Fireplace ash can be used as a substitute for lime in very acidic soils. It also provides many trace elements that plants need and the trees and fungi you are burning had already mined and stored.

You may want to keep a special ask bucket to make sure you only get pure wood in the loads that you plan to use. Store them in a metal trash can or similar and make sure that you are careful, it is very dangerous if improperly handled. One use for ashes is to make lye, and lye is extremely caustic so keep that in mind.

Fireplace ashes can be used whnever you have to acidic of a soil, SMALL amount to your compost pile can help, larger amounts can be used if you have to much (N) Nitrogen in your compost, N will make it heat up and fireplace ashes can cool it. In the same respect fireplace ashes can kill your compost if you use too much when it wasn’t needed. If you have to much “green” in your compost , add a bit of fireplace ash in the layers to help it even out.

Some other tips:

• Where long sleeves and proper clothing when applying wood ash. Use the same precautions you would use when handling bleach, as they are about equally dangerous. Wear eye protection and gloves. Depending on the fineness of the ash, you may want to wear a dust mask.
• Do not use ash from burning trash, cardboard, coal or pressure-treated, painted or stained wood. These substances contain toxic elements, harmful to plants when applied in excessive amounts. For example, the glue in cardboard boxes and paper bags contains boron, an element toxic to many plant species at levels slightly higher than that required for normal growth.
• Do not use ash on alkaline soils or on acid-loving plants.
• Do not apply wood ash to a potato patch as wood ashes may favor the development of potato scab, though in can be used in compost that will be used on potatoes..
• Do not apply ash to newly germinated seeds, or very young plants as ash contains too many salts for seedlings, though again it can be used if properly composted.
• Do not add ash with nitrogen fertilizers such as ammonium sulfate (21-0-0-24S), urea (46-0-0) or ammonium nitrate (34-0-0). These fertilizers produce ammonia gas when placed in contact with high pH materials such as wood ash.

  Use what you can here, and you may even want to try soap making in the future, good luck.