By Keith Jordan
As October day lengths shorten and the sun is lower in the sky, temperatures are generally on the decline. This is a natural trigger for many animals and plants to make provision for storage and survival during the winter months. Jays and squirrels will be collecting acorns to bury, insects may be laying eggs, pupating or finding safe hibernation places. Many herbaceous plants die back, shed leaves or divert their energy reserves from leaves and stems to their roots, tubers or bulbs.
Associated with mass decomposition of plant material, well-made compost heaps will be warming up. Decomposition involves millions of microorganisms (bacteria and fungi) plus some larger organisms including earthworms, molluscs and woodlice. Under optimal aerobic conditions, composting proceeds through three phases:
1) Mesophilic phase (moderate-temperature), which lasts for a few days (look out for woodlice and worms). Composting will occur optimally if the mixture of materials is right – a good mix of greens (the wet, soft, green materials, high in nitrogen) and browns (the dry harder, absorbent materials high in carbon). It needs to be moist (water if necessary, but not too wet) and have enough air (some bulky, twiggy material provides this). Covering with old carpet will help to keep the heat in.
2) Thermophilic phase (high-temperature), lasting from a few days to several weeks depending on the time of year and material. Billions of bacteria (good species!) and fungi will chemically break down the variety of organic materials, using a broad range of enzymes, and generating heat in the process. You may have seen evidence of this exothermic process – steam rising from a heap of manure on a cold day. This is the basis of the old technique of hot beds used in the walled kitchen gardens of stately homes to raise plants in cold frames out of their normal season.
Larger, insulated compost heaps may heat up to 40-50°C and municipal scale compost systems to 60-70°C destroying pathogens, fly larvae, and weed seeds. It would be interesting to use a thermal camera to check yours! Mix grass clippings, straw or hay to kick start slow, cool compost heaps. Natural products high in ammonia can also help (e.g. poultry manure, waste water from an aquarium, etc.).
Lack of oxygen (if too wet or compacted/ perhaps too much soil added) results in anaerobic bacteria producing ammonia and hydrogen sulphide (smelly and no heat!).
3) Cooling and maturation phase, lasting several-months. Woodlice and worms carry on the process.
Turning material once or twice will help this stage. The result is nutrient rich organic matter, perfect material for adding to your soil, making potting compost and mulching around plants.