The bigleaf hydrangea can be a popular landscape plant for many in our area.
The bigleaf hydrangea is also called the French, Japanese or snowball hydrangea. This is a popular plant because of the ability of this hydrangea to be planted in the landscape to become a repeat annual bloomer. One cool characteristic is the ability given to the owner to change the flower color from pink to blue or from blue to pink by simply adjusting the soil pH.
Today, I will be sharing information on this popular landscape item from a University of Georgia publication by retired UGA Extension Horticulturist Gary Wade.
For starters, there are more than 500 known cultivars of bigleaf hydrangeas. Bigleaf hydrangea can be divided into two main groups, the hortensias, with the large snowball appearing flower clusters, and the lacecapes, which will have a flat-top appearing flower with fertile non-showy flowers in the center and more showy sterile flowers on the outside.
You need to keep in mind that Bigleaf hydrangea like a planting spot that will provide morning sun, afternoon shade and moist, but well-drained soil. Stay away from planting in hot and dry areas. You can see cold damage to the buds in winter and late spring. This means that you need to be prepared to provide some type of winter protection by covering the hydrangea with an old sheet, blanket or old cardboard container for example when temperatures drop below freezing. If worried about cold damage you can also put a cylinder of chicken wire around the plant and fill with leaves to provide cold protection, according to Wade.
Note that bigleaf jydrangea can be grown fairly easy in containers and can make great plants for patio spots. Growing in containers will give the owner the ability to bring the plant indoors if the night temperature is cold.
If planting hydrangea in the ground, prepare the soil in a wide area. It is suggested to apply 50 pounds of composted organic matter per 10 square feet and try to incorporate into the top 8 to 12 inches of soil with a tiller or shovel. Wade states that organic matter will hold nutrients and also water in the soil and will help prevent soil moisture fluctuations.
Keep in mind to not fertilize until the hydrangea is well established, which should be four to eight weeks after transplanting. Note that most of the soil in Georgia is acidic so the starting flower color will more than likely be blue.
When you plant, make sure the top of the root ball is level with the soil surface. You will need to water well after transplanting the hydrangea. It is suggested to apply 3 to 5 inches of an organic mulch such as pine straw, pine bark or fall leaves to the soil surface in order to help conserve moisture and help control weeds.
The bigleaf hydrangea will like several light applications of fertilizer during the actual growing season. You can use a general purpose fertilizer such as 8-8-8 or 10-10-10 at a rate of 1 pound per 100 square feet in March, May and July. You do not have to remove mulch when fertilizing, but do water soon after you apply the fertilizer.
Keep in mind that the bigleaf hydrangea is a known as a water demanding plant that is best tailored for a moderate water use landscape zone, per Wade. Water the bigleaf hydrangea whenever the plant begins to wilt when you do not have rainfall. It is important to avoid plant stress in the spring when the flowers are forming.
Flower color is important in bigleaf hydrangea. Wade states that research has shown that the actual mechanism of color variation is due to the presence or absence of aluminum compounds in the flowers. If aluminum is present in the plant, the color is blue. If the aluminum is present in small amounts, the flower color will be “in between” and if the aluminum is absent, the flower color is pink.
Soil pH will indirectly affect flower color by affecting the availability of aluminum in the soil. When the soil is 5.5 or lower which would be considered acidic, aluminum is more available to the roots. When the soil pH is 7.0 or higher, this would be considered neutral or alkaline so the available aluminum is decreased so you get more pink flowers.
To gradually change the flower color from pink to blue, you would broadcast 1⁄2 cup of wettable sulfur per 10 square feet and water in. To make the flowers pink, you would broadcast 1 cup of dolomitic lime per 10 square feet and water in. This could take a year to see a for sure flower color change. Wade says another way to get a quicker change in flower color is with liquid soil drenches.
To make the flowers blue or maybe more blue during the growing season is to dissolve 1 tablespoon of alum (aluminum sulfate) in one gallon of water and drench the soil around the plant in March, April and May.
To make the flowers pink, dissolve 1 tablespoon of hydrated lime in 1 gallon of water and drench the soil around the plant in March, April and May.
Remember to avoid getting the solution on the leaves because this can result in damage.