Marvellous mulch

What is mulch?

We all know mulch is the stuff we put on our gardens – but it’s so much more! It’s usually made from chopped up branches and trunks, but there are many other organic and inorganic options. Their specific qualities make them suitable for different applications, such as ornamental beds, vegie gardens, underneath trees and in bare areas.

What does it do?

One simple act of mulching covers many tasks. It starves weeds of sunlight and air, slows water run-off, and reduces evaporation, keeping soil moist. Over time, it helps to improve the structure of clay, which facilitates air and water movement through the soil. It adds nutrients and structure to sandy soils. Mulch reduces erosion and insulates soil, benefiting plants and soil organisms such as earthworms. It can also take our gardens from drab to fab, providing a neat and finished look.

How to mulch a garden

Organic mulches include lucerne hay, pea straw, sugarcane and bark chippings of various sizes. These decompose at various rates and are the most common, cost-effective mulches. Apply in layers 5–10cm deep in new areas, and 5cm deep when re-mulching. A layer that’s too thin will need topping up more quickly and will allow weeds and grass to grow through. A layer that’s too thick lasts longer but doesn’t allow water through, and your plants will suffer.

Inorganic mulches don’t decompose and can be relatively expensive. They include gravel, pebbles and scoria. Used judiciously, they can become a feature, and they’re practical near buildings in fire-prone areas, or for indoor plants.

Whatever you apply, it’s essential to weed the area first, by hand for small areas, or with a whipper-snipper or mower for large areas. In garden beds, water and fertilise plants before laying cardboard or newspaper, then mulch. Avoid plastic weed mat because, while it deters weeds underneath, it provides the perfect moist environment for blow-in weed seeds that, once germinated, are difficult to remove.

Use the same method when mulching excessively weedy areas or creating a new garden bed on lawn, but apply the mulch 10–15cm thick. Allow 3–6 months before starting to plant up the new area.

Not all ornamental plants need mulching. Desert plants, for example, grow best with gravel mulch or nothing. Organic mulches create a more humid environment than arid species are used to, and can cause fungal problems to develop. Always consider where your plants grow naturally.

Mulch can be applied and reapplied at any time of year in most areas, although gardeners in the wet tropics should wait until the end of the wet season. If plants that like dry conditions receive excessive rain, rake mulch away to allow soil to dry. In cold areas, remove mulch from vegie beds in early spring to warm the soil.

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