Why make compost?
Wouldn’t it be simpler to lay undecomposed matter on the surface than to bother making compost? This method is called 'chop and drop', and in dry climates, it may be the best course to take.
However, in damp climates, having undecomposed waste on the surface can attract slugs and can be disastrous for vegetables.
An advantage to composting is that decomposition occurs quicker in heaps. These heaps are more than just 'decaying material' because they convert waste matter so quickly into stable organic matter (humus).
Albert Howard, who pioneered new ways of compost making in 1920s India, found that heaps could contain more nutrients available to plants than were in the materials added. He also created compost in pits to conserve moisture but made heaps during the monsoon. The lesson here is to adapt your method to your location.
A balance of green and brown
Why differentiate? Well when you achieve the desired balance of about 50:50 by weight, this means you probably have the correct level of moisture, warmth and structure in a heap.
The result is that you get decent aeration and sweet compost, rather than being sour and anaerobic, which often results from adding too much green.
An excess of green can result in high heat, bacterial dominance and a lack of air.
In contrast, a dominance of brown materials results in less warmth, more fungi and a slower process.
- Green ingredients are soft, leafy, high in nitrogen, usually moist, and low in fibre. Kitchen peelings, grass, weeds and food wastes are mostly green.
- Brown ingredients are fibrous, drier and woodier. They include soil, paper, old tree leaves and straw.
Some materials are both green and brown, such as broccoli stems and wood 'of the season'; i.e. the green but firm stems of new-season growth on any woody plant. There are also some green ingredients such as coffee grounds and horse poo (both 3% nitrogen) that look brown.
In Somerset, elder trees grow fast in hedges, and we can cut new growth of 2m length, then shred it for composting in late summer.
Temperature - does a heap need to be hot?
Heat is not vital. You can make excellent compost, albeit more slowly, at temperatures of 30-50C/86-122F. To check the temperature, you can buy a compost thermometer, like the ones in my photo, online.
This temperature probe is 30cm long and shows 70C in the heap with a mix of green and brown. This was in April and we also added grass clippings.
These are some differences between compost from colder and hotter heaps:
- Temperatures below 55C/131F do not kill weed seeds and decay in a more fungal manner. They may also contain more beneficial microbes, depending on what you need.
- Warmer heaps decay using bacteria, especially when temperatures are over about 50C/122F. Large compost making companies often achieve temperatures of 80C, turning the colour to black, almost like charcoal.
- Cooler heaps result in browner compost and take longer to decompose.
- The higher microbial count from cooler heaps is excellent for soil biology.
My compost heap averagely four months old, was turned six weeks ago and is now 30C.
It is not vital to do this.
However, doing so often improves quality by adding air and mixing lumps. For small heaps, you can use an aerating tool to lift and mix within the heap, without moving its contents.