Hydrangea Pollinator Madness
6/27/2023 5:07 pm
Two native Hydrangeas stand out as pollinator favorites. Our native oakleaf hydrangea (Hydrangea quercifolia) is literally abuzz from May through June, vibrating with visitors. A few weeks later, as the oakleafs begin to fade in scent, Hydrangea arborescens (wild hydrangea) takes center stage.
Oakleaf hydrangeas come in a wide range of sizes now and feature more pink and red tones than ever. Hydrangea quercifolia 'Alice' is a large cultivar (8-10+ feet) that in cooler years changes from white to a beautiful shade of soft pink. As someone allergic to bees, I admit I keep my distance from 'Alice' during much of its prime time. The air literally thrums with the sounds of visitors, mostly bees, wasps and some flies too. [Fun fact: 'Alice' was selected from a seedling on the UGA campus by Dr. Dirr and was named for a former horticulture student and research technician.]
Hydrangea quercifolia 'Alice'
'Alice' takes up a lot of ground, but fortunately there is now an oakleaf hydrangea sized for every garden. Consider these cultivars in descending size: 'Snowflake,' 'Snow Queen,' 'Ruby Slippers' and the oddly proportioned 'Munchkin' pictured below.
Hydrangea quercifolia 'Munchkin'
That said, not all oakleafs are created equal. You'd be hard pressed to find a pollinator on Hydrangea quercifolia 'Vaughn's Lillie'. Its double blooms are so dense, they are rarely penetrated by a pollinator and the least bit of rain sends them crashing to the ground. I confess I would probably not plant it again unless I was into cut flowers.
Hydrangea quercifolia 'Vaughn's Lillie'
Which leads us to the question -- what makes a Hydrangea a good pollinator? The difference is sterile flowers versus fertile flowers. Sterile flowers are the pretty petaled ones -- think bigleaf mophead flowers, whereas fertile flowers look like buds that never opened. Its the fertile flowers that hold the food the pollinators are after. On most oakleaf hydrangeas (except the dense Vaughn's Lillie), there is a great deal of space to get beneath the sterile blooms to the fertile flowers.
This explains why bigleaf mopheads are generally terrible for pollinators. They have few fertile flowers and what ones they have are difficult to reach. Lacecaps (a subgroup of mopheads), and Hydrangea serrata are much better for pollinators, as are "wild hydrangeas" -- Hydrangea arborescens, all having many fertile flowers. That said, even in the H. arborescens family there is much variation in fertile to sterile flower proportions.
One look at Hydrangea arborescens 'Haas Halo' quickly reveals why this is the champion pollinator plant for the species. A vast quantity of fertile flowers lie quite flat and accessible. Just like Hydrangea quercifolia 'Alice', this cultivar of the native H. arborescens in bloom is like a small city feeding bees and wasps. The flower heads are very flat and can reach 12" wide. It's a bit of a strange looking plant, but it never flops as do many arborescens (particularly Annabelle). It also gets quite tall, so a periodic pruning back to 3 or 4' tall is fine, with the cost being somewhat less wide blooms. And unlike Annabelle, no deer has yet to touch this one (knock wood).
Hydrangea arborescens 'Haas Halo'
Not all H. arborescens are winners at attracting pollinators, however. 'Annabelle' is so-so at attracting pollinators in my garden, although Mt. Cuba gives it good ratings. Maybe the abundance of easier feeding hydrangeas on my property explains the discrepancy? Riffs on 'Annabelle' like 'Invincibelle' and 'Incrediball' are also marked as top performers for pollinators. Let us know your experiences. Email us.
So if you want to bring in the pollinators, know you won't fare poorly with oakleaf and wild hydrangeas if you skip the very dense blooming ones full of sterile flowers. Pollinators prefer not to work extra hard for their food, much like humans.
Contributed by Liane Schleifer
Note: If you find yourself looking for assessments of native and native cultivar (nativar) pollinator plants, remember to check out Mt. Cuba Center's trial garden reports. Mt. Cuba Trial Reports. These studies are limited to natives and nativars, so they won't tell you anything about pollinator activity on non-natives. Also, read the fine print carefully. Even though the number counts of insect visits to a plant may vary noticeably to your eye, often there is no meaningful statistical difference, a fact that is disclosed in the plant report elsewhere.