The University of Georgia College
of Agricultural & Environmental Sciences
Cooperative Extension Service

Growing Bigleaf Hydrangea

Gary L. Wade, Extension Horticulturist

Bigleaf hydrangea, Hydrangea macrophylla, also called French, Japanese or Snowball hydrangea, is both a florist plant and landscape plant in Georgia. Often purchased as a gift plant from florists, bigleaf hydrangea can be transplanted to the landscape for repeat blooms each year. Homeowners delight in changing the flower color from pink to blue or from blue to pink by adjusting the pH of their soil.

Location
Bigleaf hydrangea prefers morning sun, afternoon shade, and a moist, well-drained soil. Avoid planting it on hot, dry, exposed sites. Cold damage to the buds may occur in winter and late spring, so be prepared to provide some winter protection by covering the plant with an old sheet, blanket or cardboard container when temperatures drop below freezing. A cylinder of chicken wire placed around the plant and filled with leaves also provides excellent cold protection.

Bigleaf hydrangea can easily be grown in containers and is an excellent patio plant. Another advantage of growing the plant in a container is that it can be moved indoors on a cold night.

Planting
If possible, prepare the soil in a wide area. Apply 50 pounds of a composted organic matter per 10 square feet and incorporate it thoroughly into the top eight to 12 inches of soil with a tiller or shovel. Organic matter holds nutrients and water in the soil and helps prevent stress from wet/dry fluctuations in soil moisture.

Don't fertilize until the plant is established (4 to 8 weeks after transplanting). The majority of Georgia soils are acidic, so initial flower color will likely be blue.

Make certain the top of the root ball is level with the soil surface, and water thoroughly immediately after transplanting. Apply three to five inches of an organic mulch, like pinestraw, pine bark or fall leaves to the soil surface to conserve moisture and control weeds.

Fertilization and Watering
Bigleaf hydrangea responds to several light applications of fertilizer during the growing season. A general-purpose fertilizer, such as 8-8-8 or 10-10-10 applied at a rate of one pound (2 cups) per 100 square feet in March, May and July is suggested. It is not necessary to remove the mulch when fertilizing, but water soon after application to help dissolve the fertilizer and send it into the soil.

Bigleaf hydrangea is a water-demanding plant for the moderate water-use zones of the landscape. Water whenever the plant begins to wilt in the absence of rainfall. The avoidance of plant stress is particularly important during the spring months when the flower heads are forming.

Flower Color
Research has determined that the actual mechanism of color variation is due to the presence or absence of aluminum compounds in the flowers. If aluminum is present within the plant, the color is blue. If it is present in small quantities, the color is "in between," and if it is absent, the flowers are a pink.

The soil pH indirectly affects the color by affecting the availability of aluminum in the soil. When the soil is acid, aluminum is generally more available to the roots. When the soil is alkaline, the availability of aluminum is decreased and the flowers are more pink.

To gradually change flower color from pink to blue, broadcast 1/2 cup of wettable sulfur per 10 square feet and water it in. To make the flowers pink, broadcast one cup of dolomitic lime per 10 square feet and water it into the soil. It may take a year to see a noticeable change in flower color from this treatment.

Another, quicker way to achieve a change in flower color is through liquid soil drenches. To make the flowers blue, or perhaps more blue during the growing season, dissolve one tablespoon of alum (aluminum sulfate) in a gallon of water and drench the soil around the plant in March, April and May. To make the flowers pink, dissolve one tablespoon of hydrated lime in a gallon of water and drench the soil around the plant in March, April and May. Avoid getting the solution on the leaves because foliar damage may result.

Failure to Flower
Failure to flower is sometimes a problem with bigleaf hydrangea. This can be caused by winter injury to the flower buds, pruning in the late summer, growing the plant in too much shade, or applying excess nitrogen fertilizer.

Bigleaf hydrangea forms its flower buds in late summer for the following year, so pruning in late summer, fall and winter will remove potential flowers.

Pruning
Prune bigleaf hydrangea when the flower heads begin to fade. Prune out the flower heads and head back other shoots to encourage branching and fullness. Flower buds will begin forming in late summer for the following season, so avoid pruning after August 1.

Propagation
One of the easiest ways to propagate bigleaf hydrangea is by layering. This is done by digging a trench near the plant and bending a section of limb down into the trench. Use a knife to remove a small ring of outer bark about one inch wide all the way around the limb where it contacts the soil. Then, cover the limb with soil, leaving six to 12 inches of the tip growth uncovered. If layering is done during the summer, the new plant should be ready for transplanting the following winter.

Old established hydrangeas may also be divided in the early spring, by using a shovel to divide the clump. Several plants can be obtained from a well-established clump.

Fact Sheet H-92-011
The University of Georgia and Ft. Valley State College, the U.S. Department of Agriculture and counties of the state cooperating. The Cooperative Extension Service offers educational programs, assistance and materials to all people without regard to race, color, national origin, age, sex or disability.

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Issued in furtherance of Cooperative Extension work, Acts of May 8 and June 30, 1914, The University of Georgia College of Agricultural and Environmental Sciences and the U.S. Department of Agriculture cooperating.

Gale A. Buchanan, Dean and Director