Hydrangeas top the list of favorites for many gardeners with their large, showy blossoms and energetic growth. Lacecap and mophead hydrangeas give gardeners an opportunity to control the color of the blossoms. Because hydrangeas are sensitive to the pH levels in soil, their blossoms may change color if soil pH changes. To keep hydrangea blossoms pink, the soil pH level must be at least 6.0. This pH level will keep the hydrangea plant from absorbing aluminum in the soil, which turns the flowers blue.
Measure between 12 and 15 tbsp. of limestone for every 10 square feet of soil area. Sprinkle this amount of limestone carefully and evenly over the soil.
Scratch the limestone into the soil lightly with the hand rake to incorporate it into the soil.
Water the soil thoroughly so it can readily absorb the limestone.
Repeat the limestone treatment two to three times each growing season to keep the pH level above 6.0.
Fertilize the limestone by mixing liquid fertilizer with water according to package recommendations for the size of the hydrangea shrubs. Add the fertilizer to the soil around the hydrangeas, taking care not to splash it onto the plant's foliage to avoid burning the leaves and stems. Fertilize the hydrangeas in early spring and early or midsummer.