The use of some sort of material to be spread on the ground to a certain height, which acts as an insulating layer between the soil's surface and the atmosphere, or mulching in short, is a technique being increasingly employed by professional horticulturalists. Some home gardeners may still be insufficiently aware of its importance, so in this article I'll tell you why a mulch layer is so important, then I'll go into the different types of mulch, their various qualities and how they should be used.

Amongst many benefits, a mulch on the soil -

* Significantly reduces weeds. This is true of annuals although mulching does not generally prevent the growth of perennial weeds
* Significantly reduces the evaporation of moisture from the soil surface and is therefore an essential part of water conserving gardening
* Reduces soil erosion caused by wind and rain. This is a fantastically important benefit
* Moderates the top-soil temperature. So in the winter a layer of mulch can prevent freezing, and in hot- summer climates, prevent the top soil reaching temperatures that inhibit plant growth
* Is aesthetically superior to the sight of bare soil and irrigation pipes

Taking aesthetic considerations into account, there are broadly speaking two types of mulch which are viable in a garden. Organic mulches such as wood chippings, and natural inorganic mulches such as pebbles. Which is preferable?

The use of decorative pebbles is often part of an overall design. They are particularly appropriate, associatively, in dry climate gardens. But there are a number of drawbacks involved. Some aggregates such as dark stones of volcanic origin have been found to actually increase the top-soil temperature. Furthermore, adding organic feeds to the soil, something that should be done once or twice a year, becomes difficult and tiresome. The use of a chemical fertilizer pump offers a way round this, but sets in train a number of problems. Relying on chemical fertilizers as the only method of feeding is dreadful gardening! For further discussion on the automatic fertilizer pumps, see a previous article of mine called "The truth about fertilizer pumps."

On the other hand, while wood chippings may in some cases be less attractive, they help to create a better habitat in which your garden plants grow. Organic mulches definitely moderate the soil's temperature, they provide raw material for essential organisms like earthworms, (see article called "The world's greatest gardener!") and as they break down they contribute humus to the soil. All these factors reduce pest and disease infestations, improve the soil's structure, and in the long run help to provide balanced nutriment for the plants

For organic mulches to be effective, they need to be spread to a depth of about 10 cm, after the initial quantity has settled. This means you need to spread about 15cm in order to end up with a layer of some 10 cm, and you'll need to add a bit each year as the chippings closest to the soil's surface break down. Be careful to keep the mulch away from tree trunks and shrub stems. It could cause rot to set in.