You can compost some types of ash – but it’s best to avoid composting others.
You can compost:
- Ashes from untreated and unpainted wood fires
- Ashes from burning paper or cardboard
- Ashes from burning grasses (such as straw)
These ashes are fine in small amounts – but be careful as it can very quickly made the heap to alkaline. (This might be desirable for balancing out acidic compost heaps or acid soils but in most circumstances, it’s better to keep it neutral overall.) Mix it into the contents of the heap to avoid the small particles being blown around on the wind.
Make sure ashes are thoroughly cooled before adding them to your compost heap, otherwise dry materials in the compost may fire risk.
But don’t compost:
- Ash from fires that have included treated/painted wood
- Ash from fires that have included plastic or other synthetic materials
- Ashes from fires included upholstered furniture (such as sofas) or mixed household waste
- Ash from coal fires or peat fires
- Ashes leftover in a charcoal barbecue
- Ashes from fires that have been fuelled by commercials firelighters, lighter fluid or any type of petrol
- Ash from cigarettes or cigars
All these types of ash contain materials that are harmful to plants or animals, or in some cases, the wider ecosystem.
If in doubt and especially if you’re using your compost for growing edibles, leave it out.