Composting recycles organic waste into a product that makes garden soil healthy. Mature compost is a dark brown, sweet-smelling material that can be added to topsoil.
There are two ways to make compost – aerobic, which requires aeration during the process, and anaerobic, which is a slow, rather smelly process. Mature aerobic compost can be produced in about 6–8 weeks in most areas of Australia.
How does compost make garden soil healthy?
- Compost keeps soil more moisture-retentive, yet better-drained.
- Compost provides food for earthworms that increase the depth of fertile topsoil by leaving digested food along their deep tunnels.
- Compost provides food and a home for the many helpful bacteria and fungi that help protect soil from soil-borne diseases.
- Well made compost has a pH of 6.5 – where all plant nutrients are fully available, and the perfect pH for the majority of plants.
- Compost buffers plant roots from an unsuitable pH in surrounding soil.
- It also insulates plant roots from temperature extremes so that soil stays cooler in summer and warmer in winter.
- Compost contains all the minerals that plants, animals and humans need for good health, most of the soil’s nitrogen, plus lots of humus that forms the most stable part of recycled organic waste.
- Humus and the minerals that plants need both carry a weak electrical charge. The electric charge holds the plant food minerals close to plant roots and prevents them from washing away in heavy rain.
- Humus is able to control the release of trace elements needed in tiny amounts, and block absorption of poisonous metals in soil so that they do not end up in our food.
- Humus stores carbon in soil for very long periods of time.
- Humus, in compost, provides a habitat for a soil community of billions of beneficial bacteria and fungi that perform important functions.
- Some bacteria species in humus make a ‘glue’ that is able to hold soil particles in a way that improves the flow of water and air through soil. This improves the structure of soil so that plant roots grow more easily. Strong roots help plants to resist the effects of drought and storms.
- Mycorrhiza fungi in humus stick like hairs to the roots of plants, helping them absorb water and nutrients in exchange for sugars produced by plants during photosynthesis. Some 95% of perennial plants rely on mycorrhiza for healthy growth.