Adjusting soil pH

Perennials

Class 1: Some Perennials Basics
Class 2: Garden Design
Class 3: Putting Pencil to Paper
Class 4: Soil Preparation and Planting
Class 5: Maintaining your Perennial Gardens
Class 6: Troubleshooting

Most common perennials prefer a soil pH of between 6.0 and 7.0. If your soil test results indicate the pH of your new bed is higher than 7.0 or lower than 6.0, certain plants will struggle. You’ll probably want to add materials to bring the pH to the proper level. (Note that there are acid-loving plants, such as blueberries and azalea, that require a soil pH below 6.0, but these are the exception rather than the rule.)

Lime (powdered limestone) is used to raise pH, or "sweeten" an acid soil. The amount of lime necessary depends on your soil type; heavy clay soil requires more lime to raise pH over a given area than sandy soil. Start by adding about 3 lbs. of lime per 100 sq. ft. if your soil is very sandy. Use about 10 lbs. per 100 sq. ft. if you have heavy clay. If your soil falls somewhere in between, use 5-8 lbs.

These are only approximations; you don’t need to weigh the bag or measure each section. Lime generally comes in 50 lb. bags. If you have sandy soil, use about half a bag per 1000 sq. ft. (for example, a 25' x 40' garden). For clay soil, spread two 50 lb. bags over that same area.

If your soil pH is higher than 7.0, you have alkaline soil, which you can acidify by adding sulfur. Use 1 lb. sulfur per 100 sq. ft. for sandy soil, 2 lbs. per 100 sq. ft. for clay soils.

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Garden Calculators

Visit the NGA Web site's Garden Calculators for more detailed information on changing your soil's pH.

How much limestone do you need?

How much sulfur do you need?