Lush Hydrangeas Grace Yards and Pots
As long ago as 1908, plans for gardens in California put hydrangeas on the east or north side of the house: In a plan for a small property by John McLaren, creator of San Francisco’s Golden Gate Park, “roses, carnations and other flowering plants” line the south and west exposures, while “fuchsias, hydrangeas, etc.” are called for along the north and east walls.
Though time has turned the trusty hydrangea into a garden cliche, it has not diminished their value in the garden--they are still the most dramatic of plants for these exposures. Nothing grows as full and lush against a north- or east-facing wall or fence; few shrubs have flowers so large; not many bloom at the time these do, or for as long.
They also require regular watering, so in the future they may become one of those pampered, cherished plants that get a little extra water. But, they will not disappear because even around the Mediterranean, they grow in gardens that are unirrigated and very dry, often showcased in pots.
The hydrangeas we grow on the Pacific Coast are different from those grown in most of the country. Ours are cultivars of H. macrophylla, developed mostly by the French around the turn of the century, for growing in pots on a summer terrace or indoors for temporary color.
Early varieties had names like “Triomphe de Lisle” and “Mme E. Moulliere.” Early references to these hydrangeas also called them by another botanical name, Hydrangea hortensis. Even further back, hydrangeas weren’t Hydrangea at all, but were named Hortensia, which explains why a famous planting of them in pots is known as the Hortensia Terrace, at the Villa Aldobrandini, at Frascati, just outside Rome.
These are the hydrangeas we grow, and a favored but almost forgotten place for them is indeed in pots. They thrive in containers and look most comfortable in one of those imported Italian pots that measures about 16 inches tall and as wide. Several will make a Hortensia Terrace of your own.
The hydrangeas available today are often simply labeled “blue,” “pink” or “white,” which is really not much help because blue is always suspect in a hydrangea, since the flowers only turn that color in an acid soil, and because the pink can be many shades of that color, from near magenta to a clear, light pink that is more pleasing to most eyes. Some pinks turn an antique mauve that is handsome, even elegant, in the proper setting.
Not many gardeners seem to know much about hydrangeas today, they are so taken for granted (we would be glad to hear from any gardener who might be the exception), so to find out how to grow hydrangeas in California, one must consult rather old books.
Dana Groot, the son of a Netherlands-born wholesale grower with Dutch nursery acumen in his blood, is one of the few who knows something about the plants, and one of the few to sell hydrangeas with their proper names attached (your local nursery can order these from El Modeno Gardens in Irvine).
They offer a number of varieties, including “Kuhnert,” capable of producing clear-blue sepals; “Merritts Supreme,” which can be made dark pink or blue; “Rose Supreme,” the huge-flowered hydrangea seen in gardens with the clear-pink sepals; “Red Star,” with large, brilliant-pink flower heads, and “Sister Therese” with its white sepals that fade to green.
Note that the colored parts of the “flower” are actually sepals, modified leaves that protect the true flower, which on close examination--they are very tiny--will be found at the base. Turning the flower heads blue can be accomplished with a chemical sold by the bag at larger nurseries--aluminum sulfate.
The red anthocyanin pigment in the sepals becomes blue upon complexing with aluminum, abundant in most soils, but unavailable to the plant if the soil is alkaline or if there is too much phosphorous. The color is a reflection of the soil: in acid soils the blue appears; in alkaline soils, which ours tend to be, they become pink. Nurserymen try for a Ph of 5.5 or lower.
Some hydrangeas turn blue easier than others, “Kuhnert” or “Merritt’s Supreme” for instance. And, there are hydrangeas that seem to turn blue with no help from their owners; one must surmise that the soil is for some reason acidic, or that sometime in their past an effort was made to turn them blue, for this is not something that happens overnight.
“Your pink blooms won’t change to blue before your eyes, the results come gradually (if the next crop), over a number of years and you will have to keep up the application at intervals,” is how Californian Albert Wilson put it in his 1949 book, “How Does Your Garden Grow.”
His recommendation (also that of the University of California at the time) was to add one-half pound of aluminum sulfate to every square yard of ground, or three ounces dissolved in one gallon of water for hydrangeas in pots. A modern reference cited by Groot suggests adding the aluminum sulfate to potted plants in September, months before flowers begin to form.
Equally important is using a fertilizer that does not contain much phosphorous, one with numbers such as 15-2-10, or 10-0-0, on the label.
For the clearest blue flowers, use a fertilizer with medium amounts of nitrogen and lots of potassium, but little or no phosphorus. All of this information can be found on the back of the fertilizer bag.
“The all-important requirement of these hydrangeas is water. They should never be allowed to flag for lack of it, especially if they are grown in pots, always in part shade; big pots can take a lot. Open-ground plants need less attention to watering, but even they are greatly improved by regular summer soakings,” pretty much sums up the watering needs (from Sydney Mitchell’s “Your California Garden and Mine,” 1947).
While they certainly aren’t drought-resistant plants, it really doesn’t take more than a watering can full to thoroughly soak a pot or two, and there are plenty of hydrangeas in the ground in gardens that are obviously not watered that often (you can tell because the lawns are suffering from lack of it).
Because of the current water shortage, it would not be a good idea to plant them now, but to buy them in flower and keep them alive in their pots until fall--the more water-thrifty time to plant.
Hydrangeas come into full flower in June and can last easily into late summer or even early fall. The true flowers of course are gone, but the sepals, being modified leaves, live on, changing color as the flowers fade. They can, incidentally, be cut and dried.
It is not necessary to prune a hydrangea, as thousands of untended plants in gardens prove, but to control the size of the shrub, you can prune off branches that have flowered, and nip back the tips of those that haven’t. You can even cut back entire plants, removing two-thirds of the length of the stems.
In containers, Groot suggests cutting back the entire plant by mid-July, leaving just 6- to 8-inch stubs with buds at the base. These will flush out in about two to three weeks and in September will make buds that will bloom the following spring.
Don’t prune again or you may lose next year’s flowers, though you can thin out some branches in August for a better placed display of flowers. From these nubbins will sprout a bush that is 3 to 4 feet around the following summer.
They will lose their leaves in winter, but that is not the time to prune, or you will lose future flowers. If all of the leaves do not fall off of their own, pick them off by hand in mid-November.
This will help the flower buds develop and will get rid of any mites, whitefly, powdery mildew or green peach aphids that may be waiting for winter to pass. These pests are the most common on hydrangeas, though seldom serious enough to warrant spraying.
That they do so well against the walls of a house hints at how much light they need. They will grow under the canopy of a tall, airy tree, but they prefer about half a day of sun (as found against an east wall) or at least a bright, clear sky overhead (against a north wall). They are not so much shade plants as they are half-shade shrubs or even half-day plants.
The 1915 reference “California Garden Flowers” by E. J. Wickson suggests giving them “more or less shade, according to the fervency of the local sunshine.”
One can only guess what the “etc.” in McLaren’s 1908 plan called for, but the secret to a happy, healthy hydrangea would seem to be not to crowd it with other plants or with other hydrangeas. The best are most often seen growing nearly alone or at least in clear control of the garden bed.
Possible companions would be fuchsias near the coast or camellias anywhere, if they are not planted too close to the hydrangeas. Hydrangeas grow at least four feet across, and many make it to 6 or 8 feet. Pink hydrangeas and foxgloves or the foxglove-like Rehmania would be a stunning combination.