Which ones do pollinators love best?
There are a lot of hydrangeas to choose from at garden centers. Lace caps, mop heads, panicles with blue, white, and pink flowers and combinations thereof. Our two native hydrangeas are the oak leaf (Hydrangea quercifolia) and the wild hydrangea (Hydrangea arborescens), both with white flowers. Oakleaf hydrangeas are native to the southeastern US. Wild hydrangeas are native to our area. Of the wild hydrangeas, some are lace caps and some are mopheads.
Mt. Cuba Center recently took a five year look at the native wild hydrangea and its many cultivars. In their report, Mt. Cuba studied 29 wild hydrangeas, the straight species and 26 of its cultivars as well as two native hydrangea from further locales.
The straight species is typically the plant you find growing in nature. Cultivars are crosses between the straight species and other plants with traits breeders believe will improve the original. Scientists tell us cultivars of native plants are probably ecologically ok so long as they don't change the color of the foliage or the style of the flower. They also say this is an area still being explored.
Here are some take aways for us home gardeners from all of the fantastic work by Mt. Cuba.
Hydrangea flowers have fertile and sterile petals
The flowers with petals are sterile whereas those without are fertile. The cultivar of the wild hydrangea above is very popular in garden centers because of its large number of mop head flowers shown below. In the Mt. Cuba trial, it was fifth from the bottom for attracting pollinators, likely because of the large number of sterile flowers says Mt. Cuba.
The native wild hydrangea was the 2nd most popular for attracting pollinators!
Second best? Yep. The first most popular for attracting pollinators was the cultivar of the wild hydrangea called 'Haas' Halo.' Why? Mt. Cuba found this cultivar has unusually large flower heads and so offers more fertile flowers for the bees, beetles and flies that like hydrangeas. Pollinators also strongly prefer lace caps over mop heads.
The only challenge with 'Haas Halo' is it's not readily available at local nurseries and garden centers or on-line right now. Good news -- number two in the line-up, the straight species wild hydrangea is available at a number of native plant nurseries like Watermark Woods in Loudon County in northern Virginia, Herring Run Nursery in Baltimore and Kollar Nursery in northern Maryland among others.
Hydrangeas can grow in full sun
Mt. Cuba grew each type of hydrangea trialed in full sun and almost all of them in shade as well to compare their growth. While Mt. Cuba concludes wild hydrangeas generally do best in shade; they can be grown in sun. Gives a bit of license to try a hydrangea even if you don't have a shady spot. The other thing I learned about the wild hydrangea is its staying power. The photo above in October shows the architectural interest that the plant still has late in the season.
It's not necessary to cut wild hydrangea back in the spring
Conventional pruning advice for hydrangeas that bloom on new growth as the wild hydrangea does, is to cut stems back to 8" or so in early spring to help reduce floppiness. Mt. Cuba says not so. Cutting them back does keep the shrub slightly smaller in size and encourage larger flowers but it does not reduce floppiness. Mt. Cuba advises cutting back a few of the oldest stems to the ground each year to ensure the plant has fresh growth.
Favorite take away!
Mt. Cuba found native bees colonizing in hydrangea stems that had been cut back. They apparently eat out the pith in the center of the stem and climb in to nest. For this reason, Mt. Cuba recommends bundling any stems you cut back and placing them around the garden to supplement habitat. The picture on page 17 of the report is worth a thousand words!
This report is loaded with information and photos about all of the wild hydrangea cultivars and tips on propagating too. If you are, indeed, wild for hydrangeas, you will want to check it out!
Thanks for gardening for the Chesapeake!