Alkaline Fertilizer for Hydrangeas

Bloom Colors

• Although acid soils make aluminum available to the hydrangea and turn the flowers blue, growing hydrangeas in alkaline soil reduces the amount of aluminum available to the plant, resulting in pink flowers. Acidity, expressed as pH levels, ranges from 0.0 to 14.0, with 7.0 considered neutral. The higher the number, the more alkaline the soil is. To reduce acidity and help a hydrangea produce pink flowers, apply fertilizer products to raise the pH level.

Soil Testing

• Before you dump fertilizer on your hydrangea plants in hopes of turning the soil alkaline, take a soil test. Soil test kits are available from cooperative extension service offices and many garden centers. Soil analysis provides crucial information on a garden's current pH levels, as well as the level of a variety of nutrients important to plant growth and health. A basic pH soil test is often an inexpensive option that not only tells you the soil's current acidity level, but also how to raise or lower the pH.

Raising pH Levels

• Treat the soil around a hydrangea with lime if the soil test shows the soil is too acidic or neutral. Use 1/2 cup of dolomitic lime for every 10 square feet of soil area. Lime raises the acidity level, but the process can take up to a year and more than one application. Granular or water-soluble fertilizers that contain nitrate nitrogen help maintain or raise the pH level in garden soils. Follow package directions.

  For faster results, mix one tablespoon of hydrated lime with one gallon of water and pour it directly onto the ground at the base of the hydrangeas in March. Repeat the application in April and again in May. Water the mixture into the soil.

Tips

• Try spreading fireplace ashes around the base of the hydrangeas to help raise the pH level.
  Never spread any additive or fertilizer so close to the plant that it touches the main stem, and try to keep all fertilizers off the leaves. Water the hydrangea deeply immediately after applying granular fertilizers and additives such as lime and be sure to rinse off the foliage if any of the product has drifted during application.