Hydrangeas are a popular plant given on Mother's Day. As children, and even adults, our mother's expressions are often litmus test on whether an idea or situation is right or wrong, even when we don’t solicit their advice. Like our mothers, hydrangeas (with some exceptions) are a litmus test of the environment surrounding their roots.
Except for a few species, hydrangea flowers will be blue or purple when grown in acidic soil (pH below 7) or pink or red in alkaline soil (pH about 7). Bloom color can be changed from pink/red to blue/purple by adding ¼ cup of aluminum sulfate around each plant and repeat again in 6 months. To get pink flowers from a plant that produces blue ones now add 2 to 3 tablespoons of lime around each plant. This can take 1-3 years depending on the soil. Which, like our mothers always tell us, good things are worth waiting for.
Most are familiar with the classic mophead hydrangea (Hydrangea macrophylla var. macrophylla) also know as bigleaf hydrangea. Lacecap is a variety of this species. These prefer light shade or filtered sun, especially during the heat of the day. They bloom on old wood (previous year’s growth); prune canes after flowering, but before August 1st to reduce size or maintain shape. Do not remove more than 1/3 height from the canes. ‘Nikko Blue’, ‘Endless Summer’, and ‘PennyMac’ (2012 Louisiana Super Plant) are all popular cultivars. Endless Summer and PennyMac will flower on new growth as well. Prune these when the flower heads turn green, cutting off the faded flower heads with stems about 4 to 6 inches long (these dry beautifully). To reduce the size of your plant, cut longer stems and shorten any other shoots as needed to achieve the desired results. H. serrata is a similar species but stays more compact.
Smooth (H. arborescens) and Panicle hydrangea (H. paniculate) are two species which bloom on new wood (the current year’s growth). Panicle hydrangea can tolerate full sun but prefer some shade in the afternoons. Pruning for both species is done during late winter or early spring, before new growth appears, to about one-third of the plant’s height or down to about 1 foot in height. H. arborescens cultivars include: ‘Annabelle’, ‘Hayes’, and ‘Starburst’. H. paniculata cultivars include: ‘Tardiva’, ‘Unique’, ‘Pink Diamond’, and ‘Limelight’ (2018 LSU Super Plant). Panicles are an exception to the soil pH rule. Most have large clusters of white flowers in summer that fade to shades of pink or red before drying to beige.
Oak Leaf hydrangea (H. quercifolia) is a native species named for its oakleaf shaped leaves which have outstanding fall color. These can grow to be large shrubs and are often found in hardwood forest. Plant in areas with morning sun and afternoon shade. Blooms are creamy white, elongated panicles up to 12 -inches long. Some common cultivars are ‘Alice’, ‘Ellen Huff’, ‘Snow Flake’ and ‘Snow Queen’. Like panicle hydrangeas, their flowers remain white (or light pink) regardless of soil pH.
Whichever species of hydrangea you choose, be sure to read the description. Some can grow to be quite large. All prefer loose, well-drained soil. If your yard is full sun to part shade, choose a panicle hydrangea, all others prefer part shade, especially during the heat of the day.