Compost for Beginners: What to Add and What to Avoid

A compost heap turns kitchen scraps and garden waste into dark, crumbly material you can spread on beds and around plants. It does not need special equipment to start, and it does not need to be perfect. What it does need is a workable mix of materials, enough air, and a little patience while microbes do the breaking down.

Most beginners fail for one of two reasons: the heap is too wet and airless, or it is made almost entirely from one kind of material. Both problems are easy to fix once you know what to look for. This guide explains what to add, what to leave out, how to balance the heap, and how long the process typically takes.

Start with a simple heap

Choose a spot that is level, well drained, and easy to reach with a wheelbarrow. A heap that is hard to reach will not get turned or added to, so convenience matters more than a perfect location. Partial shade is helpful because it stops the heap drying out too quickly in summer, but a sunny spot will still work if you water it occasionally.

A heap about 1 metre wide, 1 metre deep, and 1 metre high is a practical size for most gardens. Smaller heaps break down more slowly because they lose heat, while much larger heaps are hard to turn by hand. You can build a heap in an open pile, in a simple bin made from pallets, or in a bought compost bin. The container matters less than the mix inside it.

Start with a layer of coarse material, such as small twigs or straw, about 10 centimetres deep. This helps air move underneath the heap. Then add materials in layers rather than dumping one large load of a single thing on top. A common guideline is to aim for roughly two or three parts brown material to one part green material by volume. You do not need to measure this precisely; a rough balance, checked by eye, is enough for a home heap.

If you are also learning about your soil, it helps to read how to test soil pH before you spread finished compost widely. Compost generally supports soil life, but knowing whether your soil is acidic or alkaline helps you decide where to use it first.

What to add: greens and browns

Green materials are soft, moist, and rich in nitrogen. They include vegetable peelings, fruit scraps, coffee grounds, tea leaves, fresh grass clippings, and young weeds that have not set seed. Browns are dry, carbon-rich materials. They include shredded cardboard, dry leaves, straw, wood chip, sawdust from untreated wood, and torn newspaper in small amounts.

Both groups are needed. Greens feed the microbes that break material down, while browns provide structure and air spaces and help prevent a soggy, smelly heap. A heap made only of grass clippings, for example, quickly becomes a dense, wet mat. A heap made only of dry leaves breaks down very slowly. Mixing the two keeps the process moving.

Chop or shred larger items before adding them. Vegetable stalks, cardboard, and woody prunings break down much faster when they are cut into pieces smaller than about 5 centimetres. This step takes a few minutes, but it can shorten the overall time by weeks.

A useful habit is to keep a small covered bucket in the kitchen for scraps and a separate pile of browns beside the heap. That way, every time you add greens, you can cover them straight away with a handful of browns. Covering fresh food scraps also helps reduce flies.

What to leave out

Some materials cause smells, attract rats, or introduce problems that are hard to remove later. Leave out meat, fish, dairy products, fats, and cooked food in an open heap. These break down slowly, smell strongly, and attract pests. A sealed hot composting system can handle some of these, but a standard home heap should not.

Also leave out diseased plants, weeds with ripe seeds, and perennial weed roots such as bindweed. Home heaps typically do not get hot enough to kill all seeds and disease organisms, so those materials can come back when you spread the compost. Woody material thicker than a finger should be chipped first or set aside; large branches will still be recognisable long after the rest of the heap has rotted down.

Avoid glossy or heavily printed paper, treated timber, sawdust from treated wood, and ash from coal. Wood ash from a fire in small amounts is sometimes used, but it is alkaline and easy to overdo, so it is safer for beginners to leave it out. If you use any garden product on plants before composting them, follow the product label and check whether the material is suitable for composting.

Cat and dog waste should not go in a heap that will be used on food-growing beds. The same applies to nappies and other hygiene waste. When in doubt, leave the item out. A slightly smaller heap is always better than one that causes a problem later.

Keeping the heap working

A working heap should feel damp, like a wrung-out sponge. If you squeeze a handful and water drips out freely, it is too wet. Add dry browns and turn it to let air in. If it feels dry and dusty, sprinkle it with water while you turn it. In dry weather, check the heap every two or three weeks.

Turning speeds up composting, but you do not need to turn it every day. Turning every four to six weeks is a common guideline for a home heap. Use a fork to move material from the outside to the centre, where it breaks down fastest. If turning a full heap is difficult, even loosening the top 30 centimetres and pushing a few air holes through with a fork or stick will help.

Temperature is a useful clue, but you do not need a thermometer. A heap that feels warm in the centre after a few days is working well. A heap that stays cold is usually too dry, too small, or short of greens. Add a bucket of fresh green material and some water, then cover it with browns and leave it for a week before checking again.

Finished compost is dark brown, crumbly, and smells earthy rather than sour. You should not be able to recognise most of the original ingredients, although a few woody pieces may remain. Those can be sieved out and returned to the next heap. In a well-balanced heap, this stage typically takes three to six months, although cold weather and coarse materials can extend it to nine months or more.

Using finished compost

Spread finished compost on beds at a depth of about 2 to 5 centimetres and work it lightly into the top few centimetres of soil, or leave it as a mulch. For containers, mix roughly one part compost to three parts potting mix by volume. Fresh compost is not a direct replacement for soil, and using it too thickly can smother small plants, so a moderate layer is best.

Compost is most useful when it is used where soil needs structure. Improving clay soil and improving sandy soil both benefit from regular additions, because compost helps clay drain better and helps sand hold moisture for longer. In both cases, a little compost applied often is more effective than a single very thick layer.

Common mistakes

• Adding only grass clippings, which mat together and turn slimy.
• Leaving food scraps uncovered, which attracts flies and rats.
• Letting the heap dry out completely in summer and then wondering why nothing has rotted.
• Adding diseased plants or seeding weeds and spreading the problem around the garden.
• Expecting finished compost in a few weeks from a small, unturned heap.
• Using compost that still smells sour or ammonia-like, which can harm seedlings.

Most of these mistakes are easy to correct. Add browns, cover fresh material, water in dry spells, and give the heap time. Compost making is forgiving, and a heap that looks untidy can still produce excellent material if the balance is roughly right.