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My neighbor and I have a bet. He says fallen oak leaves make soil more acidic and I say that's not true. Can you settle this?


Actually, you are both right in a way. 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). Back a hundred years ago, a Danish chemist first developed the concept of pH (which means 'power of hydrogen'). Since then, it has been universally used in most fields of science. When oak leaves first fall off the trees, they have an acidic pH in the range of 4.5 to 5.5 depending on the type of oak tree they came from. If you were to mix them into the soil immediately, they would temporarily slightly acidify the surface layer of the soil, but as they quickly decompose, the soil would become more alkaline.

The net effect is that the oak leaves would not acidify the soil in the long run. Leaves are actually a good thing to work into your soil. As they decompose, they become food for the microorganisms that are essential for a healthy soil eco-system. They also help with minimizing soil compaction and keeping the soil structure loose. It is good practice to remove thick layers of leaves from your lawn to keep them from matting down and inhibiting the grass growth in the spring. Running your mower over the remaining leaves is really helpful to the organic matter content of the soil. I know some folks like to remove the leaves from their woodlands because they like the appearance, but keep in mind you are depriving the trees of their natural fertilizer.

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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.


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