In order to make high-quality compost without running into trouble, you really have to ‘use’ your compost bin, and use it effectively. This means taking several measures.
Methods of Composting
To begin with, two methods can be used to make compost: the Batch Method and the As-You-Go Method. Here’s how they work:
The Batch Method is a two-step method such that first you prepare the pile by putting in the materials and contents that are to be composted, and then you ‘cook’ the whole thing as a batch.
In contrast, As-You-Go is an iterative method in which adding composting materials and the ‘cooking’ occur without discrete steps as a single ongoing process. Compost bins are ideally suited to As-You-Go Style composting while compost tumblers are better for the Batch Method.
As this is an instructional article about making compost in bins, our primary focus shall be on the As-You-Go Method.
The Carbon:Nitrogen Ratio
Effective usage of your compost bin requires that you get the Carbon:Nitrogen – C:N – Ratio right. For a compost bin the ideal C:N ratio is from 30:1 to 40:1. The C:N ratio is colloquially but incorrectly also called the ‘Brown-Green Mix.’
Be mindful that C:N and Brown-Green do not have a direct correspondence. This is because, while ‘Green’ compost content has a fairly narrow range of C:N ratios hovering around 30:1, ‘Brown’ content’s C:N ratio and, therefore, carbon content, varies widely. It ranges from 40:1 to 600:1! Also, where composting is concerned, ‘Green’ content includes that which is green in colour; however, material like tea leaves, coffee grounds, and manure are considered ‘Greens’ because of their C:N ratios.
You can hit the desired C:N ratio by following two simple rules. One, strive for a Brown:Green materials 1:1 mix, that is equal parts Brown and Green. Two, be careful with woody and wood-derived materials; use these in very low quantities because they have an extremely high proportion of Carbon to Nitrogen.
Turning and Aeration
Turning and Aeration are crucial to making high-quality compost. You will need to turn and mix up, and thus aerate, your compost pile by using a handheld aerator. Various brands and models of compost aerators are available. Try to choose one that is right for you and also for your compost bin. If you want to be frugal and go low-tech, do as your grandpa did and use a pitchfork.
The reason to turn and aerate a compost pile is that if it just sits then the material near the top will decompose at a faster rate while the material that is at the bottom, and which is being compressed by the pile’s weight, will decompose at a slower rate. Organic materials need air to decompose but materials that are in the middle of the pile or compressed at the bottom would be starved of air. Turning the compost pile means that there is no bottom layer and no top layer, and this agitation ‘fluffs up’ compressed materials and opens up air channels in them.
Vigourous turning will also bring another benefit; it will tear and break up scraps and pieces.
Aerate the pile twice or thrice per week. Also do so when you add a fair quantity of material to your As-You-Go pile in the bin. You can insert your aerator through the built-in holes at the top and/or the sides of your bin. However, you probably will be more comfortable and will be able to do a better job of turning and mixing the compost if you open the lid and use the aerator through this (much) larger opening.
The moisture content of the compost pile is another key to effective decomposition. The pile should remain damp and should never be allowed to dry out because if it does, ‘cooking’ will slow down and the pile will also decompose (more) unevenly.
If, when turning the pile, you observe that it is dry, conservatively water it all over as you turn it such that it is well moistened and damp but not wet.
What can you put in a compost bin?
The short answer: anything organic, because it will decompose.
The best things to put in a bin are old compost, garden soil, garden clippings and cuttings, vegetable and fruit waste, grass clippings, fresh leaves, dry leaves, mulch, kelp and other seaweed, hay, and straw.
Try to chop up or dice big cuttings otherwise they will not decompose as rapidly as you would like. In addition, you can put carefully-selected leftover food scraps, twigs, newspapers, rough (not coated or shiny) cardboard, manure, sawdust, wood chips, tea leaves, coffee grounds, old cotton cloth, eggshells, and peat moss.
Do not add rice or grains, cooked or uncooked, or meat or dairy products. Rice and grains will bring rodents to your compost bin while meat and dairy will attract flies and may well putrefy instead of aerobically decomposing. Newspapers and cotton cloth should be torn into small pieces and soaked or wetted before being added to the bin to promote decomposition.
All wood-based and wood-derived materials have a very high C:N ratio – 400:1 and higher – so be conservative when including such materials. Err on the side of too little of these than too much, otherwise the compost pile will remain dry, won’t heat up, and will decompose very slowly and very unevenly.
How you arrange or layer these materials initially is of some importance. Put a layer of commercial ‘starting soil’ aka compost starter, plain compost, or even plain garden soil at the bottom, and put a layer of one of these same components right at the top. Of course, when you turn and churn the pile after a few days everything will get mixed but ‘layering’ is the way to start off on the right foot. If you anticipate that you may not turn the compost pile for more than three days, put a layer of starting soil (or substitute) on the top.
Weeds are organic plant-based material but if you are new to composting or simply don’t have time for fussing, do not put any weeds in your compost bin. Weeds enjoy warm and rich composting materials so much that they will take root and grow in your compost pile!
On top of that, if weeds go to seed as your compost ‘cooks,’ you could end up with weed seeds in your compost – which means that your nice new compost would sprout weeds. The way to make sure that weeds do not germinate and turn into compost is to ‘pre-bake’ them, or to use the Batch Composting method, turn the pile very frequently, and even monitor the temperature at its centre to be sure it does not drop below 65° centigrade. And for all that, you should not put pernicious weeds, like Bishop’s weed and crabgrass, in your compost pile at all.
If you add manure to your compost bin, do not include horse manure at all. Other types of manure may be added but these should not be fresh but old or ‘aged.’ Fresh manure is simply too hot to add to a compost pile.
What to put in a compost bin when starting
A very good mix to start off a compost bin would comprise of vegetable and fruit refuse, grass clippings, tea leaves and coffee grounds, chopped or torn-up dried leaves, wetted old cotton cloth or some shredded and wetted newspapers – not to forget some commercial ‘starting soil’ aka compost starter, regular compost, or even plain garden soil. While these limited materials in the right proportions make for a very good Brown-Green mix, they are also very readily accessible.
Building a compost bin for grass clippings
Even a novice DIYer can rig up a more-than-passable open compost bin for grass clippings using little more than some lengths of timber, nails, a hammer, and a saw. You’ll need four 100-centimetre lengths of 38 x 38-millimetre timber (“2-by-2s”) and eight 90-centimetre pieces of 38 x 150-millimetre lumber. You can use pressure-treated timber or Western Red Cedar. If you can source the timber at the desired lengths, well and good, otherwise it is easy enough to saw longer lengths yourself. The four lengths of timber will be the upright posts and the eight planks will form the horizontal spans of the bin. Finally, 32 75-millimetre nails (plus some spares at hand) will do it.
Using the saw or a hatchet, sharpen one end of each post to a fair point so that it will be easy to drive the post into the ground. Place two posts parallel on the ground just about 90 centimetres apart and lay two planks across them such that the ends of the planks rest on the uprights. Place the upper plank about 25 centimetres from the top of the posts and the lower plank about 20 centimetres from the upper one. Nail each plank to each of the two posts using two nails per end. Now you have completed one ‘wall.’
From this point you can proceed along a few different avenues; however, try the following steps. Other ways of completing the bin will require the use of a carpenter’s workbench or the assistance of a helper.
Make a second ‘wall’ in exactly the same way.
Now you will be left with four planks.
Press the four posts lightly into the ground so that the two ‘walls’ are 90 centimetres apart opposite to one another. Hold up the remaining four spans against the empty sides to make sure you have the spacing correct, otherwise adjust the posts. Once you have got the spacing right, pound the posts into the ground so that the structure is firmly set.
Temporarily affix any one of the remaining four spans that will make up the missing opposing ‘walls’ using masking tape, duct tape or epoxy glue so that it remains in place. Gently hammer in a nail on one end of one of the spans to get it going without shaking up or bending the post. Then grasp the post from the top, press it firmly downward, and hammer the nail all the way in. Next, using this same method, hammer in a nail on the other end of this same plank. Then hammer in the remaining, second nail on each end of this same plank.
Repeat for the other three planks which will make up the remaining two ‘walls,’ and you have your compost bin.
When you need to reposition your compost bin, do not pull out by holding and pulling the ‘walls;’ pull it out by grasping and pulling up from the bottom of the posts.
Here are a couple of ideas by which you can improve your DIY compost bin.
Attach a layer of heavyweight mesh netting at the bottom so as to make a floor. Additionally or alternatively, hammer in cut-to-size sheets of mesh netting over the open ‘walls.’ This addition would keep rodents out and prevent grass clippings from falling out while allowing aeration. Though mere grass clippings would not attract rodents, heavyweight mesh netting would give you the option of putting other materials in the compost bin.
Instead of nailing in the top plank of one side, screw-in (one leaf of) an appropriately-sized hinge to the leftward post such that the unattached leaf swings outward. Screw-in a cabin hook or eye-latch to the right end of the plank, and then join the blank end of the plank to the hinge. Close this span to mark where the hook will fall on the rightward post, and attach the hook or latch’s eye at the marked position. Now, when you need to shovel out compost, open the top span and shovelling will be so much easier.
How to keep your compost bin from smelling
To keep your compost bin from smelling, first, you need to make sure that the pile will decompose evenly and aerobically, and not unevenly or anaerobically.
To achieve this rather important end, the pile needs to have air circulating within it – even right at the very bottom. Turning and aerating the pile with an aerator will ensure that there is no ‘bottom layer’ as such because the pile gets turned and churned. It also ensures that all the bits and pieces get separated which means that air channels open up throughout the pile, increasing airflow.
Second, your pile’s Carbon:Nitrogen balance should not tip over too far towards Nitrogen which can and does happen when too much ‘Green’ and too little ‘Brown’ is added. Be sure that you keep adding a sufficient amount of ‘Browns’ to balance whatever ‘Greens’ you add.
Finally, some materials are smelly to begin with and are also more likely to putrefy and emit foul odours. These include meat and dairy products and, yes, manures. You can exclude such materials without any negative impacts on your compost pile.
How to get rid of grubs in a compost bin
First, think it over. There are grubs, and then there are grubs. Many of them, like earthworms and microbes, are actually beneficial to your compost pile without ever being harmful, even after you use the compost in your garden. Grubs burrow and tunnel through the pile thereby creating air-channels and doing some of the aeration for you; futhermore, like microbes, many grubs feed on organic materials and decompose them.
Now if you have identified pernicious grubs or that may harm your garden, if your pile is simply infested with grubs, or if it has maggots, then you would need to get rid of them. Buy or order a supply of Beneficial Nematodes. These are available at garden centres and online sellers. Follow the instructions and introduce the Nematodes into your compost pile. Goodbye, grubs.
If your compost pile is on the small side, you could get a bottle of Neem Oil. It works as a natural pesticide against grubs (and even garden pests). Dilute the oil to a strength somewhat greater than what is outlined in the instructions, be sure you have created a good suspension, and spray it into the pile as you turn it.
You could also try to put a bird feeder very close to your compost pile. The birds that you attract may go on to feed on the grubs in your pile!
How to stop flies in your compost bin
To begin with, keep the lid tightly closed. If your compost bin is a jerry-rigged affair and has no lid then cut out the appropriate size of heavy-duty but fine wire mesh such that you can bend the mesh over the rim of the bin and secure it. You will also need to cover the side air vents with a mesh netting.
Flies are drawn to food waste, therefore push all food waste (and whatever else may attract flies) to the middle of the bin. Do not leave such materials at or near the surface. If you are developing a serious problem with flies, eliminate food waste altogether. Additionally, after turning the pile put a thin layer of grass clippings on top; this will not draw any flies.
Rat proofing your bin
As the first step, you can ‘rat proof’ your bin by simple dint of using an all-solid bin made of hard materials and always keep the lid tightly closed such that it cannot be dislodged by these clever and persistent rodents. Cover up any side vents with rat-proof wire netting.
You can ‘rat proof’ your bin’s interior by not adding any materials that would attract rats. These include leftover food scraps, meat, dairy, and eggshells – and you can live without these in your compost pile so nothing’s lost.
To play it safe, keep the pile very much on the damp side. Rats will take to a dry’ish compost pile but not to a damp one.
Put the bin on a concrete slab in an open, unsheltered area that does not provide any cover.
Install an 11-watt daylight LED near the bin and keep it on from evening to dawn.
You may also consider doing what our ancestors used to do in mediaeval times: keep a good ‘mouser.’
If you take all these measures you should never have any rats in or near your compost bin.
Should I put earthworms in my compost bin?
You don’t need to but you certainly may. If you want to put worms in your compost bin, put in red wrigglers. They are perfectly adapted to the conditions of a compost bin and can be seen as “Mother Nature’s Composter.”
As for earthworms, they are more sensitive to the highly variable conditions of a compost bin. Actually, if your compost pile offers conditions favourable to earthworms then they will make their way to it themselves but you can give it a shot and dump in some earthworms and see what happens. If they thrive in your compost bin you’ll have lucked out twice over.
First, earthworms, like grubs, burrow and tunnel through the compost pile. In so doing they too create air channels inside the compost pile, aerating it. Second, earthworms consume much of the materials in the pile. What they excrete, called ‘castings,’ is rich in micronutrients and nitrogen, and is one of the bases for high-quality compost.
Composting with the aid of worms is known as ‘vermicomposting.’
Do compost bins smell?
Compost bins may smell a wee bit, yes. Depending on what has gone into a Batch Style compost heap, it can smell a little initially. And depending on what you may add to an As-You-Go Style compost pile it too may smell a bit. Then again, just as often a well-maintained compost bin will give off a warm, musty, earthy odour that may even be quite pleasant.
Well-tumbled compost in properly-used and aerated bins should not smell particularly bad at all. But sometimes compost bins do smell bad, and when this happens it signifies that something has gone wrong. One reason behind it could be that the compost pile, instead of decomposing aerobically, is putrefying – decomposing anaerobically, i.e. without oxygen which points to inadequate aeration. Another reason behind it, especially if the bad smell is like ammonia, is a seriously out-of-whack Carbon:Nitrogen ratio skewed in favour of Nitrogen. And if you’ve been naughty and went and threw leftover meat or dairy into your bin, well…
How big a compost bin do I need?
To a large extent, this depends on both your gardening and compost needs and on the amount of composting materials you will generate and source. Commercially-available compost bins meant for individual and household use range from a volume of a measly 150 litres up to a huge 1600 litres – a factor of over ten!
Try to estimate the volume of compost you want to make and buy a bin of the appropriate size. If you estimate your volume in litres, it is easy to calculate the overall dimensions of the compost bin you need: simply multiply the litre value by 1000 to arrive at the bin’s size in cubic centimetres.
All that explained, the open bin for grass clippings (and other similar materials only) that is detailed in section Building a compost bin for grass clippings hits the sweet spot at a size of about 770,000 cubic centimetres and volume of about 770 litres. If you are uncertain as to the size of the bin you need, go for one with a volume of between 700 and 800 litres. Even if it seems too big initially, it will give you room to grow as a composting gardener.
Can you put newspaper in a compost bin?
Yes, but in its correct proportion which, in a compost bin, would be in a moderate volume.
They are a ‘Brown’ source and add the necessary carbon to a compost pile but at the same time, the C:N ratio of newspapers at about 200:1 is significantly, though not overwhelmingly, oriented toward Carbon. Also, it is best if newspapers are shredded or at least torn up, and soaked or at least wetted, before being put in the bin. Otherwise they will take very long to decompose and may even cool down your compost pile.
Can you put old compost in a compost bin?
Yes. Compost is one of the best ‘ingredients’ for a compost bin as long as it is not poor-quality. Not only that, but good-quality old compost is an excellent ’starter,’ be it when starting an As-You-Go pile or preparing a compost tumbler’s Batch. Finally, if you ever discover that your compost bin’s C:N ratio has tipped over a little too much in favour of either Carbon or Nitrogen, apart from taking other necessary measures, one of the best ways to get things back on track is to add high-quality old compost.
Should you place it in the sun or shade?
As a general rule, in the sun, but in practice it depends on a couple of factors.
Direct sun and the resultant heat speed up the process of decomposition, and they aid in ‘cooking’ the pile so this major benefit is a compelling reason for siting your bin in the sun.
Except that direct sun and high heat also dry a compost pile – which, you may recall from section How to use a compost bin – Wetness, needs to be damp. Thus, direct sun and high heat also eventually retard the process of decomposing by drying out the pile! You can put your bin in the sun and easily work around this drawback by monitoring the pile for dryness and watering it regularly.
On the other hand, if you are specifically doing vermicomposting, then you will need to avoid hot sun and keep your compost bin in mostly shade because typically worms cannot tolerate high heat.
Like many things in life, opt for a happy medium and try to locate your compost bin where it gets a good amount of sun in the morning and late afternoon but not the hot midday sun.
For more composting guidance see also: how to make a home compost heap.