Consistent rebloomers, new colors and petal shapes expand the field of this traditional favorite
Hydrangeas are hot, and an increasingly crowded field of new introductions is scrambling for market share.
In 2014 alone, some 83 new hydrangea varieties hit the market, including 67 H. macrophylla selections and 19 H. paniculata selections, according to Kristin VanHoose, owner of Amethyst Hill Nursery and Hydrangeas Plus, in Aurora, Oregon.
Why the robust interest in this genus?
Endless Summer®, the first repeat-blooming (aka “remontant”) H. macrophylla mophead to hit the market, burst onto the scene in 2004. Discovered by Dr. Michael Dirr in his breeding program at the University of Georgia and released by Bailey Nurseries, Endless Summer was unique in its ability to flower on both old and new wood. Doing so greatly extended the bloom potential of these old-fashioned flowering shrubs.
Since its launch, some 20 million plants of Endless Summer have been sold worldwide, and reblooming potential has been widely touted among other introductions too.
Proof is in the reblooming
The claim of remontancy is not always borne out by trials though.
According to Dirr, “many of the recent introductions are recycled pot-plant types. Be leery of their advertised garden adaptability and particularly the claim of reblooming.”
Dirr’s Plant Introductions Inc. (PII) in Watkinsville, Georgia, which now operates as the in-house breeding program for Bailey Nurseries, breeds, evaluates and introduces plants. It has tested many of the new hydrangea introductions to determine whether they perform as claimed.
The extremely harsh winters of 2013–15 provided an opportunity to judge whether H. macrophylla plants were in fact rebloomers. From Maine to Georgia, hydrangeas were devastated by the combination of early fall freezes, occurring before stems and buds had hardened, and a spring freeze when leaves were emerging. All H. macrophylla plants at the PII in-ground test areas were killed to the crown.
Without old wood to bloom on, only true rebloomers would flower the following summer. Without reblooming genes, though, “there was precious little flower development,” Dirr said.
PII/Bailey’s new introduction, BloomStruck™, passed the test. At PII, plants frozen to ground level recovered and produced flowers or buds on every terminal by mid-September. During the five years BloomStruck was evaluated before its release, it was again slammed by 50 days below zero, with a low of –28 F at Bailey Nurseries in St. Paul, Minnesota. There, too, it regrew and produced flowers on every terminal by late June.
BloomStruck is “the most potent mophead rebloomer in my experience,” Dirr said. Rated to USDA Zone 4, it is a complex hybrid with 25 percent H. serrata and 75 percent H. macrophylla in its genetics, which accounts for the added hardiness.
“I believe there is an opportunity to increase stem and bud hardiness of the remontants by utilizing hardy H. serrata selections,” Dirr said.
With vivid purple or rose-pink flower heads all summer, this improved cultivar also achieves other goals of the ongoing PII breeding work: sturdy purple-red stems, more compact habit, heavily textured, dark green foliage and great resistance to mildew.
PII is also working to develop selections with deep purple-black foliage and double flowers.
In the Minnesota tests, Twist-n-Shout® came in a close second for reblooming. Another member of the Endless Summer collection, it is the first reblooming lacecap H. macrophylla. The conditions proved to be tough competition for the original Endless Summer, which produced only one flower the same year.
Blushing Bride®, the fourth member of the Endless Summer group believed to be remontant, produced none. The pure white mophead with blooms that turn pink at maturity is “still one of the most beautiful hydrangeas from the Georgia program,” Dirr said. “PII has yet to breed anything better in this color range.”
Still, claims of reliable remontancy did not materialize as expected in these cases.
PII also tests introductions from other sources that claim to rebloom, since that trait is the focus of PII’s hydrangea research. Seeking direct scientific information about certain plants, PII has even submitted plants for DNA testing when trials have not produced expected results.
For instance, the newly released L.A. Dreamin’ from Ball Ornamentals Inc. came from a plant that had been seen growing in a Michigan yard. Its blooms were a combination of blue, pink, purple and mauve, all on the same plant that had clearly survived the Michigan winters. John Bakale of Michigan Evergreen Nursery took cuttings, shared them with the local Ball rep and named it to honor his late daughter, Lindsey Ann.
But is it a remontant H. macrophylla?
When Dirr tested it for three years, he observed no rebloom, so he sent it to Dr. Tim Rinehart at the USDA, ARS, Southern Horticultural Laboratory for DNA testing. Results showed that L.A. Dreamin’ was not, in fact, a new plant. Rather, its DNA matches an old pot-plant cultivar called ‘Mathilda Gutges’.
Does it matter that a plant does not have a unique genetic makeup?
According to Dirr, it is more important to identify superior garden plants with traits that will assure strong performance over time. Rushing a plant to market based on claims that are not substantiated by years of trials causes an overwhelming and confusing glut of offerings for consumers.
“The pot-plant types look great when purchased and then do nothing in subsequent years,” he said. “Bailey has tried valiantly to distinguish plants in the Endless Summer brand as garden hydrangeas that will perform over time.”
Truth in advertising was on people’s minds at the three-day Hydrangeas 2015 International Conference, held last summer at Heritage Museums and Gardens in Sandwich, Massachusetts.
Kristin VanHoose was among the growers, academics and other hydrangea experts who attended the conference. One of the relevant messages she sought to share in her talk was the importance of being truthful about the characteristics of plants.
VanHoose trials many hydrangeas at her site in Oregon’s Willamette Valley, a place known to be friendly for the culture of hydrangeas. Some H. macrophylla cultivars said to repeat bloom have not performed for her, but that is not the only factor in considering the usefulness of new hydrangeas. Researchers and growers have been seeking interesting leaf colors, shapes and textures, good fall foliage color, sturdier, colorful stems, compact habit and increased hardiness that warrant bringing new or newly rediscovered hydrangeas to the market.
One recent introduction is Blue Enchantress® (H. macrophylla ‘Monmar’ PP25209). It is derived from a plant found in a private garden in San Mateo, California, that the homeowners took to Monrovia. The company took a cutting, stabilized it with other varieties, and Blue Enchantress was born.
“It’s been available for a few years and much to our delight, that purple stem has stayed true,” Monrovia spokeswoman Katie Karam said. “It was and remains the only repeat blooming mophead hydrangea with dark stems. It is our best-selling hydrangea.”
The company has additional new hydrangeas coming out in the spring.
Among other H. macrophylla varieties, VanHoose likes ‘Sensation’, which boasts “stunning” picotee petals, white edges rimming hot pink, purple or royal blue florets. It is a stronger, sturdier alternative to ‘Harlequin’, she said.
“People like white,” VanHoose said. ‘Princess Juliana’ has been the best-selling white H. macrophylla for her and boasts strong disease resistance.
A good place to look for other white options is among the many new introductions of H. paniculata.
According to Dirr, more than 100 H. paniculata cultivars were available in 2015, but the species is “more forgiving in the garden,” he said. “They flower on new and old wood, and the move to smaller, compact habits is opening new markets.”
With better cold hardiness (USDA Zone 3), “H. paniculata grows everywhere,” VanHoose said. After a harsh winter in Oregon, all the H. paniculata plants came back and bloomed, she said.
The species does not like heat or drought, though, and plants and blooms can get huge, so one challenge when selecting a good candidate for the garden is whether stems are sturdy enough to hold the flowers upright.
VanHoose likes the smaller cultivars Little Lime® and Bobo® from Proven Winners, and Baby Lace® from Gardeners Confidence Collection. A smaller version of ‘Limelight’, Little Lime stays “reliably small” (3–5 feet tall and wide). Its green panicles, which soften to pink, are supported on sturdy stems. Bobo, from a breeding program in Belgium, is even smaller at only 2–3 feet tall by 3–4 feet wide with white flowers that turn pink in fall. Sturdy stems hold the flowers upright. Baby Lace stays small (3–4 feet) and is loaded with petite, lacy white blooms.
H. arborescens is the source of many new introductions too. “Their genetic potential has not been fully explored or tapped,” according to Dirr. Native to the East Coast, H. arborescens blooms on old and new wood and boasts remarkably frost-tolerant foliage.
“Breeders are at the tip of the genetic iceberg as far as introducing new cultivars that are different from the time-honored ‘Annabelle’,” Dirr said. PII, for instance, is “relentless in pursuit of improved H. arborescens and the future portends great advances.”
Invincibelle® Spirit II, a new and improved selection from Dr. Tom Ranney’s breeding program at North Carolina State University, will be available as part of the Proven Winners shrubs line in spring 2016. Claiming richer pink color, stronger stems and “even better reblooming,” this plant is also a fundraiser for the Breast Cancer Research Foundation.
Oakleaf hydrangea is the source of some outstanding new introductions too. ‘Ruby Slippers’ is a compact H. quercifolia that produces exquisite fall foliage. “Hybridized for smaller landscapes and containers, I have yet to need to prune my five-year specimen that has grown to just 4 feet,” VanHoose said. It produces white inflorescences that turn pink to rose and hold their color. Introduced by the U.S. National Arboretum breeding program in McMinnville, Tennessee, this “jewel of a plant” combines the upright habit of ‘Snow Queen’ with the compact nature of ‘PeeWee’.
New test garden planned
The future is bright for hydrangeas, and a new national hydrangea test garden will help identify the best of the best. From an idea that emerged at the Hydrangeas 2015 International Conference, the new test garden will be housed at the Heritage Museums & Gardens, which already boasts a hydrangea collection of 155 species and cultivated varieties.
Staff and interns will document and collect data on plant performance that will help growers perfect new hydrangea varieties and evaluate how such varieties perform in New England, one of the country’s largest markets for hydrangeas.
The test garden will expand and enhance the existing hydrangea garden, and showcase the depth and breadth of these iconic plants for Heritage visitors.
Test garden partners include professional growers such as Bailey Nurseries and Ball Horticultural Company as well as Dr. Michael Dirr and his wife Bonnie, the Cape Cod Hydrangea Society and the American Hydrangea Society.