Are ashes natural fertilizers for plants?

Yes, ashes are natural fertilizers for plants as long as they do not come from burning cardboard, painted or pressure-treated wood, or plywood or from grilling. Hardwood ashes contain three percent potassium and 15 percent calcium by weight. They may be used at one-half to twice as much as lime by weight to improve soil structure and tilth and to raise soils from acidic to neutral and alkaline ranges.