Colorful, versatile hydrangeas

Hydrangeas in bloom and massed together in summer can make a breathtaking sight. Some hydrangeas’ flowers and leaves change color as fall arrives and some have attractive peeling bark, visible in the winter.

Hydrangeas in bloom and massed together in summer can make a breathtaking sight. Some hydrangeas’ flowers and leaves change color as fall arrives and some have attractive peeling bark, visible in the winter.

On a recent trip to northern France, I was blown away by hedges of brilliantly colored hydrangeas, often planted alongside thatched cottages and other traditional country dwellings. The pom-pom flower heads, set against deep green leaves, resembled a child’s drawing made with pink, blue, purple and green crayons.
In the past, I’d considered hydrangea blossom less interesting than many other flowers — roses, passionflowers, hollyhocks, to name just a few. But the effect of massed flowers in striking shades of pink, blue and purple — sometimes all together in one hedge — took my breath away.
Then I heard that one could change the color of a hydrangea’s flowers to blue by burying nails or slate tiles (a typical roofing material for 19th century houses in that part of France) in the soil. Intrigued, I decided to dig further.
Back home, one of my gardening books described such claims as an old wives’ tale, but several others gave instructions for mixing up a chemical brew that could turn pink hydrangeas blue and blue ones pink, although the latter was said to be more difficult. No mention of nails and slate tiles.
The website plantaddicts.com noted it was much easier to change the color of a hydrangea growing in a container than one in the ground. Details of the recipe I found for this alchemy will appear a few paragraphs down, but the gist of it is to change the soil’s chemistry to make it more acidic or more alkaline. Acidic soil tends to produce blue and purple hydrangeas, alkaline soil pink ones, according to what I read. But that’s only part of the story. White flowering hydrangeas cannot change color, no matter what you add to their soil.
One reason I’ve fallen for hydrangeas is that the blue ones like growing in acidic soil, which we have in spades in Dorchester. Blue is such a lovely color for flowers, particularly during our sweltering summers when it gives the illusion of coolness.
In fact, I already have two hydrangea shrubs, but they flower in pink. (The grass is always greener on the other side.) Not that I don’t love them. Every summer except this one, I’ve nursed them back from the brink after drought and wind clobbered them at the height of their blooming. Sometimes I watered them twice a day. This summer has been wildly different, with masses of rain in between weeks of drought. My hydrangeas have grown enormous.
One book I consulted said hydrangeas do especially well in beachside gardens (my beach is a marsh). Another said they love sun, while a botanical encyclopedia advised shade or part-shade. Most of the hydrangea hedges I saw in France grew in full sun. But here in Dorchester, mine can’t take too much sun and prefer shade for at least part of the day. The real killer is wind. Most hydrangeas are small to medium-sized deciduous shrubs. But Climbing Hydrangea (hydrangea petiolaris) is a self-clinging vine that likes to face north, which few plants do. So, it’s a treasure. The plant can grow more than 50 feet and produces white blossom in summer. It’s perfect for decorating a boring or unsightly wall.
Many are the charms of hydrangeas and there are dozens and dozens of different types to choose from. If you want a flowering and easy to care for hedge, consider “Limelight,” which flowers in whitish-green, or “Annabelle,” a so-called smooth hydrangea (hydrangea arborescens), which produces large clusters of white flowers, sometimes 10 inches across.
As for livening up the garden in fall and winter, oakleaf hydrangea (h. quercifolia) starts out with white flowers in summer, then they turn pink and violet in cooler weather. Its leaves go from green to burgundy red in the fall and when the leaves have fallen, you’ll notice its attractive peeling bark. The shrub loves the heat and hates standing water. What’s more, it’s native to North America.
One of the easiest hydrangeas to grow is panicle hydrangea (h. paniculata), which also produces white blossom which turns pink as the season progresses. Its stems can be green or burgundy red. Its flowers may come in the form of conical balls or lacey, flat heads.
Some hydrangeas have round balls of densely massed flowers, called mopheads, while others produce lacecaps, flat heads composed of tiny flowers in the center, surrounded by larger florets. To me, the lacecaps look particularly attractive. Some outstanding blue ones include: “Blue Sky,”“Blue Wave” and “Bluebird.” All grow about five feet tall and wide.
As for the recipe to change hydrangea flowers’ color, scientists have determined that some types, particularly “big-leafed” hydrangea or hortensia (h. opuloides), need aluminum to produce a rich blue color. But aluminum can only be accessed by these plants if the soil they’re growing in is quite acid: 5.2 to 5.5 on the pH scale. One way to make soil more acid is to dig in coffee grounds and kitchen compost.
Some big-leafed hydrangeas will change color when the soil chemistry moves just half a point in either direction. Just a little more acidity will make pink blue, and a little less acidity makes blue pink. Other types of hydrangea may not switch color, but their hue will become richer.
The website plantaddicts.com says that for a plant in the ground – it must be at least two or three years old – water well, then give a gallon of water in which you have mixed one tablespoon of aluminum sulfate. Repeat throughout the season. For a potted hydrangea, use half a tablespoon of aluminum per gallon of water. Do this cautiously, because too much can burn the plant’s roots.
A fertilizer low in phosphorus and high in potassium, such as 25/5/30, also will help produce a good blue. And your water’s pH should not be higher than 5.6, so you may need to test the water.
Personally, I might just buy a blue hydrangea and hope for the best! In the meantime, happy gardening!
Editor’s Note: Laetitia Sands is a master gardener in Dorchester County.

 

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