Lime reduces acidity of soil. Many flowers, such as roses, prefer low acidity. If you are planting roses or other low-acid flowers you should test the soil first to determine the pH. The lower the pH value of soil, the more acidic it is. Adding garden lime will raise the pH to more optimal levels for plant growth. Lime is best used alone to do its job properly. Using other fertilizers (which may raise acidity) at the same time can cancel out lime’s effects.
Till the flower bed and take soil samples. If the soil is too acidic for the flowers you plan to plant, you should add lime before planting. You should do it in the fall, if possible, long before the spring planting--this gives it time to settle into the soil. You can buy a soil-testing kit or look for an extension office that provides soil testing. The extension office usually charges a fee, but the test will be pretty accurate. Most flowers can do well in a soil with pH ranging between 6.0 and 7.0.
Spread lime evenly over the soil surface. The amount of lime needed depends on your soil’s acidity and the soil type. For example, you should add approximately 4 lbs. of lime per 100 square feet if you have sandy soil, suggests the Washington State University Extension. You shouldn’t need more than this and you might need much less, and although the extension's estimate is for vegetable gardens, it applies to flowers as well.
Use a garden rake, a long trowel, or a pitchfork to work the lime down into the soil a couple of inches. If you are doing this in the fall, the lime will gradually seep further down over the winter.
Water the soil lightly. This keeps any lime remaining on the surface from blowing to one side of the flower bed or the other.