One of the prettiest Southern shrubs, which I’m ashamed to admit that I don’t have in my yard, is the hydrangea. Every year when I see their showy blooms, I ask myself why I haven’t planted any yet. These plants would be a beautiful addition to any landscape that has afternoon shade and well-drained soils.
Probably the most common hydrangeas, the bigleaf (Hydrangea macrophylla), can be divided into two categories. Plants with the large, snowball-like clusters of flowers are referred to as hortensias, while the flat-top forms with nondescript flowers surrounded by a ring of showy flowers are referred to as lacecaps.
A close cousin is the oakleaf hydrangea (Hydrangea quercifolia). This plant, a Georgia native, has large “cones,” or panicles, of white flowers that eventually turn light purple or pink. Also not to be forgotten is the limelight hydrangea (Hydrangea paniculata), which blooms large panicles of creamy white flowers and does better in the sun than the fore mentioned species.
▪ Flower color: One of our common hydrangea questions is how to determine, or control, the color of the blooms. Interestingly, flower color — pink, blue or any shade in between — is actually determined by the presence of aluminum in the soil. Since soil pH dictates how readily roots can absorb nutrients, adjusting the pH is key. The more acidic the soil, the more blue the flowers are, while alkaline soils tend to have pinker blooms. Interestingly, some of the newer varieties are true to color and cannot be changed.
▪ Disease: Hydrangeas are susceptible to several foliar diseases that can cause purple spots on the leaves. Two common diseases are cercospora, which primarily affects leaves, and anthracnose, which can affect leaves and blooms. The diseases will become more noticeable later in the summer if the rains continue and/or overhead irrigation is used. These diseases are common on hydrangeas in the late summer and autumn. A wet, humid environment increases the severity of these diseases.
The good news is that these leaf spot diseases will rarely kill the plant. Fungicides such as chlorothalonil or thiophanate methyl can be applied (and repeated every 10-14 days) when symptoms first appear, but are generally not warranted. Proper irrigation and removal of leaf litter in the fall will likely prevent major problems.
▪ Pruning: Another common question about hydrangeas is how and when to prune them. In general, major pruning and shaping of these shrubs should be done immediately after flowering. Pruning can improve plant vigor, overall shape and bloom volume. Remove all dead wood and cut about 1/3 of the older stems to the ground. Since plants bloom on the previous year’s growth, avoid pruning them after the start of August (except limelight hydrangeas, which bloom on new wood).
If your landscape doesn’t already boast at least one of these showy and reliable plants, consider adding some this fall. Find a well-drained spot that receives morning sun and afternoon shade. It is on my “to do” list!
For more information about planting, using solutions to adjust color and much more, visit extension.uga.edu/publications/detail.cfm?number=C973 or your local Cooperative Extension office.
Contact Macon-Bibb County Cooperative Extension agent Karol Kelly at firstname.lastname@example.org.