By Sam Hoadley and Laura Reilly
From naturalistic to formal, native hydrangeas find themselves used in a variety of garden settings. Our latest trial report has a hydrangea for everyone amongst the three species and 26 cultivars included in our five-year evaluation. There are even a few wild hydrangea cultivars (like Hydrangea arborescens Invincibelle® Wee White) that are so compact that they would be well suited for container gardens on a porch or patio.
We’re calling out a few of our favorite species and cultivars, all of which can be seen in Mt. Cuba’s display gardens beginning this April.
Hydrangea arborescens ‘Haas’ Halo’ is the top performer in our hydrangea trial. It’s overflowing with desirable ornamental qualities — including great vigor, massive flower heads, and good sun tolerance. This selection of wild hydrangea is also very popular with pollinating insects. ‘Haas’ Halo’ is a shrub that can be seamlessly incorporated into almost any garden design and we recently planted it in Mt. Cuba Center’s newest garden, the Woodland Glade. This new planting also includes another top hydrangea, H. arborescens ‘Mary Nell’. ‘Mary Nell’ is similar to ‘Haas’ Halo’ but features a double ring of sterile flowers which lights up shaded gardens and adds pizazz without compromising pollinator value. ‘Mary Nell’ is less sun-tolerant than ‘Haas’ Halo’ and unfortunately is rarely commercially available.
Of the pink-flowering wild hydrangeas, Hydrangea arborescens Incrediball® Blush is our favorite. The floral display of this cultivar is truly one of the best in the trial. The large rosy pink flower heads of Incrediball® Blush make a stunning addition to any garden. Over five years it remained relatively compact, reaching about 4’ tall and 5’ wide, making this a great option for smaller landscapes. While most wild hydrangeas in the evaluation performed best when grown in shade, several pink-flowering cultivars, including Incrediball® Blush, actually preferred full sun. We chose Incrediball® Blush for the new Upper Allee planting in the formal gardens adjacent to the main house.
Hydrangea radiata, or silver-leaf hydrangea is one of our favorite hydrangeas in the naturalistic gardens at Mt. Cuba. When grown in some shade, the ornamental qualities of H. radiata really shine. The silver undersides of the leaves, for which this species gets its common name, shimmer in the slightest breeze. The lacecap inflorescences edged with oversized sterile flowers add beauty in the landscape and value for pollinators in June and July. This species is used extensively in our gardens and can be seen in spectacular mass plantings in our entrance gardens and along the main drive. The one caveat associated with H. radiata and its cultivars is that they are the first hydrangeas in the trial to show signs of heat and drought stress and often exhibit significant foliage burn and premature leaf drop by late summer. This species could not be recommended for Mid-Atlantic gardens that receive full sun but would be right at home if planted in part sun to shade. While silver-leaf hydrangea is not as popular at garden centers as some of the more recent cultivars of wild hydrangea, Hydrangea radiata can be sourced from specialty mail order nurseries.
This spring, the wild hydrangea trial will be replaced with our second shrub trial, oakleaf hydrangeas! We are very excited to study another of North America’s native hydrangeas. This trial will be unique in that, for the first time, we are trialing a single species and comparing its many cultivated forms. Hydrangea quercifolia is a species with many seasons of interest. It is well known for the oak-shaped leaves for which it is named, white to pink panicle inflorescences in summer, incredible burgundy fall color, and exfoliating cinnamon-colored bark that can be admired during winter months. The trial will assess tried-and-true garden classics as well as a handful of newcomers to the horticultural market. The oakleaf hydrangea trial will be sited in full sun, however most of the subjects will also be grown under our shade structure for comparison. This will be an interesting trial for observing pollinator preference, as the percentage of fertile flowers per inflorescence in cultivated forms and selections of this species is quite variable.
If you didn’t get a chance to see the wild hydrangea trial in person, it’s not too late! Although the bulk of the wild hydrangeas will be rotating out of the Trial Garden to make way for the new oakleaf hydrangea trial, the top-performing shrubs can still be found in the Trial Garden for reference purposes. We look forward to seeing you this spring and sharing with you the beginnings of our newest trial!
For more information check out our Wild Hydrangea Research Report.