Compost materials: Featured Img

What can you compost?

If you’re just starting to get into composting, chances are you’re wondering what you can compost. 

Here’s a quick answer – if it’s been recently alive, you can probably compost it. 

In fact, we’re surrounded by materials. You’ll find materials in your garden, home or office. If you run out of materials there, a trip to the countryside or the beach will yield even more materials. 

That’s not to say you should compost everything. You can compost most organic materials with the right conditions – but very often we don’t have the right conditions.

In this post we’ll cover some common materials you can use, as well as both some more unusual materials – and items you want to avoid. 

Compost Material

Carbon: Nitrogen ratio

The bacteria in your compost heap need nutrients to digest compost material and breed. Two of the main ones to think about are carbon and nitrogen.  

Compost materials that are high in nitrogen are called greens – even if they are brown. For example, manure is a green because it is high in nitrogen. Materials that are high in carbon are called browns. See our guide to C:N ratio for an in-depth guide and a guide to the C:N ratio for some common composting materials.

While you can overthink the exact mixture of greens and browns in your heap, it is good to ensure you have a roughly even mixture of both browns and greens. 

Material composition

It’s not just the C:N ratio that affects how well bacteria perform. Bacteria easily digest simple foods such as carbohydrates and sugar. That makes food waste an ideal option.

On the other hand, they find it harder to digest tough, woody material, which takes longer in the compost heap.   

Material size

The smaller the material, the hotter your pile will get and the faster it will decompose. This is especially important for the woody material mentioned above. 

Moisture level

If a compost heap is composed of materials high in moisture, it can take longer to decompose. That’s because the water in the compost stops oxygen from getting to bacteria. It’s a good idea to balance materials high in water with drier material, such as paper. 

From the garden

Compost materials from the garden.

Grass clippings

The combination of a nitrogen high green and the small size of cut grass means it gets hot fast. On its own, though, the high moisture content means it tends to go into a sticky mess.

Grass is best mixed with a brown to achieve a better carbon:nitrogen ratio and to soak up some of that moisture. 

Weeds and excess plants

Weeds pulled from your soil often make a great material for the compost pile, as they come with a bit of carbon rich soil that balances out the nitrogen. 

Most weeds won’t regrow after being composted – even if hot temperatures don’t kill then, the lack of light will. However, weed seeds, if not composted at a high temperature, are likely to survive, so it may be worth removing these. 

Woody plants

Sticks and woody plants are harder for compost bacteria to digest, and can take longer to compost. They do have their uses, though. Sticks placed at the bottom of the compost pile creates air spaces which help provide oxygen to bacteria. Smaller pieces of wood, especially when dry, can help create air spaces inside the compost heap. 

Woody plants, sticks and the like can be composted more quickly when broken up. If you have large quantities of woody material, it may be worth investing in a compost shredder or chipper. 

Larger pieces of wood can also be composted under the soil in a system known as Hugelkutur

Leaves

Leaves can be gathered and composted on their own – leaf mold makes fantastic compost. At full size, this can take a couple of years, so again they may be worth shredding. 

Leaves can be shredded with a lawnmower. When combined with grass they can make a fantastic composting material, with the carbon from the leaves offsetting the nitrogen from the grass. 

Green Manure

Green manure is plant material that is grown to enrich the soil. Different green manures achieve different things. For example, legumes will fix nitrogen from the air while alfalfa will draw minerals up from deep in the soil. 

Traditionally green manure is dug into the soil, but an alternative is to cut it and compost it. In the summer, unless you have a large garden, you may wish to save the space, but some green manure can be grown over winter. 

Note: In the UK I have found greenmanure.co.uk to be excellent for everything from information to delivery speed to quality. I last bought their field beans as green manure, but they grew so well and healthily I ended up leaving half till to harvest time and then eating both the young leaves and the beans. 

From the home, kitchen and office

Mixed waste in the compost heap.
Image by herb007

Vegetable and fruit scraps

Vegetables are full of carbohydrates, while fruit is full of sugar. Both are easily broken down by the bacteria in your compost. 

While lemon and orange peels are more acidic than many other compost materials, your compost heap is perfectly capable of handling a few peels. Banana peels make a great compost material, as they are high in potassium, which is one of the nutrients compost bacteria need. 

Coffee 

Both coffee grounds and coffee beans are high in nitrogen and decompose rapidly. I used to collect these from my office in pre-covid times and put them in my HotBin, and you can also collect them from your local cafe. Disposable coffee filters will also break down, and the extra carbon will help balance the ‘green’ coffee. 

Tea bags

Tea is a fantastic compost material. High in nitrogen, it can safely be added straight to the ground as well as to the compost heap. Do be aware that some teabags may contain small amounts of plastic. See our guide to composting tea bags for more information.   

Newspaper and cardboard

Shredded newspaper is a great source of carbon and is relatively easily digested – worms seem to love it. It is advisable to shred it, though, and a whole newspaper may resist digestion. 

Ripped and scrunched up cardboard also works well, and creates air space in the compost heap which helps speed up the compost heap without having to turn it to aerate it. Again, thick cardboard takes longer to compost, and you may find that cardboard on the edges of the heap takes a long time to compost. You can use this to your advantage by using the cardboard as a wrap around the exterior of the heap to provide insulation and warmth.  

You will find some sites not advising you to compost newspapers or cardboard because of ink. In the UK at least, regulations on ink are now so strict that polluting elements have been stripped out of the ink, and it shouldn’t be a threat to your compost or your plants. 

Shredded paper

I personally collect bags of shredded paper from the office to use in my compost heap. In addition to being a great ‘brown’ addition to the compost pile, it is also great way to absorb excess moisture. Don’t add too much, though, as it can lead to the compost pile getting too dry. 

Wood ash

Wood ash, whether from your fire place or from your garden fires, can be a great amendment to your compost heap, as it is high in minerals, calcium and potash, and may improve the quality of your compost.

Some books recommend being careful with the amounts you add as it can change the PH of your compost heap, so it might be best not to add huge amounts. 

I personally rarely add wood ash, as I tend to place my ash in a circle around tender young plants to protect them from slugs. 

From the countryside and the beach

Seaweed lying on beach.

Seaweed is a fantastic addition for the soil – and it doesn’t even need to be composted. Although it doesn’t contain much nitrogen, it is high in minerals and even contains hormones that encourage plant growth. See our section on seaweed in What to Compost in Winter for more information. 

Ponds and streams can be a good source of nitrogen weeds as well, but be careful only to remove detached or excess growth. A walk in the forest (or many city streets) can yield large quantities of leaves in the autumn and winter. I even know one intrepid composter who keeps a sack and shovel in the boot for collecting animal dung in the countryside, 

Manure (from herbivores)

Manure on a blue tarpaulin before being added to compost.

Manure is a superb compost material. In fact, the Rodale Book of Compost advises it should be the first item on your list. I often find that the addition of a small amount of chicken manure rapidly causes my compost to heat up. All manure from plant-eating animals is good for compost. 

However, one word of warning. Many animals are now fed on hay which contains herbicides. Read my tale of woe with manure before taking any risk. 

Learn more about using manure.

Unusual materials

Egg/oyster/claim/crab shells

Shells are an excellent provider of calcium. They can take a long time to break down, and so it is best to crush them well before adding. 

Hair, both human and pet

This compost material is very high in nitrogen. In fact, 6-7 pounds of hair can contain as much nitrogen as 100-200 pounds of manure. It is easily available from your hairdresser, although mine did give me a very strange look when I requested a bag. 

Urine

Urine is very high in nitrogen. It can help to activate compost and balance compost which is high in brown compost material. 

Out of date wine and beer

Some composters believe the yeast in these helps the compost process, especially if combined with the ammonia in urine.  

Old potting soil

A bit of soil can help balance out very green piles. I try not to add too much, though, as it’s not going to add new nutrients to the finished compost. 

Blood meal

Experiments at the Rodale Research Centre added blood meal to compost at rates of 3 pounds blood meal to every 31 pounds of compost material. It resulted in a significant increase in compost activity. 

Materials to be careful with

Most organic things can be composted with a combination of the right conditions and enough time. But those conditions can be hard to replicate in the garden. Large items need to be ground up, while other items food needs to be buried in the compost heap and composted at a high temperature. 

So while the items below can be composted, they are for the serious composter who has the right tools and conditions for the job. 

  • Meat, dairy, cooked food: Can attract rats.
  • Fish: Great for soil, but very smelly, attracts pests. 
  • Bones: Can be composted (even human bodies can be composted) but if not treated right take a seriously long time
  • Grease, oil, fact: Can block up spaces for air in the compost heap. Can be pre-composted in a Bokashi bin
  • Charcoal ash: Can contain a binding chemical harmful to your soil, and should be avoided unless you are confident chemicals have not been added. 
  • Weed seeds: Should be avoided unless you can be sure of high temperatures in your compost. 
  • Manure from carnivores: Dog and cat manure can carry pathogens, and should only be composted if you are sure you can achieve thermophilic temperatures. 
  • Lime: Some composters add lime to their compost in order to adjust the PH. However, compost tends to end up with a stable PH even if acidic or alkaline at the start of the process. The Rodale Book of Compost also warns that adding lime can be harmful to the compost process if you are composting manure. 

The materials listed here are not an exhaustive list!

Remember, most things which have recently been alive can be composted, but it’s worth taking care with what you compost unless you have very hot temperatures.