Before laying grass as mulch across pathways, ensure that it's dried out first, or it will emit an odour. The actual herbs and vegetable plants in this circular vegetable garden are mulched with dry autumn leaves.

Cape Town - After heavy rain, how can gardeners help in a grand environmental quest to protect the topsoil in their gardens? This winter, make a resolution to cover up all the bare soil in your garden with mulch. Bare soil is a barren, gaping wound in your garden that is prone to erosion.

Start by laying a thick blanket of mulch across your garden beds. Top gardeners spend at least 50 percent of their annual garden budget on compost and mulch, as it is this organic matter that keeps the plants in your garden protected and healthy.

“The quality of food we eat, water we drink, air we breathe and the well-being of all plant and animal life is determined by the quality of our topsoil,” says environmentalist and landscaper Gina Shoemaker. “The earth’s crucial thin layer of soil must be protected, maintained, built and nourished. A thick layer of mulch across the soil enables, conserves and enhances our precious layer of topsoil.”

In healthy woodland, mulch consists of dead leaves, twigs, fallen branches and other plant debris which falls to the forest floor. “Bacteria, fungi and other living organisms use these raw organic materials for food, a process we know as decay. In the natural scheme of things, decay is nature’s way of returning to the earth the raw materials borrowed by previous generations of plants.”

For gardeners, home-made mulch comes in the guise of autumn leaves, which should be packed into a thick layer in garden beds, or superior, commercially-produced mulch, which is available in a wide range of guises from pine bark nuggets to carbon-rich black-composted mulch. “Our winter mulch is a carefully aggregated product that consists of medium to small-sized pine bark compost,” says Earth2Earth’s Donvae Hooker.

“We use pine bark as it has a long residual effect in the soil that enhances and enriches the existing soil structure. The slightly acidic base also stimulates and enhances microbial activity. This process is initiated by earthworms, who reformulate the organic material into a stabilised, long, residual nutrient base within the soil,” she says. “If you are a passionate gardener, choose a mulch that is a certified organic which carries the Bio-Org certification.”

As organic mulch slowly decays over the summer, it not only conserves moisture, but also feeds plants, earthworms, microbes and other beneficial soil life at the surface. Recent scientific experiments carried out in the dry south-west states of the US proves that mulch is very good for your garden.

* It insulates and protects your soil from the hot sun and winds, preventing the soil from drying out or baking hard.

Mulched soils are much cooler than non-mulched soils and have less fluctuation in soil temperature. “Optimum soil temperatures and less moisture evaporation from the soil surface enable plants to grow evenly. Plant roots find a more favourable environment near the soil surface where air content and nutrient levels are conducive to good plant growth,” adds Shoemaker.

* It breaks the impact of falling water from rain or irrigation. Mulch slows down water so that can soak gently into the soil before running off. Mulch also prevents soil from being washed away and mud splashing around. Reducing erosion during the rainy season is an important aspect of managing your garden’s topsoil.

* It reduces reflectivity. Bare sand or clay soil can develop a very bright reflective surface which bounces the heat and light of the sun back on to plants. Mulch provides a darker surface that cuts down on the reflectivity and cools the area around plant stems and leaves; as a result less plant moisture is lost through transpiration.

* It reduces exposure to wind, which results in less moisture loss through evaporation. One study showed that a 5cm layer of leaf litter reduces evaporation by 45 to 65 percent, depending on type of leaf; pine was the best.

* It promotes good root growth by retaining moisture in the root zone.

* It improves the quality and water-holding capacity of soil near the surface as the mulch slowly breaks down.

* It suppresses weed growth by keeping out the light. This is regarded by many horticulturists as a preferable method of weed control to either herbicide or manual removal of weeds.

* It requires no watering, as groundcovers or grass do. All water is therefore available for nearby plants. In dry gardening, it is an excellent companion to trees, as trees will use up water intended for lawn or groundcovers.

* It is regarded as an attractive feature in any landscape.

How much mulch do you need?

Large bark chips should be 10cm to 15cm thick, pine needles 5cm to 7.5cm, bagged commercial mulch 5cm to 10cm, leaves 5cm to 10cm, or peanut shells 5cm to 7.5cm.

How many bags will you need?

For a 10cm deep layer of mulch, one 30dm bag will cover 0.3m2 (25 bags will cover 7.5m2). For a 5cm deep layer of mulch, one 30dm bag will cover 0.6m2 (25 bags will cover 15m2).

How to mulch

* Before applying mulch, hoe the ground lightly to improve ventilation.

* Never apply mulch in beds planted up with seeds, which need light and oxygen to germinate.

* Leave a space around the trunks and stems of trees and shrubs.

* Sandy soils need a much thicker layer of mulch than clay soils.

* As organic mulches break down in the decay process, they will need to be replenished. Compost decomposes in two to four months, whereas bark chips last about two years before being broken down. - Weekend Argus