Last updated on December 2nd, 2011
YOU CAN FIND, in your fireplace, a valuable soil amendment. Wood ashes are rich in Potash, the very substance that raises the pH of soil, and therefore “sweetens” it. Sweet soil is the delight of lilacs; I swear my own shrubs flower so well in May because of regular wood-ash applications made beneath them in fall, winter and early spring. If your lilacs produce too few flowers, Potash can be the panacea they require. And here are other plants that prefer sweet soil:
Clematis, Gypsophila, Iris (tall bearded hybrids only); Japanese anemones, Lilacs, Madonna Lily, Nasturtium, Passionflower, Peonies, Phlox, Sweet Peas, Virginia Creeper
Lavender, Rosemary, Thyme
Beets, Cauliflower, Cabbage, Leeks, Melons, Onions, Parsnips, Spinach
How much wood ash to use? This depends largely upon intuition. If you apply the ashes in fall, winter and early spring, as I do, you can hardly use too much; rain and snow dilute the concentration of Potash considerably. Here, I empty my thoroughly cooled fireplace ashes into a standard coal scuttle; when this is full, I pour the entire amount in a wide circle beneath the drip line of my mature lilac shrubs. For small ornamental, herb and vegetable plants, I pour about a cupful beneath drip lines.
For more definitive quantities, you must, of course, have your soil tested. Your county agent will leap at the chance to do this for you.
It is worth mentioning that Potash (and Lime, too) is a natural slug- and snail-deterrent. As I discovered last summer, these destructive mollusks abhor sweet earth.
Just take care when building a fire that you limit your burning material to hardwoods, and plain, not glossy, paper. Only these items are acceptable, after combustion, for garden use.
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