By MaryJo Broussard, Mobile County Master Gardener, www.mobilecountymastergardeners.org
Hydrangea is an iconic flower in our Southern gardens because we are blessed to have an abundance of rain to keep them happy.
Blue mophead hydrangea is the most often seen, but there are many other colors, varieties, sizes, and shapes. One can surely fit your landscape plan. Most are deciduous, losing their leaves in winter, with many retaining the dried flower heads throughout. Some can take more sun than others, so reading the label on each is necessary before placing them in your landscape. Some varieties form thick bushes and some can be quite tall, offering something for every taste and location.
We are often asked about pruning. It varies among each variety, so it pays to know the variety in your landscape. Hydrangea either bloom on new wood or old wood, depending on variety. A rule of thumb is that Oakleaf and Mophead varieties are not rebloomers so bloom on old wood. Their pruning needs to be done immediately after flowering to allow stems to grow into old wood. If you wait to cut these in spring, you will be removing all the flower buds, resulting in no flowers that year.
Smooth and Panicle varieties (such as Limelight) bloom on new wood so you can wait until after winter to prune. I usually do this about early March which allows time for bud set, avoiding the danger of cold hurting the new buds.
Now let’s talk about color. We all love the deep glow of the blue mopheads, but they can also come in pink, purple, or white, depending on the soil pH. Our local soil is naturally more acidic, pH 5.0 - 5.5, so we usually have blue blooms, neutral to alkaline soil has a pH of 5.5 – 6.5 and will cause purple, or a mixture of blue and pink blooms. Alkaline soil pH 6.5 – 7 will produce pink blooms. Send a soil sample from where you grow or plan to grow hydrangea to have an idea of how much of what type amendments you will need to add to change the blooming color.
If you have the blue color and want it to bloom pink or even purple, it’s easy enough to do if you plan ahead. You can adjust soil pH by adding amendments to your soil. Understand that if your soil is not kept at the different pH, your blooms will return to their native color. See Routine Soil Testing Analysis Form (auburn.edu) for instructions for a soil test and how to change soil pH.
To confuse matters, some varieties of hydrangea, especially newer varieties, will produce blooms that will not change in different soil types. The Panicle and Oakleaf hydrangea are white with tinges of pink or green as they age, but the color is white. White varieties do not turn lighter or darker. They may turn slightly green with age but stay white as they are bred to do.
All hydrangea require moist conditions, moist but not wet. Our average rainfall will usually do the trick. Do pay attention to your plants as they will tell you when they need extra moisture by drooping leaves. Water well then, especially at the root area. Morning sunlight is great, but afternoon will result in burned plants, so a half-day of sunlight is all they need. Also, too much shade will result in poor quality of life and few blooms.
Your oakleaf hydrangea are from more rocky or drier regions so they can do with less soil moisture and take more sun, even some afternoon sun, but not all day long. Leave the blooms on these plants to dry and gradually turn a bronze color which goes great in flower arrangements. Dry mophead blooms by cutting them when they are at their fullest, putting them in a vase with about 1” of water and letting it slowly evaporate. Then add them to your arrangements and continue to enjoy your hydrangea all year long.