Campbell Vaughn: Pink or blue? You can influence the color of hydrangea

For some good southern garden hydrangeas, this is a good time of the year. Something in the blue mop-head hydrangea allows gardening juice to flow. These southern gems are called large-leaf hydrangea or commonly known as large-leaf hydrangea, French hydrangea or snowball hydrangea.
There are more than 500 known large-leaf hydrangea varieties in the nursery trade. They are divided into two categories: Hortensias with large snowball-shaped flower clusters and lace hydrangea, which usually have some flat-topped (lace flower) flowers. With fertile, non-showy flowers in the center, and more colorful, sterile flowers on the outside. The plant size varies from 4 feet to 12 feet, depending on the variety.
The criteria for my decision to continue planting these southern beauties are morning sunshine, afternoon shade and moist, well-drained soil. Avoid planting it in hot, dry, and exposed places. Large-leaf hydrangea is susceptible to freezing temperatures, so looking for some protection against the cold is also a consideration. The cold in late spring can freeze the leaves and occasionally damage the flower buds. Our April freeze proved this point. French hydrangea can be easily grown in a container and is an excellent garden plant. Another advantage of growing plants in containers is that it can be moved indoors on cold nights.
Bigleaf hydrangeas respond to several fertilizations during the growing season. It is recommended to apply general-purpose fertilizers, such as 8-8-8 or 10-10-10, at a rate of 1 pound (2 cups) per 100 square feet in March, May, and July. It is not necessary to remove the mulch when applying fertilizer, but water immediately after application to help dissolve the fertilizer and send it into the soil.
Hydrangea macrophylla is a water-requiring plant, which is most suitable for areas where water is easily available. In the absence of rain, whenever the plants begin to wither, be sure to water them. It is important to avoid stress on the plants during spring blooming. Apply 3 to 5 inches of organic mulch, such as pine grass, pine bark, or fallen leaves, on the soil surface to retain moisture and control weeds.
Did you know that you can actually change the color of the flowers on these hydrangeas from blue to pink? The science behind the ability to change the color of flowers comes from the ability of plants to absorb aluminum. When the pH of the soil is lower than 5.5, hydrangeas can better absorb aluminum, which makes the flowers blue. When the pH of the soil becomes more alkaline (6.0 and above), the hydrangea cannot absorb aluminum, and the color changes to pink. Since most of our soil is acidic, these hydrangeas are naturally blue.
To gradually change the color of the flower from pink to blue, spread half a cup of wettable sulfur every 10 square feet and water it. To make the flowers pink, spread a cup of dolomite lime every 10 square feet and pour it into the soil. It may take a year for this treatment to see a significant change in color.
Another way to change the color of the flower more quickly is by soaking the liquid soil. To make the flowers blue, or bluer during the growing season, dissolve 1 tablespoon of alum (aluminum sulfate) in 1 gallon of water and soak the soil around the plants in March, April, and May. To make the flowers pink, dissolve 1 tablespoon of hydrated lime in 1 gallon of water in March, April, and May, and then soak the soil around the plants. Avoid applying the solution to the leaves, as it may cause foliar damage.
My poor friend Jason called me and said that his hydrangea this year is very beautiful, but there is only one flower. He received some bad suggestions for pruning them, and in February cut them off and cut off all potential buds.
When the flowers begin to fade, it is best to trim large-leaf hydrangeas. Prune flower heads and long branches to promote fullness. Flower buds will begin to form in the late summer of the next season, so avoid pruning after mid-August. Sometimes it is necessary to prune plants after severe winter to remove damaged leaves. Although this promotes vegetative growth at the expense of flowers, removing the damaged leaves in winter is more beneficial to the health and beauty of the plant.
Remember, these shrubs are deciduous, so in winter they will have no leaves for 3 to 4 months. If you can find a suitable location, these hydrangeas can be the highlight of your landscape.
Contact Campbell Vaughn, UGA Agriculture and Natural Resources Agent, Richmond County, by emailing

Post time: Dec-07-2021


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