If you’ve recently had a bonfire, or like to warm yourself in front of a roaring fireplace or wood burner, then you’ll probably have lots of ash. Getting rid of it can be a bit of a nuisance, but it’s also a valuable source of nutrients, which makes it a great resource for the garden.
Wood Ash Nutrients
Wood ash is naturally high in potassium, which encourages flowering and fruiting. It also contains phosphorous as well as a catalog of micronutrients including manganese, iron, zinc and calcium.
Younger wood, such as twiggy prunings, produces ash with a higher concentration of nutrients than older wood. Similarly, ash from hardwoods like oak, maple and beech contain more nutrients than ashes of softwoods.
Ash from lumpwood charcoal is also good, but avoid using the ash from coal or treated timber, which could harm your soil and plants.
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Wood ash can help make compost less acidic
Using Wood Ash in Compost
Wood ash is alkaline, so applying it to compost heaps helps to balance the tendency of compost to be more acidic. It also creates better conditions for composting worms, which will speed up decomposition. Compost that’s less acidic is perfect for mulching around vegetables.
Add wood ash little and often in thin layers. A few handfuls or one shovelful every six inches (15cm) of material is fine.
Using Wood Ash on Soil
Wood ash can play a useful role in correcting overly acidic soil. Most vegetables need a pH of 6.5 to 7.0, so if your soil’s below 6.5 sprinkle wood ash over the surface then rake or fork it in. Test your soil using an inexpensive test kit if you don’t already know its pH. Wood ash is particularly useful if you use lots of cattle manure in your garden, as this type of manure is very acidic.
Wood ash is approximately half as effective as lime in neutralising acid. As a general rule, apply about two ounces of ash to every square yard (50-70g per square meter). Do this on a still day in winter and wear gloves to protect your hands.
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Wood ash can be used around brassicas in place of lime
Using Wood Ash around Plants
Use the alkalinity of wood ash to improve soil for brassicas such as cabbage and Brussels sprouts. This is a great way to prevent club root, a common disease when soil’s too acidic. Apply it the winter before planting, or as a side dressing around actively growing plants.
Its high potassium content means wood ash is ideal to use around most fruit bushes, including currants and gooseberries, where it also helps wood to ripen, thereby improving hardiness, disease resistance and productivity. In fact, mix it into any soil used to grow fruiting vegetables, especially tomatoes.
Where Not to Use Wood Ash
Due to its alkalinity, wood ash shouldn’t be used around acid-loving plants such as blueberries and, to a lesser extent, raspberries. Don’t apply it to areas used to grow potatoes, as alkaline soil encourages potato scab. Avoid it coming into contact with seedlings too.
You’d need to add lots of wood ash to make your soil too alkaline for most crops. But for peace of mind re-test your soil’s pH every couple of years to check it doesn’t go above 7.5.
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Store wood ash in a container with a close-fitting lid until you're ready to use it
How to Store Wood Ash
Finally, a word on storing wood ash. Because the nutrients it contains are soluble, you’ll need to keep it out of the rain so they don’t wash out. Containers with close-fitting lids are perfect for keeping ash dry until you’re ready to use it.
Wood ash can be a truly useful addition to the garden. If you use it too, please share your experiences in the comments section below.
