Wood Ash in the Garden

More and more of us are turning to wood burning to keep warm.  If we don’t mix the burnt ashes with coal, there’s no reason why we can’t add them to the garden or compost heap. 

Wood ash is a great addition to the garden as it contains potassium or potash.

Just as it does in humans, potassium regulates plants’ water balance (so tissue is firm and juicy), and has a part in transporting food within the plant and creating sugars and starches. Without enough, vegetables are more vulnerable to drought, frost, pests and diseases. So adding this to the garden is a great way to keep a balanced soil

Ash in the Compost Heap

Wood ashes make a great addition to the compost heap. If you have a lot add gradually over time as they are alkaline and raising the pH too much will affect the bacteria and worms at work. It’s better to keep the ash in a nearby container and sprinkle on a layer every so often.

If you tend to compost a lot of acidic material, such as fruit waste, the ashes will help to keep the compost at a lower pH and reduce the need to lime the vegetable plots at a later date. It could also help to dry the heap and keep the pesky fruit flies at bay.

Wood Ash as a Substitute for Lime

It is possible to substitute for the usual ground limestone. However, home-produced ash isn’t a standardized product, which means its content will vary, but I’d find that an enjoyable challenge. Hardwoods, for example, generally produce more ash and contain more nutrients than softwood. Bonfire ash is even more variable, because of the mix of plant tissue.

Like the potash content, the calcium carbonate content will also vary (although it’s unlikely to contain more than half that of ground limestone), so it’s a good idea to test the pH of your soil before adding the ash and three to six months after, to check on its effect. It wouldn’t hurt to check up on the potassium content while you’re at it. There’s no point in adding potash to a soil that’s already high in potassium, as too much can affect the plants’ take-up of other nutrients.

Where Not to Use Wood Ash in the Garden

Being alkaline, wood ash obviously isn’t an ideal addition if your soil already has a pH of 7.5 or greater. There’s no point in spreading it around acid-loving plants such as blueberries or hydrangeas. Nor is it recommended for areas where you intend to grow potatoes (much though they enjoy potassium) as increased alkalinity can encourage the fungus, potato scab.

It’s also worth remembering that potash is extremely soluble, so keeping it dry before use is advised (this includes before adding it to the compost heap). Leave your ashes out in the rain and all the potash will wash out and you’ll be left with a sticky and fairly useless sludge. If you pile a large amount of ash in one area, you also risk over-liming that area and damaging nearby plants.

Adding Ash Direct to the Soil

Sprinkling ash straight onto the soil could deters slugs and snail, until it gets wet though, then its effectiveness wears off. Some also claim sprinkling ash in the drills when you sow carrots, and dusting it on turnips to keep carrot and turnip fly away.

Spring and autumn are said to be the best time to spread the ash around but as we accumulate most of it in the winter I think it can be spread it around at other times whenever it’s available and you might as well if you know you can’t keep it bone-dry. Root vegetables such as carrots, parsnips, peas and beans (pods are a better weight and colour) and fruit all appreciate potash.

Fruit

 If you have only a little potash, it should go to dessert apples, redcurrants and gooseberries first, then to cooking apples, pears, raspberries, blackberries and strawberries. Plums, apricots, cherries and blackcurrants appreciate a regular sprinkle, but don’t need it so much.