Raising pH with Limestone

For acid soils, ground limestone is a good form of soil amendment to use because it is available to the plants over a long period of time, slowly dissolving over a period of years. Limestone does take a while to work—most often, we recommend that people apply lime in the fall so it’ll have achieved its work by the following spring. If you spread ground limestone in the fall on freshly worked soil, it will work its way through the soil over the winter in time for spring. Be sure to spread it evenly, as it does not spread but rather sinks into the soil.

The following chart shows the number of pounds of ground limestone (calcium carbonate) needed per 100 square feet to raise soil pH to 6.5. Till this amount into the soil as deeply as possible. Lime moves very slowly in soil. If it is just spread on the surface, it may take years for it to affect the soil a foot deep.

Soil with lots of clay, and soil with a high organic matter content, buffer the pH. This means it takes more lime to change the pH. In soils like these, or if your soil is extremely acid (lower than pH 5.0), it may take a few years of lime treatments to raise your pH to where you want it.

Pounds of Limestone Per 100 Square Feet

Current pH Sandy Loam Loam Clay Loam
4.0 11.5 16 23
4.5 9.5 13.5 19.5
5.0 8 10.5 15
5.5 6 8 10.5
6.0 3 4 5.5