bark chip, pine needles, shoddy, grass clippings, straw, leaf mould, seaweed and various combinations of litter. The second form of mulch comprises inorganics such as polythene, shingle and flat stones. The use of inorganics is predominantly dual purpose, to enhance appearance and to suppress weeds ,but can also

be of economic importance when used in cropping.

The choice of materials is usually an individual one and perhaps requires little or no elaboration with the exception of one point and that concerns the use of polythene. Polythene is often used as the base over which other material is placed. Large areas should not be underlaid in this way where drainage is poor or the soil is heavy as this can make conditions untenable for plants to grow in. Although poor drainage is always restrictive to most plants other inorganic (apart from polythene) and organic materials can be used. Sawdust must be completely free of preservatives, and is preferably only to be used after it has been weathered for some time. If applied in a fresh state it can temporarily deplete the soil of nitrogen which is used in its own breakdown pro-

cess and as a consequence plants may suffer.

The addition of ammonium sulphate at 115 g per square metre per scm depth of sawdust is recommended. Double this quantity should be used if blood and bone is applied, but only half this amount if urea is used. Animal manure type mulches can cause immediate trouble if raw, the release of ammonia being strong enough to kill tender plants and severely scorch others.

Grass clippings should be lightly scattered preferably after being allowed to wilt and should not be banked up against the base of trees and shrubs.

Take care not to apply mushroom compost in the vicinity of any acid loving plants such as rhododendrons, azaleas and ericas and do not over-use it generally as the high alkalinity of much of this composition will not be excessively tolerated by many other trees and shrubs, young ones in particular.