7 ways to use up and recycle firewood ashes


If you’re never sure what to do with the ash from your fireplace, don’t be too quick to dump it, give these helpful tips a try instead.

Every time you light a fire, you create a certain amount of ash. Dry wood is far more efficient and the sign of a good fire will be minimal ash in left afterwards. Many gardeners then use it to “sweeten” soil, in place of limestone, but if you plan to do this, you need to be careful.

Wood ash contains no nitrogen (this is burned off during a fire), but it does have other useful soil benefits, which vary depending on the wood used; calcium oxide levels will be about 30%, potassium can vary from 5-15%, potash 5-6%, phosphoric acid 1-2% but the number that is most critical is its pH – it can vary from 8-12, making it incredibly alkaline and a very strong amendment for soil. It also tends to be very water soluble, which can cause salts to build up in soils.

Before you spread any ashes in your garden, make sure your soil actually needs amending – check its pH, so you’re not over-doing the alkaline factor. Never use wood ashes around acid-loving plants like azaleas, camellias, rhododendrons and blueberries.

The best recommendation is to use 40-70g per square metre on a soil that needs it, and don’t use it at all if your soil is already alkaline. Dig it into soil about four weeks before you plan to plant anything.


1. Add it to your compost

Compost is naturally acidic so wood ash is a great addition, plus it adds calcium. Lightly sprinkle a layer of ash as you build up green and brown layers. Be careful to just sprinkle it though – too much will ruin it.

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2. Use it to de-ice instead of salt

Wood ash contains potash – potassium salts  which can be used to de-ice pathways in cold weather, although watch the run-off.

3. Fight algae

One tablespoon of wood ash for every 4000 litres of water in a pond full of algae can help aquatic plants compete with it.

4. Feed your tomatoes

Tomatoes love calcium. US organic gardening author and grower Mike McGrath places a quarter of a cup in the hole before he plants a tomato.

5. Use the ashes to clean

Is the glass front on your fireplace sooty? Dip a damp cloth into the ashes, then wipe the glass to get off stubborn soot.

6. Make soap

Wood ash was traditionally used to make lye, then mixed with animal fat and boiled to make soap. Use ash from hardwoods only.

7. Wood ash makes a great repellent for snails and slugs

So you don’t contaminate your soil, cut an old piece of garden hose or pipe in half lengthways, lay it around the edge of a raised bed, then fill with ash.



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NZ Life and Leisure This article first appeared in NZ Lifestyle Block Magazine.
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