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Hydrangeas: Not Just for Grandma's Garden Anymore!

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Oh, my aching muscles...

By Mary Gutierrez

h_endlesssummer3.jpg
Mophead and lacecap hydrangeas adorn the partly-shaded garden. Author's photo.

Hydrangeas evoke images of grandmother’s garden. You may recall the large, rounded shrubs and their heavy pastel flowers with fondness—or distaste. Whether you’ve always loved hydrangeas or merely tolerated them, I suggest you reevaluate the genus. Recent hydrangea introductions offer exciting options for your garden.

While this review is by no means comprehensive, perhaps it will whet your appetite to learn more about these late summer beauties.

Hydrangea macrophylla

Hydrangea  macrophylla is the species name of both mophead and lacecap hydrangeas. These shrubs possess medium-sized smooth leaves that are attractive as long as the plant is healthy. Any nutrient problems will quickly manifest in the form of chlorotic leaves.

To me, mophead hydrangeas add a lush, abundant feeling to a garden. Their billowing form and heavy, rounded flowers make a luxurious statement.  Lacecap hydrangeas are identical in leaf and form to their mophead sisters—only the flower differs. Lacecap inflorescences are broad, flat-topped corymbs of tiny fertile flowers, surrounded by a ring of sterile florets. I think lacecaps are slightly more refined than mopheads, though they can be just as showy. Macrophyllas thrive where they receive a few hours of sun daily. As long as your summers are mild, they can take a half-day of sun or more. Conversely, all-day deep shade will cause flowering to be sparse.

Macrophyllas are not drought-tolerant though an old, established shrub will get by with less water. They prefer a slightly acid soil because nutrients the plant needs are unavailable in very alkaline soils. A high pH will result in the telltale chlorotic leaves. Furthermore, moving the pH scale to either end of the spectrum can affect flower color. (See the sidebar on page 13.) An average garden soil enriched with compost will make your macrophylla thrive.

Macrophyllas can be imposing plants, reaching seven to ten feet tall. Being deciduous, they can also leave a substantial void in the garden come winter. I intersperse them within a mixed border that includes evergreens to minimize gaps in winter.

Pruning H. macrophylla is considered tricky. Improper pruning is often blamed as the culprit when gardeners complain that their hydrangeas don’t bloom. Many web sites and references will tell you that you must prune your H. macrophylla in late summer or it will be ruined for the next season. I might get hate mail for this, but I differ with most experts. To begin with, I’ve pruned my H. macrophylla ‘Ayesha’ in late winter/early spring for years, and have always had summer flowers.

The advice of hydrangea guru Glyn Church backs up my experience. He suggests several approaches (and I paraphrase): a) For an older, too-woody plant, remove two or three of the largest stems to the base of the plant. Then trim the tops of remaining stems to just above a pair of large flower buds. b) Prune the plant lightly overall, cutting back to just above the largest buds (these are next summer’s flowers). Or, c) Remove all thin, spindly growth, leaving the strongest stems. Cut back to the lowest set of big buds. You will have fewer—larger—flowers with this technique.

I think the key with all these methods is to discern between the big, fat flower buds higher up on the stems and the smaller leaf buds below that go all the way to the base of the plant.

If this sounds like too much to think about, you’ll be interested in the new reblooming macrophyllas that produce flowers early in the season on old stems and again on new growth. Or, plant small varieties that don’t need much pruning. Breeders continue to introduce smaller plants, suitable even for container culture.

Hydrangea arborescens

I grew up in a house that had H. arborescens ‘Annabelle’ outside the dining room window. (We called it a snowball bush—a common moniker.) Every year or so, we’d hack the daylights out of it and by the end of summer it was lush and in full bloom.

H. arborescens is one of two North American natives, growing wild from the Eastern Seaboard south along the Appalachian range. The species is extremely hardy, more so than we’ll ever need in the maritime Northwest. And it’s drought-tolerant, too, once established. H. arborescens enjoys full sun and decent drainage—other than that, it’s not fussy about soil. Regardless of soil pH, it will always have white flowers. Better yet, it can be pruned while dormant without fear of harming next season’s bloom.

The only reason I can think of that more gardeners in our region don’t grow this plant is that we don’t have to. Our mild climate allows us to grow the macrophyllas that our Midwestern countrymen cannot.

Hydrangea quercifolia

The oakleaf hydrangea (so-called because its leaves resemble an oak’s) is a lovely plant that should be more widely grown. This is the second American native, growing further south than H. arborescens but also in the Appalachians.

The oakleaf has three strong seasons of interest. In spring, its large leathery leaves emerge, quickly followed by green flower buds. Later, large panicles of white flowers age to pink and as the weather cools the leaves take on burgundy tones. A moderately large shrub, the oakleaf will reach five to seven feet tall. It performs best in full sun with good fall color and abundant flowering. It enjoys moderately rich, moist soil, but needs good drainage or can suffer from root rot. It is not particular about soil pH. Pruning consists of deadheading and removing dead wood.

Hydrangea paniculata

Hydrangea paniculata ‘Grandiflora’ is the peegee hydrangea. The inflorescences resemble an oakleaf hydrangea in that they are large and they open white. These blossoms are dense, though, often bending the stems beneath their weight.

Paniculatas are cold hardy, easy to grow, and long-lived. They are not particular about soil and grow best  in full sun. Like H. arborescens, they bloom on new wood so can be pruned when dormant. It isn’t necessary to prune every year, unless you’ve planted them in a place that can’t accommodate their size. Peegee is the only hydrangea that is sometimes trained to a standard. Breeding has brought renewed interest to this species, offering a greater range of plant sizes and flower tints.

Hydrangea aspera

H. aspera is another multi-season plant. In spring its large, felted leaves emerge followed by corymbs of tight brown fuzzy flower buds. In July, the purple and white lacecaps open reaching eight or ten inches across. A large crown of purple fertile flowers form a mass, surrounded by white sterile florets. The flower is elegant and refined, the perfect adornment to this distinguished plant. While the fall foliage is an unspectacular yellow, it falls quickly, revealing shaggy peeling light-brown bark.

H. aspera is perfect for the back of the border, its deep green, light-absorbing leaves providing a canvas for other plants. Grow hosta, podophyllum, ferns, asarum, trillium, paris and other woodland treasures beneath your H. aspera and you’ll be the envy of highbrow plant aficionados. H. aspera grows in full sun or partial shade, and blends impeccably in a woodland setting. Grow in average garden soil, amended with compost and provide water as needed.

Don’t Forget the Climbers

No discussion of hydrangeas would be complete with mentioning the climbing members of the clan. Hydrangea anomala subsp. petiolaris is fantastic growing up one of the enormous evergreens that many Northwesterners have on their property. After a few years settling in, this climber will eventually grow as far as you will allow it. In summer, it produces elegant white lacecap flowers.

Schizophragma hydrangeoides ‘Moonlight’ is a hydrangea cousin that has beautiful mottled leaves topped by white lacecap flowers in summer.

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H. 'Endless Summer' in a slightly acid soil. Author's photo.



Changing Flower Color in H. macrophylla

Hydrangea macrophylla is unique in its response to soil pH. The same cultivar grown in different gardens can exhibit either pink or blue flowers depending on the soil’s alkalinity or acidity. 

This process is governed by the availability of aluminum in the soil; the accumulation of aluminum in the flower itself causes it to turn blue. Lime added to the soil produces pink flowers because it inhibits the availability of aluminum. Blue flowers are encouraged by making the soil acidic and/or by adding aluminum sulfate to the soil. 

The process is complex, though, and it can take years to change flower color. In some soils it is an uphill battle with unsatisfying results. It is best to learn to love what you have rather than adding more toil to your gardening. If you absolutely must have a blue hydrangea and you live on alkaline soil, consider growing your plant in a large container where pH is much easier to control.

While many macrophyllas have extremely variable color, others have a color “inclination” and are more resistant to attempts to change them. The cultivars listed below will try to stay true to their color. Encourage a pink or red cultivar with a little lime; or add a little aluminum when planting your blue cultivar.

Red

Red Emperor, Alpenglow, Arthur Billard, Harry’s Red, Lady in Red, Masja

Pink

Madame Pluecoq, Mrs. W.J. Hepburn, Princess Beatrix

Blue

Blue Prince, Gentian Dome, Générale Vicomtesse de Vibraye, Hamburg, Mathilda Gutges


Hydrangea Sources

Joy Creek Nursery
(mail order and retail)
20300 NW Watson Rd.
Scappoose, OR  97056
503-543-7474
www.joycreek.com

Hydrangeas Plus (mail order)
www.hydrangeasplus.com
503-651-2887
866-433-7896

Forestfarm (mail order)
990 Tetherow Rd.
Williams, OR  97544
541-846-7269 (phone orders)
541-846-6963 (fax orders
www.forestfarm.com

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Hydrangea aspera. Author's photo.

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