The invertebrates and microorganisms in the compost pile require nutritious foods to perform their functions. Providing them with plenty of energy-giving carbohydrates and health-promoting proteins, as well as vitamins and minerals, will keep them working efficiently. By keeping the decomposers well fed you will also be providing food for larger creatures such as toads, which eat them in turn.
Just like humans, the inhabitants of your compost heap thrive on a balanced diet. The invertebrates and microbes require carbohydrates (compounds of carbon, hydrogen, and oxygen) for energy, proteins to build and repair cells, and vitamins and minerals to keep them healthy. Compost experts describe the perfect recipe for decomposers as being like a cheese sandwich: you need carb-heavy bread and protein-rich cheese, perhaps with slightly more bread for a good balance. The air-filled bread also complements the denser composition of the cheese to form an agreeable structure. The same is true of a compost heap, where layers of carbon- and nitrogen-rich materials create the optimum conditions.
The carbohydrates in a compost heap come from woody materials such as twigs, straw, autumn leaves, and bark, as well as household items, including paper and cardboard. The surface area of these carbon-rich foods determines how quickly they will be ingested by the decomposers—for example, fungi and actinomycetes consume paper and cardboard, which have large surface areas, faster than woody stems. The plant materials also contain tough cellulose and lignin that take the microbes longer to process. The decomposers release carbon dioxide (CO2) through respiration, just like we do; about two-thirds of the carbon is lost in this way, while a third remains stored in the compost.
TOP TIP Speed up the composting process by chopping or shredding woody waste such as tree and shrub prunings. Do not compost logs—instead, stack them up in a quiet corner to create a wildlife habitat.
Cell repair and growth is powered by proteins, which the decomposers find in soft green plant material such as grass clippings, young leaves, flowers, and weed seedlings, together with kitchen peelings, cooked vegetables, animal manure, and dead insects and other invertebrates that inhabit the compost heap. These materials also contain a rich supply of vitamins and minerals, some of which are processed by the decomposers and released into the compost as plant nutrients. Not surprisingly, the more varied the ingredients you throw into your bin, the wider the range of nutrients will come out of it.
Bacteria and fungi, which perform the lion’s share of the decomposing in your bin, live in a thin film of water that covers the compost particles. The invertebrates also require water and will die if your heap dries out, so make sure that the ingredients are damp, but not waterlogged—a soggy heap will drown these creatures and push out the air they need to breathe. (see Water and Oxygen) Leafy plants and kitchen scraps usually contain enough moisture to keep the decomposers in a compost heap happy.
Just as all animals, including humans, need a constant supply of food to live, the decomposers in your heap also require a stream of ingredients to keep them active. That does not mean you have to add materials daily or even weekly, since the average compost heap can provide food for decomposers for many months (or even a year if it is a cool heap). Most people with just one heap include ingredients in batches, which means that the top layers may not be fully digested by the invertebrate- microbe populations when the bottom layers that have been worked on are ready to use. You can put this undigested material to one side when you remove the mature compost, and then simply add it to the empty bin to be processed with your next batch of ingredients. The finished compost will still include organic matter in which soil microbes and some invertebrates are still active, which is why it is really a matter of opinion as to when the process is complete.
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