Oak Leaf Mulch to Raise Soil pH

Oak Leaves are Acidic

• The pH of a freshly fallen oak leaf is between 3.2 and 3.8. That means that oak leaves are highly acidic. However, as they break down, their pH becomes much more neutral. Even incorporating high amounts of fresh oak leaves will not make a significant difference in the pH of soil.

Oak Leaves as Mulch

• Oak leaves make excellent mulch, but mulch does not have much affect on soil pH. A Michigan State University study from 1997 examined the effect of oak mulch on turf. It showed that after six years of applying oak leaves to the grass turf, the pH of the soil hovered around neutral and was actually slightly lower than the control plot.

Composting Oak Leaves

• Oak leaves are good for mulching, though they take a very long time to break down. Because oak leaves contain a high amount of lignin and a high proportion of carbon to nitrogen -- 60:1, in fact -- they decay very slowly. Shred oak leaves that you plan to compost and mix with green grass clippings to speed up the decay process.

Ways to Raise Soil pH

• Even though oak leaves cannot raise the pH of your soil, there are soil amendments that can. Most often gardeners use lime when soil pH is low. Lime is a combination of calcium carbonate and magnesium carbonate, along with other trace minerals. It should be applied according to the soil pH, but can take up to two years to completely modify soil pH.