Balancing Greens and Browns
“Compost happens” (and if you search the net you can buy the tee shirt) but in actually only happens due to the work of millions
of compost creatures from bacteria and fungi to worms. Like all creatures they need food and the right conditions e.g. warmth air and water to and turn the waste organic matter into friable earthy compost. Our compost creatures need a source
of nitrogen and carbon.
We divide compostable materials into two main groups Greens and Browns. The Greens are a good source of Nitrogen having a low Carbon:Nitrogen ratio. You may see this in books
and leaflets as the C:N ratio. If you are interested in the technical bit Greens have a C:N ratio of less than 30:1 while Browns, beging high in carbon have a C:N ratio of more than 30:1. You do not need to remember this tc produce good compost! There is more
about the C:N ratio and the carbon nitrogen content of different materials on the Compost C: N Ratio
High in nitrogen, they also tend to contain most moisture. Put simply the Greens provide nutrients and moisture for the compost workforce. Examples of greens from the house are vegetable peelings, lettuce leaves, banana skins and coffee
grounds. Greens from the garden include vegetable "tops", grass mowings, nettles, comfrey, annual weeds and old flowers. Greens decompose quickly.
High in carbon the Browns decompose more slowly and provides the energy for thesource for the microbes that carryout the composting process.
Browns also provide the means of absorbing
excess moisture that would be produced if greens were composted alone. The browns facilitate air-flow within the heap so as to enable the activity of aerobe organisms within the pile. If it is low in browns and it becomes a compacted mess which air cannot
penetrate anaerobic micro-organisms take over and produce a smelly mess often found if too much grass is composted. Examples of browns include cardboard and shedded computer paper from the house and, from the garden, potato, pea and bean hulms, stems
of brassicas and hedge clippings (preferably shredded)
There are various methods for calculating the Green: Brown ratio but for home composting the current advice is to use about equal amounts of Greens and Browns. For gardeners
the Browns, e.g. Tough vegetable or flower stems, old bedding plants, shredded or small pieces of hedge clippings and old straw can be considered as a single group containing material that is slow to rot. However when dealing mainly with
garden waste it can be helpful to sub-divided the Greens into two groups so that the quantity of Browns to be added can be adjusted to prevent the Greens becoming wet and smelly. Group one consists of those that rot quickly e.g.
grass clippings, comfrey, nettles, young annual weeds and plants, and poultry manure while the second intermediate group which takes a little longer to decompose such as coffee grounds, cut flowers, vegetable leaves
and trimmings, rhubarb leaves, soft hedge clippings
Bin Size Matters
different types of compost heap elsewhere but at this stage it is important to make the point that a heap or bin should be at least 1 cubic yard (3’x3’x3’) so that it retain the heat necessary for the composting process to operate effectively.
Smaller bins will still work but more slowly. Composting will still occur in smaller piles, it will just take longer to produce a finished product.
If possible the bin or pile should be located in a sunny well-drained
area while accepting that in very hot weather it may be necessary to add water keep it from drying out. Some bins such as the Green Johanna like shady areas of the garden.
Many people will purchase their
first bin through the scheme operated in conjunction with their local Council without thinking of the volume of waste they produce. This is perfectly acceptable but it is quite interesting to carry out a simple waste audit. If you use a kitchen caddy it is
easy to calculate the amount of kitchen waste produced in an average week. If you do not have a caddy use a plastic bucket. Having estimated you wet kitchen waste. It is then easy to calculate the amount of browns required on the basis of either equal ammounts
of Greens and Browns or 1 part food waste to 2-3 parts Browns (card and paper waste) depending on the materials you are composting. If you have a garden the quantity of garden waste can also be calculated during the growing /harvesting season using
the bucket method with one bucket for green and one for browns. From these calculations you can estimate the size of compost bin or heap required. Alternatively you can be like the rest of us and keep buying/making bins as the compost bug takes hold.
Cool or Hot Composting
Composting is cool or at least the method of composting used by most people is known as Cool or
Passive Composting because the heap does not get, or remain, at the high temperatures that can be achieved with the quicker but more labour intensive Hot systems.
Hot or cold
We look at different composting systems and containers later but whether you opt for a pile, heap, wooden, brick or plastic bin you will as with much of life you will need to start at the bottom and work your way up. Hot composting
using traditional wooden bins is usually based on regular turning of the material best acheived by moving the composting material between 3 or 4 bins. Hot composting can also be acheived using a commercially available insulated bin, such as the Hotbin
or a tumble bin e.g a Jorra
Starting at the Bottom
It is generally accepted that we should try to provide a good airflow to ensure
aerobic composting (this may need to be reduced in the winter if the air temperature drops) and this can be achieved by standing the pile or bin on a pallet base, however this may restrict access by worms if there is a gap of 6” across the whole of the
base so you might consider filling parts of the pallet with earth. Adding sticks to the bottom 6” of a bin placed directly on the soil is also suggested as a way of increasing airflow but remember that this may cause problems if they are to large and
you intend to empty the bin using a spade and the hatch provided in many plastic bins as the wood may make removal of the finished compost difficult. If this bothers you use any coarse “browns” such as straw, corrugated cardboard (exclellent
as it traps the air), scrunched up cardboard boxes as an alternative to twigs directly onto the soil.or be added to them twigs This problem can be overcome if the bin does not have a base by lifting the whole of the bin off the pile of compost to harvest the
compost (and if you are keen to aerate it at intervals).
It helps if the material being put in the bin is layered using alternative layers of browns and greens. This is not so important with modern
cold composting systems but even if you are just going to chuck waste in as it arises it is good to start with a layer of browns. Once you get going you can make adjustments by eye i.e. if it is too dry add greens if too wet add browns
Next add a layer of Greens. Continue as adding material as waste becomes available it is not necessary to add separate layers of greens and browns (aerating the heap or bin will mix them anyway so if you find adding a mix of greens and
browns as they become available do so) but what ever you do you need to keep the ratio of greens and browns right otherwise the material will become wet, black and smelly, of just sit in a dry plie doing nothing other than proviing a dry home
to rats and mice. You can keep the number of flies and other insects to a minimum by always covering the layer of greens with browns until the bin is full or the compost in the bottom of the bin is ready.
If you are happy to wait a year or 18 months compost will indeed just happen in the bottom of the pile. If you need a quicker turn round because of lack of space, more time to manage the system or a modern bin which provides
some form of insulation and aeration you could have compost in a couple of months. Aerating the bin or heap will speed the process and depending on your choice of bin this can be down manually by forking, manually but with less effort using an aerator in a
modern bin or by tumbling or rotating the bin.
If you have a wooden bin with a removable front of a plastic bin with a large opening at the base e.g Komp 250 or Hotbin it is easy to inspect and remove the finished
compost through the hatch. If you bin only has a small hatch and no base it may be easier to lift the bin off the compost leaving a exposing the compost. The top layers will not have composted and should be returned to the bin if the material
at the bottom of the pile has composted use it on the garden.
Ensure that the material returned to the bin is mixed well (aerated) and add water if it was dry Some composters use this process of removing the bin, mixing
the compost and returning it to the bin at regular intervals to aerate the contents and speed up the composting process.
The Hot Heap
Many of us older composters
may remember steaming compost heaps in the gardens of the "big house" or may have seen them on visits to National Trust properties. We can use Hot syatems at home but they require more work and operate best if a batch of three bins are used. We will look at
these systems in detail elsewhere.
To start a hot heap you will need to collect enough material to fill your compost bin at one go. This will require somewhere to store the material before it is added to the compost bin
In order to increase aeration it the tougher items such as stems should be shredded or chopped up using a spade, shears or secateurs. The green and brown ingredients should be mixed, either before or as they are added, and watered. The heap will heat
up within a few days and then after a week or two start to cool down. You can measure the temperature with a thermometer of leave a fork in the heap for a couple of hours. If when you remove the fork you can hold the prongs it is time to turn the heap.
From which you can conclude that if it burns your hands everything is fine!
Once cooled the contents of the heap are normally turned over into a second bin putting the material that was on the outside trying in the
centre. Water is added if the contents are dry, and more browns if it is wet. The aerated bugs in the heap should burst into life and the heap will heat up again. Repeat this turning until there is little or no heating of the pile. Hot Composting can be achieved
with a single heap but mixing the content is more difficult. However turning the heap is the key to quick composting.
We will consider some of the traditional methods of composting before looking at the range
of modern bins available.