Composting Techniques

With composting going peat-free in 2024 purchased compost is likely to increase in cost and be of lower quality
The science is not well agreed but, with 3 times as much carbon in soil as in the atmosphere, it is likely that composting on-site will retain carbon in the soil and help reduce global warming.
Composting on your allotment reduces the time and effort of wheelbarrowing away waste and bringing compost in.
Crop yield is better when using compost.
Your compost is free apart from some personal effort.

A range of different techniques are described below.

FLAG members have now established compost bays at both ends of the Folly Lane site. There is also a wood holding bay the contents of which are burnt when we next have a site bonfire.

The bays fill up fast with good compostable material but also items that will not break down easily.

So please do not add branches, brambles or prunings to any of the heaps. Either burn these items on your own plots or keep them until we have our next FLAG bonfire.

1. Cold Green/Brown composting.

Put green and brown (brown Is cardboard, small parts of wood chips, thin twigs, leaf mould etc) waste into an area without any particular preparation and leave for typically something between a year and two years. This is the process followed on the site's communal compost heaps.

Pros:

Low effort/requirements of compost bay building. It could just be a heap or simple pallet structure.
The low effort involved in material preparation.
No ongoing compost heap maintenance.
Not necessary to turn.
Can deal with medium to small wood chips that are not necessarily old.

Cons:

It can take a year or two to compost down.
The process does not kill all seeds and some roots. You will need to hoe and weed after compost use.
Some people would segregate out seeds, bind weed and the like before putting in a cold heap. This is a time consuming process.

For more information and a video, click here.

2. Hot Green / Brown composting.

Put green and brown items after chopping into small pieces (Inches long) in layers into a large (about 1 m-sided cube or larger). compost bay with insulated but air porous solid sides, ( eg lined with tape/ink/staple-free cardboard). Cover with a moisture barrier and with rain protection. Monitor temperature and water as you build and over time to maintain a minimum of 40C and a maximum temperature of 70C. Probably you will need to add water as you build. Turn into a second bay once it cools below 40C, altering water content as needed and putting less composted materials in the middle of the heap.

For more information and a video, click here.

Pros:

Quicker process, 6 to 9 months.
A temperature of above 55C kills seeds and roots.
If built-in a Polly tunnel/ greenhouse provides free winter heating for early plant germination.
Only turned once to balance benefits versus effort.
Apart from wood and bramble roots, everything goes into it. So, weeding becomes a positive experience as you are creating compost and feeding your “beast”.

Cons:

The effort and space to set up the compost bays. You need probably 3 bays for a half allotment.
The effort to prepare the materials going in.
The effort to turn.
The effort to monitor and manage the temperature. (above 70C the bacterial reaction it depends on is killed). If they get too hot it’s recommended to create vertical holes in the heap and inject water.
The process is too fast to deal with anything except the smallest wood chips. Wood chips need a slow, long process to break down the woody lignin structure.
Wood chips should be part rotted, at 6 to 9 months old, and small when going into the system. (Wood chips should be stored with access to air to prevent anaerobic decomposition that creates methane. (Very bad for global warming))
The leaf mould used should be pre-rotted from last year.

3. Farmyard manure.

Apply 6 months or older rotted farmyard manure. Must be from animals fed on grass/ hay where weedkillers have not been used. Can be added to a compost heap.

Pros:

Rich manure that gives good plant growth.
Some farmers offer it free on collection.
No compost bays are needed except for possible space for a heap to mature in if too fresh on collection.
No maintenance effort.

Cons:

You probably have to collect and bag yourself.
The risk that the animals had been eating feed where weedkillers have been used. Weedkillers can be retained in the manure for years and it will then kill your crops OR STUNT THEIR GROWTH FOR YEARS.
If used fresh can damage plant growth.

4. Multiturn hot green/brown composting

This is best done using a commercially sold insulating drum turning device which is turned every few days

Pros:

Fast composting process.

Cons:

Requires a lot of turning.
Usually quite small.
Hot multi-turned compost is best left for some months after the turning process is complete to give the best plant growth.

5. Cold damp woodchip fungi compositing in the Johnson-Su bio reactor principle.

A specifically configured heap is required with air gaps under and through it, water impervious surround, and routine light watering. The compost from it is claimed as giving excellent crop growth.

For more information and a video, click here.

Pros:

A great way of transferring wood into compost quickly
Quite a low effort once built
Uses wood chips that we have lots of.
Produces a fungal dominant compost that is quoted as giving good plant growth. It is also supposed to be good for soil carbon retention.

Cons:

Complicated to build (Wood chips have to be soaked before incorporation in the heap).
About a one-year decomposing period.
Needs a routine watering applied theoretically daily
Best to start with selected small wood chips.
If accidentally done without air circulation could lead to methane production.

Tim and Liz on 31w are trialing a hot green/brown compost heap (no:2 above) & a version of a Johnson-Su Bioreactor (no: 5 above).