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Expert advice: Finding the “perfect balance” for your compost heap

01st March 2021

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Compost is crucial in every garden, whether you use traditional or no dig techniques. This extract from Nicky Scott’s newly released book ‘How to Make and Use Compost’ offers some valuable advice on one of the garden’s most important tasks.

Gather your materials
You can build a compost heap or fill a compost bin in one go. It’s a most satisfying process – if you can gather together enough of the right materials. For this exercise it’s best to avoid cooked food waste, and meat, fish or dairy.

- Dry, woody materials. Stockpile wood chippings/shreddings, cardboard, dry plant stems, hay, straw, dry leaves, etc.

- Anything that is fresh and green – if you wait until the spring when every- thing is growing, you can easily find places to cut nettles (which are excellent in the compost heap) and other weeds, as well as grass cuttings.

- All your peelings, etc. from the kitchen; there won’t be much of this, which is why it’s important to gather nettles and other fresh green sappy growth.

- Any fresh manures you can get to bulk up the heap.

- Garden lime and or wood ash – especially if you have a lot of acidic fruit or coniferous material to compost. Apply only as a thin dusting layer.

Some materials are more or less a perfect balance of browns and greens; for instance, fully unfurled bracken has plenty of wet sappy green growth balanced by the tougher structural stems, and so in theory a pile of bracken can be com- posted on its own. Pea and bean haulms also have just about the perfect balance of browns and greens – dry fibre to lush sappy material (see Carbon-to-nitrogen ratio and Bracken in the A–Z Guide).

Generally speaking, the more you mix up your material types the better; you cannot necessarily take one ‘brown’ material and mix it with one ‘green’ material and end up with perfect compost. Think about what you will need to mix in to add air and absorb moisture. Try to avoid too much of one thing – so, for example, if you prepare masses of squeezed citrus fruit you have a very particular situation to deal with, and will need to think about what will balance not only the nitrogen but also the acidity (see A–Z Guide).

Some individual substances take longer to break down than others, e.g. avocado skins and orange skins, but a few orange skins within a much larger mix of materials are not going to be very significant. I find avocado skins regularly in my finished compost, but they soon break down and disappear when I add that com- post to the soil. For more information about specific materials see the A–Z Guide.

Build your heap / fill your bin
It’s simple: all you need to do is to create alternating layers of browns and greens. Creating layers is an easy way to mix the two types of material together.

You don’t have to do this – you could mix up the materials in a tumbler or on the ground before piling them into your bin – but layering is probably the easiest way. Just how thick you make each layer very much depends on how wet and dense that material is. For example, fresh lush grass needs to be layered or mixed into the heap as soon as possible with absorbent and/or structural materials. If you leave it to compact and go sludgy and smelly it’s a very difficult job to get it aerobically composting.

Get the mix right

Too dry?

- If the materials seem too dry you can water the heap – rainwater is best; use a watering can, with a rose or a hose to spread the water evenly. As long as you have plenty of tough, structural materials, which allow excess water to drain away, it’s difficult to add too much water.

- The moisture content of a compost heap should be around 50 per cent, but without a moisture meter it’s difficult to gauge. However, you start to get a feel for when it’s too dry.

- One way to test the dryness of the heap is to take a small amount out, weigh it, pop it into a warm oven overnight and then reweigh it. If it is bone dry and has lost half its weight then you know your heap is half water, which is how it should be. Alternatively, you can just pick up a handful and squeeze – you should only be able to squeeze out a drop or two.

Caution: Do not turn heaps that are musty and dry – give them a thorough soaking first, otherwise you will be releasing all kinds of ‘bio-aerosols’ such as fungal spores, some of which are not a good idea to inhale (especially Aspergillus fumigatus, which can lead to the condition known as farmer’s lung).

Too wet?

It’s most common for compost heaps to be too wet, especially when lots of fresh vegetable peelings, or grass cuttings, etc., are being dumped. These heaps can smell and attract flies if you’re not careful. It’s best to avoid this situation by always adding structural and absorbent materials to your heap as you go along, rather than trying to rectify the problem afterwards.

- Instead of dumping waste with a high moisture content, mix it with some absorbent or structural materials first, or spread it out in a thin layer to cover the whole surface and then cover this layer with other material. If fruit flies become a problem then you can cover with finished compost, or even with a thin layer of soil.

- If you have serious amounts of citrus fruit, then a sprinkling of garden lime will help too, but the best plan is to mix it with absorbent and structural materials and get it composting as soon as possible.

- Fresh, wet material from the kitchen is high in nitrogen and will quickly become putrescent, so empty your kitchen caddy frequently. Don’t leave it to go anaerobic, smelly and attracting flies in your kitchen, especially when the weather is warm – try to empty it daily or at least twice a week. It’s more difficult to compost materials once they have started decomposing anaerobically.

- Large amounts of dense, wet material must be opened up as soon as possible with some harder structural materials (such as twigs, tough dry stalks or woodchippings) to allow the air through.

- Cardboard and scrunched-up paper will absorb liquid and add some structure in the short term.

Reproduced by kind permission of Green Books
“How to Make and Use Compost” by Nicky Scott
ISBN: 9780857845450
Available from all good bookstores or at


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