We live in in north Georgia, deep into the native range of this hydrangea species, so prefer to call Hydrangea arborescens by the common name wild hydrangea, as others do too. Books and the Internet call it smooth hydrangea more often than anything else.
When researching wildflowers, I've seen arborescens called American hydrangea. Though that name doesn't surface amongst hydrangea aficionados, who call it smooth hydrangea, like the books and web.
There's no simplicity to any hydrangea species and wild hydrangea is no exception. Let's wade into this particular hydrangea thicket together and figure out some of the eccentricities.
Where is arborescens native to? Sadly, not my backyard, but it is native to backyards in the Appalachian mountains. The range extends down into the foothills all around - from Pennsylvania to Alabama, heading further west to Arkansas/Missouri, and even south to the unique flora of the Florida panhandle.
As one of those plants that has a penchant for disturbed soils, arborescens can be spotted in summer all along roadsides and ditches in the Appalachians. This species likes forest edges and, incredibly, it finds purchase in rock crevices* of the mountains!
*Don't try this at home. Hydrangea arborescens, or any hydrangea, is not a rock garden plant. Honestly, I don't know how it happens to be happy in crevices, but I've seen plenty of pictures of this happening in wild locations in North Carolina and Virginia. It boggles the mind, even though it's in cool, moist climates where they are pulling this stunt.
Lacecap and Mopheads
Just like Hydrangea macrophylla (bigleaf hydrangea), H. serrata (mountain hydrangea), and viburnums, arborescens grows with both lacecap and mophead flower heads. They are not on the same bush, they occur on separate bushes.
In general, the lacecaps are the wild types because nature likes them better.
Learn more about Lacecaps ➞ What is a Lacecap Flower?
Why would nature have a preference? Because lacecaps have fertile florets in the center of each head that attract pollinators. Fertile flowers and pollinators mean seeds and the perpetuation of the species.
Green Dragon - Small lacecap florets, but it's desirable for the alluring cut leaves unlike any other hydrangea
Haas Halo - Giant lacecaps - the most charismatic arborescens lacecap; flowers are held on strong stems
Mopheads do occur in nature, but in general they are selected and bred by humans because they are more showy. The mopheads can get so big they border on the outrageous, the truly bodacious.
Grandiflora - One of the first mopheads, but by comparison with modern selections, these mopheads are puny
Annabelle - an old selection, but still one of the best. Nice big mopheads.
Balsam - these mopheads are Titans
Proven Winners has a line of white mopheads that are worthy, but they can be found in local garden centers so we don't fool with them.
Flowers, both mopheads and lacecaps, are white. They open green, when they are fertile at their peak they turn white, then the age back to green or cream, finally brown.
Color is not effected by soil pH, like it is for H. macrophylla, H. serrata, and Dichroa febrifuga.
The mopheads are excellent for harvesting dried flowers. I cut them when they are green or cream, before they hang around too long and turn brown.
Pink flowers are a new thing for this species. When I was first learning plants back in the 90s, the only pink form available was Eco Pink Puff and it was very modest: small flowers, pale pink, all fertile florets. Yet, it was pink so much-celebrated. A nice thing about it was all the fertile florets for pollinators. It's hard to find Eco Pink Puff nowadays because in the past decade or so pink mophead arborescens flowers became the quest of arborescens breeders.
So far, Proven Winners has provided gardeners with several beautiful pink types with strong stems that keep the flowers from flopping, particularly Invincibelle Spirit 2, Mini Mauvette, and Ruby. Please note the Invincibelle Spirit form with 2 in the name has stronger stems - it's like a reboot of the original Invincibelle Spirit, which flops. We don't sell any of the PW brand simple because they can be found easily at local garden centers. They are lovely and we do recommend them.
Size varies by cultivar, but arborescens is typically wider than tall, making it look like a massive muffin top with white dollops of frosting. I've seen a lot of 3 to 4' and 5 to 6' tall plants in gardens, though I've seen pictures of sweeps of large Annabelles that look to be easily reaching 8' tall.
Adding to the width is its colonizing nature. Yes, your bigleaf will layer branches, but this one colonizes. I say this too much, but it warrant repeating . . . colonizers are great at filling in an area and making sure the plant has a good foothold in that spot.
Sometimes the bushes can become so heavy laden with flowers that they flop. Many folks don't mind this at all and accept it as just the way it is.
There are three ways "fixers" can remedy the floppiness:
1) Breeders are working on selecting for strong stems to support significantly large or beautiful flowers, so look for cultivars with notable strong stems;
2) Prune to create a structure of strong stems;
3) Plant individual plants closer together than you normally would - the proximity to each other will support each other's stems.
The bark is nothing to sing about like that of Hydrangea quercifolia (oakleaf hydrangea), however it is significantly peeling and stringy. This quality has earned it the name sevenbark, I don't think for technical reasons of exfoliating in seven, rather for the lyricism.
Wild hydrangea excels in the cool and even cold climates of zones 3 to 7. So, if you want big white mopheads, but can't grow a macrophylla (bigleaf hydrangea) because you live in the colder regions, then grow arborescens! This species will give you undulating mounds of bodacious white mopheads every year. Every.
"Technically" arborescens will grow in zone 8. Though the shrub can be short lived. I have seen some old plants in zone 8a, but the gardener got lucky*, in my professional opinion. It is not a great lover of the hot summer nights of the Deep South.
*I do believe there is an element of luck in gardening, sometimes.
Because wild populations of arborescens can be found in the Florida panhandle (!), it is considered a zone 8b plant. Growing in zone 8b is an anomaly.
Did you know that there are other anomalous plant populations in the panhandle? Either oddballs follow the waterways down and stick to river banks (like Kalmia latifolia - mountain laurel) or there are disjunct populations pushed down by glaciers (like Aquilegia canadensis - columbine). The waterway species and the species geographically separated from their main populations are growing quite happily in the panhandle. I don't know how well gardeners fare with these species - I would guess that unless seeds are sourced from those endemic populations, it would be hard to grow a columbine grown from seed from a northern location.
Back to arborescens care and culture. In the north, full sun will be fine, but in the south, morning sun turning into afternoon shade is the best situation.
Flowering profusion is, as with most hydrangea species, best if the plants receive at least morning sun.
Watering is tricky. It tends to dramatically wilt like a macrophylla during the hot afternoons of zone 8a. Yet, it doesn't like to be overwatered. Once established, don't water them as much as you water your macs.
Also, in our nursery, we found this species doesn't love our cold wet winters, just like H. serrata (mountain hydrangea) doesn't love them. So we cover both serrata and arborescens during long wet spells, to control the amount of water they receive, especially during the winter.
Hydrangea arborescens has the most common names of any hydrangea. We've already covered smooth hydrangea, wild hydrangea, American hydrangea, and sevenbark, but there's one more. It's Annabelle hydrangea - sort of an eponymous name applied because the cultivar Annabelle has become the most common type. Annabelle is so popular and well-known that gardeners have started calling all smooth hydrangeas by that name, Annabelle hydrangea.
So, if you are looking for an Annabelle hydrangea, but aren't specifically talking about that cultivar, then you've found the right plant in the wild smooth American hydrangea.
Happy Hydrangeaing (is that a word?),
Hillary & Mike