Exploring Oakleaf Hydrangeas at Mt. Cuba
- Nuts for Natives
- Jul 9
- 4 min read
Checking in on a plant trial with native plant experts.
Mt. Cuba Center is a mecca for native plant gardeners. It's a treasure trove brimming with examples of how to use virtually every native plant in our region in formal gardens, english style borders, woodlands, surrounding a gorgeous pond, in meadows and in spaces in between,
If you haven't been recently, new additions include an outdoor gravel seating area amidst an allée of trees worthy of a Paris public garden. Choose a table and enjoy the shade beneath the umbrellas for a picnic. There is also a new welcome center for visitors with a small selection of robust native plants for sale. And the gardens - gorgeous as always!
I went to learn more about their trial gardens. This is the area where the Mt. Cuba team plants many, many varieties of a single plant, help get those plants established the first year and then step back to evaluate how the plant grows and how attractive the plant is to pollinators. At first, this may seem a bit esoteric for home gardeners but these trials are really important.
Listening to Sam Hoadley, Mt. Cuba's manager of horticultural research, talk about these trials, I realized how key they are to getting more people and landscapers to plant native plants. Sam talked in particular about results from the first several years of their oakleaf hydrangea (Hydrangea quercifolia) trial. Oakleaf hydrangeas are native to the southeast, so south of the Chesapeake Bay watershed. The shrubs grow well here, though, and are pretty mainstream plants in our landscapes. Since they are not native to the Chesapeake watershed, a lot of their ecological value is to generalist pollinators.
Sam explained it's really important for people to have good experiences with native plants so they will want to plant more. In the case of oakleaf hydrangeas, he says they are very adaptable and also widely available. Those were two important factors in choosing to trial oakleaf hydrangeas. There is no sense in trialing plants most people will not be able to find. The trials show us which of the many cultivars and straight species grow really well and attract more pollinators. This is good for the business of native plants! This information helps garden centers, garden designers, landscapers and homeowners have successful outcomes.
On to those oakleaf hydrangeas. Twenty-six different types of shrubs were planted in sun and eighteen of those were also planted in shade in 2021. Several years in, Sam noted some observations about which can best withstand wind, rain and sun. We looked at three types of oakleaf hydrangeas -- cultivars that grow to the size of the straight species (7 to 8 feet high and wide), cultivars bred to be smaller (4 to 5 feet high and wide) and the straight species. While the trial still has a year or two to go, Mt. Cuba is noting some observations so far:
larger hydrangeas with double flowers tend to flop and don't support pollinators as well because of all the sterile flowers
hydrangeas bred to be smaller sometimes end up with snub nosed flowers instead of the graceful panicles
some hydrangeas are very floppy and burn in full sun and some neither flop nor burn.
A Few of Mt. Cuba's Early Favorites
Oakleaf hydrangea 'Amethyst' is near the top of the list of larger shrubs for holding shape and color. "Amethyst' also has flowers with a healthy number of fertile flowers for pollinators. The fertile flowers are the small green little bud like structures and infertile flowers are those with the petals that give the panicle its white or pink color.
Oakleaf hydrangea 'Gatsby Pink'â„¢ is another of the larger shrubs near the top for the number of pollinators attracted. Sam notes these flowers hold their color longer than most. Of the smaller cultivars, oakleaf hydrangea 'Ruby Slippers' was noted for retaining the graceful shape of panicle flowers.
There are two straight species oakleafs in the trial. These are plants that have not been altered or bred for better traits. They were not as upright as some of the cultivars but the flowers were glorious. The straight species shrubs had no burned foliage and were fairly upright, though not as upright as some of the cultivars.
I came away with a much greater appreciation for these plant trials and a better understanding of how important they are. I would be so disappointed if someone gave a native shrub a try and and ended up with one of these scenarios. While you or I might figure out how to remedy this, someone just starting out with native plants might conclude it's a no go! Not exactly what we are aiming for.
Oakleaf Hydrangea Tips
As Sam talked about his experience growing the many oakleaf hydrangeas, he shared some helpful tips:
oakleaf hydrangeas bloom on old wood (the previous season's growth) so any pruning has the potential to eliminate flowers for the following growing season
older oakleaf hydrangeas can be cut back nearly to the ground to rejuvenate a plant but you would forgo all flowering for the following summer. March is the best time to do this
oakleaf hydrangeas don't like too much moisture. They are great for shaded woodlands and rocky slopes where they are often found in the wild
Spring is the best time to transplant these shrubs. They have both shallow fibrous roots and deeper roots and will take a year or two to reestablish after transplanting
Mt. Cuba tends to deadhead their oakleaf hydrangeas in March
The best news of all: these trial gardens are available to anyone who visits Mt. Cuba. Mt. Cuba has added signs in the trial garden identifying those plants trending towards the top as the trial continues. Visiting Mt. Cuba anytime during the growing season is an experience packed with inspiration no matter what type of gardens you like or, for that matter, whether you are even a gardener. Check out the visitor info, pack a picnic and make a day of it!
Happy Gardening.
