Monday, January 21, 2013


Mulching not only helps to reduce evaporation, but conserves soil moisture, reduces watering and provides a cooler root-run for the plants, as well as reducing the number of weeds consuming precious water. Water absorbing mulches such as paper, straw or uncomposted lawn clippings can be a problem in a hot dry climate. A mulch of Pinus radiata chips, stained to resemble red gum, has the advantage of not absorbing water.

Mulching also allows a change of watering pattern that can greatly benefit some plants. An example we see is a box hedge, previously dying from the use of bore water. Now mulched, it is recovering well. Mulch material that has not been composted can cause short term nitrogen loss from the soil beneath. As bacterial microbes use available nitrogen to aid in decomposition of the mulch above, nitrogen in the soil is depleted. Composted pinebark mulch does not have this problem. The yellowed leaves of herbaceous plants, caused by nitrogen or a nitrogen deficiency, can be relieved by the use of liquid feed containing nitrogen.

Another good composted mulch is made from wood-fibre waste from the paper-making industry. It can also be made from such things as wood crates or council collected green organic materials. It compacts well, doesn't blow away although it can have an organic odour for a few weeks. When using mulches, or composts, make sure it is kept away from the stems of plants as this can lead to fungal decay. Contrasting colours of mulch can look effective, such as composted wood-fibre spread around plants beside a path of red gum chips, although over time the contrast fades.

Organic mulches have the added benefit of adding life to the soil but can generate humidity. Non organic mulches, like aggregate, are sometimes more suitable, and probably involve less labour. Australian plants, especially dryland species in particular benefit from a reduction in the humidity generated by organic mulches. An aggregate resembling river pebbles, but a by-product of sand mining, is shown around a pool-side box hedge. Any inert aggregate material can be used for mulching. Coloured bricks or broken glass are currently a popular choice, as are river pebbles, but these are now difficult to source. Scoria and marble chips can look dramatic but are quite expensive. Gravel and crushed rock are the cheapest aggregates, however prices and colours can vary.

No comments: