Wood ash allowed to `age` for a few months and kept dry provides excellent fertilizer for the garden. Look in your Search Engine for further information, ie: `Wikipedia`
Re my answer, I was actually refering to fresh soot and not wood ash when I said to let age, but it`s still good advise, just keep it off the foliage as it may scorch.
I think what you are thinking of is: When my wood burning stove needs to be cleaned out, full of ash, I take it to my garden and spread it out. It does affect the acidity/alch (Ph) of the soil. Where I live I have to add lime every once in a while, thisash takes the place of lime. So when I need to add lime every spring, I don't use as much lime since I had been spreading ashes on the soil.