Using wood ash in the garden – some do’s and don’ts

After a chilly couple of months, those of you with wood burners and open fires have probably got quite a lot of ash stored somewhere. So can you do something better with it than putting in land fill? Well, as wood ash contains Potassium and traces of Calcium and Magnessium, all key plant nutrients, the answer is yes you can! There are however a few things to consider; firstly our Warwickshire clay tends to be on the alkaline side of the ph scale and adding wood ash has the same effect as liming, that is to raise the ph of the soil and make it even more alkaline. So this is good (in moderation) for some vegetables (cabbages, sprouts etc) and fruit trees (apples, pears, cherries) and especially helpful if you have had club root problems with your brassicas. For fruit trees a light top dressing will encourage both leaf and fruit production, but don’t leave a big pile of ash as this can lead to a build up of salts which aren’t good for plants. Ash is not so good, in fact positively bad, for plants that like acid conditions like Camellias, Rhododendrons, Roses and Raspberries and you should never use it where potatoes are grown as the increased alkalinity encourages potatoes scab. You can add it to your compost bin but it needs to be mixed well with other material and so a thin sprinkling every 6″ of compost is o.k. Don’t use coal ash in either your compost or on the garden there are too many toxic heavy metals in coal ash, notably high concentrations of arsenic. You shouldn’t use ash from treated or varnished wood for the same reason. So, if you’ve got fruit trees or rhubarb or grow brassicas then save your money and don’t buy preparations like sulphate of potash or fruit fertilisers and recycle your wood ash.