Balancing Greens and Browns
“Compost happens” (and if you search the net you can buy the tee shirt) but in 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, mainly materials that are green in colour, 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( mainly brown in nature) being high in carbon have a C:N ratio
of more than 30:1. You do not need to remember this to 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 mowing’s, nettles, comfrey, annual weeds, and old flowers. Greens decompose
High in carbon the Browns decompose more slowly and provides the energy for the source for the microbes that carryout the composting
Browns also provide the means of absorbing excess moisture that would be produced if greens were composted alone. The browns facilitate airflow within the heap 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
shredded computer paper from the house and, from the garden, potato, pea, and bean hulms, stems of brassicas and hedge clippings (preferably shredded) and woodchip.
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
We consider different types of compost heaps and bins 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. If the bin of heap is too large, anaerobic zones may occur in the central core or in undisturbed areas which will slow the composting process and
create cooler areas as the material ferments. If the bin, heap, or windrows are too small they will not retain sufficient heat to kill pathogens and weed seeds or to evaporate the moisture. In such heaps aeration by turning is more important than
in a small cool composting bin.
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.
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 your wet kitchen waste. It is then easy to calculate the amount of browns required on the basis
of either equal amounts 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.
The porosity of the materials will also influence the composting process, air spaces being central to effective aerobic composting. Small particle size, tightly packed materials can lead to the
air spaces being filled with water resulting in anaerobic conditions. while the feedstock sis often cut into 1-22 lengths for composing very small particle sizes will reduce the number of large pores and restrict oxygen distribution. minimizing
heat loss, larger piles are suitable for cold weather. However, in a warmer climate, the same piles may overheat and in some extreme cases (75 °C and above) catch fire.
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 achieved by moving the composting
material between 3 or 4 bins. Aerating, by turning and moisture levels, influence the time taken to create compost. Turning every two days can produce water in about a month, turning weekly can produce compost in a month or two while
monthly turning can complete the process in four to six months, If the contents are not turned composting can take between a year and 18 months.
Hot composting can also be achieved using a commercially available insulated
bin, such as the Hotbin or a tumble bin e.g. a Jora.
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 bas. 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 too 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 woodchip, straw, corrugated cardboard (excellent 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 whatever 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 providing 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.
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 systems 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.
homes greens will be readily available in the form of kitchen waste throughout the year but browns from the garden may need stock piling for future use. Autumn leaves can be collected and stored in a loose pile in dry place, prunings can be shredded as they
become available and the woodchip stored in a dry place, woodchip or sawdust may be collected from local sources or from the council on an informal basis. Hay or straw can be collected from a local farm or pet shop. Cardboard and shredded paper may be available
from l;ocal offices or shops.
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
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.