Other than carbon dioxide and oxygen from the atmosphere, and energy from the sun, plants get everything they need for growth from the soil, including water and nutrients. Organic methods involve ensuring the soil is healthy, water-retentive and replenished with nutrients naturally. Almost all soils, whether sand, loam or clay, will benefit from increased amounts of organic matter, and one of the main ways of producing this within a closed-loop system is making your own compost.
All gardens should have a compost heap or container, however small. To throw away your kitchen waste, weeds, grass-mowings and so on, is to throw away valuable fertility. There are numerous composting bins, cages, tumblers and containers available, many of which are suitable for small plots, but it’s better to make your own if you can, using old pallets or other reused materials. If you have the space, the ideal is to create two or three bins or bays so that one is the freshest you are adding new material to, while the others are rotting down.
The speed at which compost becomes usable depends on the size of the heap, the type of materials added, how hot it becomes and how often it is turned. Small heaps may produce very little heat and will rely on the action of many creatures to break it down including worms, millipedes, woodlice and slugs, as well as many different types of bacteria and fungi. Obviously it’s best if these heaps are built directly on to the soil so that the creatures can get access to the material.
Larger heaps with the right mixtures of materials can produce a significant amount of heat caused by the action of bacteria. These can rot down much more quickly and have the advantage of killing weed seeds and many pests and diseases if the temperature gets above 60°C. There are also specially insulated ‘hot bins’ available which create this ideal set-up with smaller amounts of compost. Even with a simple heap though, turning the compost with a garden fork will mix the contents and speed up the process. This can be done anything from weekly to every month or so. A heap that is regularly turned and reaches a good temperature can break down in as little as a couple of months, but in practice many heaps are left for longer, often a year, before being used in the garden.
One key aspect is the mix of materials added. Many garden heaps are made up largely of grass-mowings, weeds and kitchen waste, all of which are rich in nitrogen and known as ‘greens’. The ideal compost, however, will be produced from a mixture of roughly two-thirds greens and one-third browns. ‘Browns’ are carbon-rich and could be made up from straw, stems such as spent tomato vines, woodchips, sawdust, torn-up cardboard and shredded paper. Add these in layers with your green material as you build the heap up, and if it is too dry, water with rainwater before covering the heap with something like a piece of old carpet to add some insulation and stop it drying out.
Once the compost has rotted down to a brown crumbly texture, it can be spread around the garden beds as a mulch (see below), used in trenches for crops like potatoes, to fill raised beds, or sieved and mixed with soil to make a growing medium for pots. Composting can be a complex process with many different schools of thought; there are plenty of books and articles on the subject should you wish to investigate in more detail.
A small number of leaves can be added to the general compost heap and mixed in, but if you have a few deciduous trees, the large quantity of leaves will rot more slowly, so you will be better off building a leafmould pile. This needs to be open to the elements and can be as simple as a circle or cage of wire (reclaimed chicken wire, for example) which you fill up with the collected leaves. Depending on the type of leaves, they may take as much as three years to break down to a brown crumbly texture. This can then be used as a mulch or as part of your growing medium for pots and seeds trays.