Getting the best native hydrangea for your garden
This nutsfornatives photo of hydrangea arborescens "Annabelle,' one of our three native hydrangeas, posted on Instagram last week prompted a question by Nature by Design, a jewel box of a nursery in Alexandria, Virginia that sells plants native to the Chesapeake watershed. The good folks there asked "what is the most telling difference between the native and the cultivar 'Annabelle'?" And the complexity of plants unfurls!
"Cultivar" comes from a 'cultivated variety.' The biology dictionary tells us cultivars are plants which can be distinguished from others by a characteristic that always remains true, such as a plant that self fertilizes. This is relevant to us lay person gardeners because the whole point of using native plants is to increase food available to insects which in turn allows the food chain to prosper and thrive.
Telling the difference between the straight species and the 'cultivar' Annabelle is important because the Annabelle is self fertile, so its flowers are mostly sterile, meaning they won't help pollinators as much as the straight species, hydrangea arborescens. You can see the difference in the flowers below. On the left, is the cultivar. On the right is the straight species which is a "lace cap" style flower. As I understand it, the portion of the bloom that is a petal is sterile. So, the flower on the right has fewer petals and more fertile flowers for pollinators.
That's why Nature by Design specializes in straight species plants. So why is that 'Annabelle' cultivar called a native? According to the Missouri Botanical Garden, it's a naturally occurring cultivar discovered growing in the wild and, so, native.
What I know for sure, is both the straight species and the cultivar 'Annabelle' are great shrubs with white blooms flowering in late spring and early summer. To maximize habitat benefit, though, go with the straight species, not the cultivar.
Hydrangea arborescens 'Annabelle' and hydrangea arborescens grow 4 to 5 feet high and wide. Both do well in shade or part shade and, like all hydrangeas, need moisture, particularly during the summer heat. These are also often called smooth hydrangeas. These hydrangeas bloom on new wood so it's ok to cut them back in fall through late winter.
Speaking of native hydrangeas, the third, and outstanding, native hydrangea, with no complexities as far as I am aware, is oakleaf hydrangea, also a late spring, early summer bloomer. The panicle flowers are incredible and these shrubs also have fabulous fall color, interesting bark in winter, and subtle spring interest as the minty green leaves unfurl. Oakleaf hydrangeas have a more informal shape and get quite large, up to 7 to 12 feet tall and wide. There are also smaller cultivars of oakleaf hydrangea. Oakleaf hydrangeas tend to grow better than the arborescens in sunnier spots. Oakleafs bloom on old wood so do not cut these back in fall or winter because you may remove next year's blooms.
All of our native hydrangeas have white flowers and look great in woodland gardens. The two arborescens types are perfect for more formal locations. Unlike Asian hydrangeas, you can't alter the bloom color of the flowers by making the soil more or less acidic. The natives are all easy to grow and are super reliable so long as they have moisture.
Happy hydrangea gardening.