With winter now starting to bite the fire is getting put through it’s paces. This in turn creates lots of wood ash which can be put to very good use in the garden and compost – but you should know where to use as not all plants are a fan. Wood ash is an excellent source of lime and potassium for your garden. Not only that, using ashes in the garden also provides many of the trace elements that plants need to thrive. But wood ash does have a high pH, making it an alkaline substance, so should not be used around acid loving plants such as Camellias, Azaleas, Blueberries etc. If your garden contains a lot of acid loving plants only use the ash as part of your compost pile. Also not all wood ash is created equal. Ash from hardwoods like Oak contain higher levels of nutrients and minerals than those from soft woods like Pine.
Wood ash contains lots of potassium which 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. Like the potash content, the calcium carbonate content will also vary, so it’s a good idea to test the pH of your soil before adding the ash and three to six months after, you can do this by picking up a simple pH testing meter from the local garden centre. Being alkaline, wood ash obviously isn’t an ideal addition if your soil already has a pH of 7.5 or greater.
It’s also worth remembering that potash is extremely soluble, so keep it absolutely dry before you use it (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.
Wood ashes make a great addition to the compost heap, where they’ll aid fertility (most of the nutrients needed by plants are contained in them to some degree). If you have a lot, don’t add them all at once 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.
Sprinkling ash straight onto the soil also deters slugs and snails (the moment it gets wet, this effect unfortunately vanishes). I haven’t tried it myself, but some recommend sprinkling ash in the drills when you sow carrots, and dusting it on turnips to keep carrot and turnip fly away.
I generally add ash to the soil in spring and autumn, but 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.