Why Organic Compost is Important for Your Garden

Every garden must have a compost heap. This is the ideal way to return as much organic matter as possible to the soil, following nature’s example. Decomposing vegetation provides a home for millions of soil organisms, it opens up the soil, improving drainage and easing the way for root growth, and it helps over-drained soils hold water and therefore nutrients.

The plant remains that you gather from the garden in the form of waste leaves, stems from vegetables, grass cuttings, and annual flowers at the end of the season, all contain a great deal in the way of plant food and should not be wasted. However, dug in immediately, this material would initially do more harm than good.

The problem is that the rotting process is carried out by bacteria. Millions and millions of them begin to feed on anything that has just been removed from the soil. In order to carry on the decomposition, these bacteria need nitrogen, a very important plant food. If the garden waste is dug in "green," or in an unrotted state, the bacteria will draw the nitrogen from the soil for their own use, leaving growing plants desperately short of food.

If the plant material is turned into compost before it reaches the soil, it will actually add nitrogen. This is because, after the initial rotting, a species of bacteria known as Azotobacter is attracted by the resulting conditions. These useful microorganisms can "fix" the nitrogen from the air—that is, they take it and convert it into a form that can be used by plants.

So good compost, though not especially high in nitrogen, will at least not take any nitrogen from the soil. The rotting, or composting, process takes time and a successful, well-planned organic garden should therefore have at least two compost heaps. That way, the contents of one heap can be left to rot down properly, while the other is being filled up.

What Not To Include In The Compost Heap

• Any material infected with a persistent disease, such as clubroot or blight—this should always be burned.
• The top growth of main crop potatoes. These should be burned after digging the potatoes because they may infect the heap with potato blight spores—a completely clean crop is rare.
• Prunings from woody plants, because they take too long to rot.
• Cooked kitchen scraps; they often putrefy and will attract vermin.
• Roots of pernicious weeds such as couch grass (Agropyron repens), ground elder (Aegopodium podagraria), bindweed (Convolvulus arvensis), and creeping buttercup (Ranunculus repens). These must be burned immediately as they will only multiply in the compost heap.
• Any weed seeds. You will often read that the heat of the compost heap will "cook" all the weed seeds rendering them unviable. This is true only if the heap reaches a very high temperature. In fact, a heap will only get hot enough to kill most pests and diseases but not seeds. They remain dormant until the compost is spread and end up high enough in the soil to be able to germinate. However, weeds pulled up before they seed, or even flower, should be added to the heap.