Adding Organic Matter to Soil

The worst problem facing gardeners in Australia today is that when soils dry out, they can become water repellent, or hydrophobic. When this happens, water just runs off instead of soaking into the soil.

Hydrophobia usually occurs in sandy soils and often it is caused by mulches. When uncomposted mulch sits on the surface of the ground, waxy, oily material leaves that mulch as it breaks down and coats each individual grain in the soil. When the soil dries out and you try to rewet it, the waxy, oily coating on the grains won't let the water back in and the soil stays dry.

If you took that same mulch and put it into a compost heap, micro-organisms such as bacteria and fungi would break down the waxy and oily material along with the organic matter. As well, the remnants of organic matter that you get at the end of composting actually aid the soil to form tiny little cracks that allow water to penetrate - drying out is never really an issue and the soil always rewets. So organic material used as a mulch causes the problem, but solves the problem when used as a compost.