Wood ash can be a great addition to your garden. In the gardening world you may be familiar with potash (derived from the term 'pot ash'), potash is the water soluble part of ash formed by burning plant material. Essentially it is a form of potassium, a vital nutrient for regulating a plants water balance and creating sugars and starches. Without enough potassium vegetables become more vulnerable to pests, diseases and drought.
Although potash is essential for raising healthy plants, too much of a good thing does not always result in success so you need to think about how you use it.
In the compost
Boost the fertility of your compost with a sprinkling of ash every so often. Ash is alkaline so use it sparingly or it may affect your worms and bacteria if the pH is raised too high.
Due to ashes alkalinity it it possible to use it as a substitute for liming. Just be cautious as ash alcalinity can vary considerably dependant on the type of wood being burnt and any other plant tissue that may be present as is the case when burning a bonfire. Generally speaking hardwood produces more ash and a higher concentration of nutrients than their softwood counterparts.
Before adding ash to your soil it is advisable to test your soil pH and potassium levels to make sure it will help, not hinder your soil and plants.
Direct to soil
Sprinkling ash onto soil may help to deter slugs and snails, sadly the effects vanish once the ash gets wet. It has also been reported that sprinkling ash when sowing carrots and dusting it on turnips can help ward off carrot and turnip flies. Root vegetables such as carrots, parsnips as well as fruit bushes and peas and beans all appreciate potash.
Where not to use ash
Being alkaline, wood ash should not be applied to soil that has a pH of 7.5 or greater, nor should it be used near acid loving plants such as blueberries. It may also encourage the fungus potato scab so avoid using it near where potatoes will be grown.
In summary, keep ash dry before use, test your soil before applying ash and make sure it is suitable for the plants you are applying it near.