by Glennis Drew
According to Heather Rhoades of the website, Gardening Know How, the short answer is “Yes! (but only once the ashes have been allowed to cool completely in a metal container with a lid, on the ground, away from your house.)
Wood ashes are 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 ashes will produce lye and salts if it gets wet. In small quantities, the lye and salts will not cause problems, but in larger amounts, the lye and salts may burn your plants. Composting fireplace ashes allows the lye and salts to be leached away.
Not all wood ash fertilizers are the same. If the fireplace ashes in your compost are primarily from the burning of hardwoods, such as oak and maple, the nutrients and minerals in your wood ashes will be much higher. If the fireplace ashes in your compost are mostly from burning softwoods such as pine or firs, there will be fewer nutrients and minerals in the ashes.
Wood ashes are also useful for pest control. The salts in the wood ashes will kill bothersome pests such as snails, slugs and some kinds of soft-bodied invertebrates. To use wood ashes for pest control, simply sprinkle them around the base of plants being attacked by soft-bodied pests. If the ashes get wet, you’ll need to refresh the wood ashes because the water will leach away the salts 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 such as azaleas, gardenias and blueberries.”