What to put in your compost

The key thing to remember when adding materials to your compost is that you want a good balance between carbon rich and nitrogen rich ingredients. This is needed because the microorganisms which break down compost have quite a fine balance of carbon and nitrogen in their bodies, which must be maintained for them to remain active. This balance is often expressed as a C:N (carbon:nitrogen) ratio. Microorganisms have a C:N ratio of around 8:1. Straw, on the other hand, has a ratio of about 80:1. Therefore if you put predominantly straw on your compost heap the microorganisms will rapidly stop working due to a lack of nitrogen. The same applies if you put too much nitrogen rich material on the heap. You should roughly aim to put no more than twice as much carbon rich material on your heap as nitrogen rich material, or in equal quantities.

The material you add to your compost should be chopped or shredded as much as possible before it’s added to the heap to speed up the decomposition process. Make sure you add a good variety of materials.

Carbon rich materials you can add to your compost:

  • Cardboard
  • Woody prunings
  • Old plants (also called ‘haulm’)
  • Hedge clippings
  • Straw
  • Dead leaves
  • Paper
  • Wood chippings
  • Sawdust

Nitrogen rich materials you can add to your compost:

  • Grass clippings
  • Kitchen (plant based) waste
  • Seaweed
  • Ephemeral and annual weeds which have not set seed

Things you shouldn’t add to your compost:

  • Too much paper with ink on it.
  • Glossy paper.
  • Corrugated cardboard boxes (the glue used may contain high levels of boron which can become toxic to plants).
  • Any diseased plant material.
  • Perennial weeds (which may survive in the compost) or other weeds which have set seed.
  • Meat or cooked foods.