WHY MAKE COMPOST?

"Why would you want to deny the Earth your cauliflower stalk?" – Satish Kumar

At the end of a meal, many leftovers go straight into the bin along with any peelings, etc. from preparing the food. We currently throw away a third of the food we buy, but the tide is turning and more and more people want to grow their own food in healthy soil, and reduce their waste, which is why making compost is so important.

Whatever type of soil you have, compost will improve it. I've heard people talk about how compost is only a 'soil conditioner', as though somehow this was not really important. I think they mean that compost does not add much in the way of nutrients to the soil, but this is not the point. Soil conditioning really means adding humus to the soil. Humus is stable organic matter in the soil and it acts like 'glue', holding on to nutrients and water. In effect humus adds life back to the soil: doing this is the most important thing that we can do for the soil and it's ridiculously easy.

Compost has some nutrient value too, mostly held by the microbes that have proliferated during the composting process. The following are just some of the benefits of adding compost to your soil.

Healthy soil

Compost adds life in the form of microorganisms

Using compost on your soil will dramatically increase the amount of life in that soil – both life that is visible to the naked eye and, more importantly, life that can be seen only through a microscope. The addition of compost builds a healthy soil and so boosts the microbial activity, which provides food for hundreds of thousands of different species of fungi, bacteria and other organisms; these microorganisms are also food for a whole range of other organisms, which in turn are fed off by predators. What we can see when we look at compost are the creatures, mini-beasts on the macro scale; you will need a magnifying glass to see the very small ones, but many are obvious and well known to us. See 'More wildlife', page 18, for more on this.

Crucially, this microscopic world is cycling nutrients from the compost materials into a form that the plants in our gardens can easily assimilate, and holding them in the soil until the plants need them. Of all the soil organisms the worm is the one that we all recognise as invaluable for creating a healthy soil, and it does indeed possess almost miraculous powers – both the compost-dwelling species and the larger soil dwellers – but in fact it is the whole complex web of life in the soil that is kept vibrant by regular additions of compost.

Compost changes the physical structure of the soil

The humus that remains when compost has been further broken down in the soil coats the soil particles and creates the crumb structure that allows the exchange of gases and liquids. So in sandy soils compost increases not only the water-holding capacity but also the nutrient-holding capacity of the soil. In