Ash contains mainly calcium, potassium and magnesium. It's very similar to lime, more effective actually since its particles are finer. If you have pine trees dropping their acidic needles on your garden, which is common in places like New Hampshire, ash is a great way to reduce the acidity of the soil. I spread a little all over my garden in the spring, and maybe a little more throughout the summer. I also spread it on my lawn, as grass likes a basic soil so the ash will ensure that the acidity of the soil remains low. Certain plants, like blueberries, cranberries, rhododendrons and azaleas, actually like acidic soil, so you have to be sure to avoid ashing these if you have any in your garden. I put all my ash in a trash can outside and in the spring, spread it all over my yard, even if there's still snow on it. When everything melts and the water travels into the soil, the nutrients of the ash is deposited. If you till your garden then you can just throw it on right before that. You don't want to keep dumping every clean out in one area regardless of what's growing there, unless you don't care about what's growing there.