How do fireplace ashes affect lawn growth? Do they fertilize or change the pH in a favorable way? Or are they harmful? Charlie
Answer
Thank you for a great question. Let me begin my answer by setting the stage with an explanation of pH which I've written about previously. Acidity is measured by a term called pH which is represented by a number scale from 0 to 14. A pH of 7 is neutral; pH below 7 is acidic and pH above 7 is basic (or alkaline). Wood ash contains lots of micronutrients which are good for the soil, but also lots of calcium. Calcium causes the wood ash from fireplaces and stoves to be highly alkaline with pH 9 and above, depending on the type of wood burned. High alkalinity is not necessarily bad, but you must be very careful before spreading wood ash on your lawn.
The significant majority of our soils in this region are acidic (low pH) which is why lime (which has a high pH) is added to adjust them closer to neutral (a pH of 6.5-6.8 is best for grass). But, (and it's a big "but"), lime (or anything else like wood ash that is alkaline) should only be applied to your lawn after a soil test has been done to confirm that the soil has a low pH and the amount of pH adjustment required. If you apply lime or spread wood ash without doing a soil test first, you are running the real risk of making your soil too alkaline, which could damage or kill your lawn. I recommend an annual soil test to monitor your lawn's chemistry. If your soil test calls for "X" lbs of lime per 1000ft2, somewhat more wood ash will be needed. I recommend going cautiously however and only spread the same amount of wood ash as you would lime and follow-up again next year with another soil test. That way, you can't overcorrect the pH. If you need your soil tested, call us, we do it all the time.
Wood ash does not provide any fertilizer value, because it contains virtually no nitrogen. Wood ash does however; contain potassium which is a good thing because it helps promote root growth in plants. Caution- If you are tempted to spread wood ash around the base of your plants and shrubs, make sure that you do not spread it around acid-loving plants. Many of our popular plants in this area are acid-loving and wood ash would be a very detrimental. Keep wood ash away from: blueberries, azaleas, rhododendrons, and mountain laurel to name a few.
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About Linda Lillie
Linda K. Lillie is the President of Sprigs & Twigs, Inc, the premier
landscape design and maintenance, tree care, lawn care, stonework, and carpentry
service provider in southeastern Connecticut since 1997. She is a graduate of
Connecticut College in Botany, a Connecticut Master Gardener and a national
award winning landscape designer for her landscape design and landscape installation work.
