Is Wood Ash a Good Thing to Add to Your Compost? 

Yes ……..and No.

With the cooler weather, those of us with log burners are beginning to produce ash, and there is a question about how to use it in the garden.

Wood ash is a good source of potassium (potash), calcium carbonate (lime) and trace elements, but it does not contain much nitrogen. It makes a good addition to your compost heap in small doses. But, because the ash is alkaline, adding too much can negatively affect the decomposition of the compost. So, sprinkle a light coating over the compost and don’t add any more until you have added another layer of compostable material.

If you have more ash than the compost can handle, or you can wait, it might be better to collect the ash, store it somewhere dry, and only mix it with the compost when the compost is fully decomposed and ready to apply to the soil. Then mix it in thoroughly and dig in or apply the compost as a mulch. Don’t use it around acid-loving plants such as blueberries, Rhododendrons and Camellia.

You can add ash directly to the soil; it is best to add wood ash to the soil in spring and autumn, but it can be spread around at other times and if you have it available, you might as well. Vegetables such as carrots, parsnips, peas and beans and fruit all need higher levels of potassium.

There is some evidence that freshly applied ash acts as a deterrent to slugs and snails, but this effect quickly diminishes when the ash becomes wet.

Note: Do not use the wood ash in the compost or garden if materials other than wood, paper and organic material have been burnt in the fire. Test your soil pH before spreading large amounts around; don’t use it in areas where the pH is above 7.5.

See also How to Make the Best Compost

David Brittain
Kiwicare