There are plenty of good reasons to have a wood-burning fireplace. It can help cut your home heating costs in winter, it still works when the power goes out, and it’s just plain comforting to sit in front of a crackling fire on a cold evening.
If you’re a gardener, you have yet another reason to love your fireplace. Wood fires naturally create ash, and adding ash to your garden in moderation can be a cost-effective way to boost your plants’ growth. So, which plants like wood ash, and how can you use it?
Using Wood Ash as a Soil Amendment and Fertilizer
Wood ash isn’t as concentrated as commercial fertilizers, but it’s a good source of potassium (the second ingredient, after nitrogen, on fertilizer bags). Ash also contains useful quantities of calcium, phosphorus, and magnesium, as well as trace minerals such as boron, copper, molybdenum, and zinc.
Ash’s high calcium content means it’s useful as a soil amendment to help raise the soil’s pH. Before applying wood ash to your soil, conduct a basic soil test to determine whether it needs these nutrients. A good rule of thumb is 5 pounds of wood ash (roughly what you’ll get from a cord of wood) per 100 square feet of soil, applied once a year. For example, if you have a raised garden bed that measures 4 feet by 8 feet (totaling 32 square feet) you would need just over 1.5 pounds of wood ash to treat the soil.
But is wood ash good for plants? It depends. Calcium deficiency in your soil can cause blossom-end rot in tomatoes, and the ash may be a helpful remedy. It’s also useful if the soil is too acidic for your plants’ liking.
If you have acid-loving plants such as blueberries, rhododendrons, and holly, however, avoid using wood ash as fertilizer. Keep it away from potato patches, too, as wood ash can lead to scab, a soil-borne disease.
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Adding Wood Ash to Compost
Another way to use wood ash in the garden, without worrying about which plants will or won’t benefit from it, is to put it in your compost instead of applying it directly to the soil. It can be chucked into the pile along with grass clippings, sawdust, leaves, coffee grounds, vegetable scraps, crushed eggshells, and cardboard.
A working compost pile is mildly acidic, so moderate amounts of wood ash can help keep it balanced. Anything up to 5% of your pile by volume is fine. Beyond that, your compost may become too alkaline, which will slow its decomposition.
There are a few other caveats as well: Don’t use ash from painted, stained, or pressure-treated wood, or charcoal ash from your grill, which can contain toxic chemicals. Additionally, never add hot ashes to your compost pile as it can catch fire. Within those limitations, wood ash can genuinely help your garden thrive.
