Wood ash is an excellent source of lime and potassium for your garden. Not only that, using ashes in the garden also provides many of the trace elements that plants need to thrive. But wood ash fertilizer is best used either lightly scattered or by first being composted along with the rest of your compost. This is because wood ash will produce lye and salts if it gets wet. In small quantities, the lye and salt will not cause problems, but in larger amounts, the lye and salt may burn your plants. Composting fireplace ashes allows the lye and salt to be leached away. Not all wood ash fertilizers are the same. If the fireplace ashes in your compost are made primarily from hardwoods, like oak and maple, the nutrients and minerals that will be in your wood ash will be much higher. If the fireplace ashes in your compost are made mostly by burning softwoods, like pine or firs, there will be less nutrients and minerals in the ash. Wood ash is also useful for pest control. The salt in the wood ash will kill bothersome pests like snails, slugs and some kinds of soft bodied invertebrates. To use wood ash for pest control, simply sprinkle it around the base of plants that are being attacked by soft bodied pests. If the ash gets wet, you will need to refresh the wood ashes as the water will leach away the salt that makes wood ashes an effective pest control. Another use for ashes in the garden is to change the pH of the soil. Wood ashes will raise the pH and lower the acid in soil. Because of this, you should also be careful not to use wood ashes as fertilizer on acid loving plants like azaleas, gardenias and blueberries.