By Sara Malone, Sonoma County Master Gardener
Hydrangeas are shrubs whose name derives from the Greek words for ‘water’ (hydor) and ‘vessel’ (angos), supposedly because of their love of water and the shape of their seed pods. In Sonoma County we don’t see many hydrangeas and we Master Gardeners rarely suggest them as suitable garden choices here. These vigorous, shade-loving shrubs with the large, dramatic blooms are generally much more appropriate for climates with humid air and summer rains. However, there is one notable exception: Hydrangea quercifolia, which not only thrives in our climate but is a stunning garden specimen! This is the only hydrangea on our list of ‘Top Plants for Sonoma County’.
H. quercifolia is so named because its leaves are deeply lobed, resembling those of the Northern Red Oak (Quercus rubra) and is native to the Southeastern United States. The leaves of the rest of the hydrangea genus are not lobed, and the difference doesn’t stop there. H. quercifolia’s leaves are also thick , coarse, serrated and bristled with tiny hairs, with downy white undersides. The thickness and pubescence (hairiness) aid in the plant’s moisture retention and make it the one hydrangea that can coexist happily in our gardens with low-water Mediterranean and California Native plants.
Oak leaf hydrangeas generally grow to about 6-7’ tall at maturity, and to about 7’-8’ wide. They have a pleasing mounding habit that is less stylized than the round, more formal shape of their cousins in the genus. Not only do they require less water than the rest of the family but they can also grow in a range of exposures from full sun to full shade, depending on your microclimate. Here in Petaluma I have mine in half shade/half sun and in dappled shade. The further inland you are, the more shade that they will require; the closer to the coast, the more sun they will tolerate. They are said to prefer a slightly acidic soil but they seem to thrive with the regular compost amending that I do without any special treatment to lower the pH.
H. quercifolia has no known disease or pest problems and is a fairly slow grower, especially when compared to other hydrangeas. This makes it a well-behaved garden citizen that can be counted on not to demand too much care or water. However, the best thing about H. quercifolia is the display that it puts on all year round!
Grown primarily for its white, conical summer flowers that can reach almost a foot in length, oak leaf hydrangea doesn’t quit there. True, the flowers are stunning and long lasting and fade to soft, rusty pink as they age. However, my favorite season for this hydrangea is autumn. Right now, as many summer-flowering shrubs are withering and dropping their leaves, oak leaf hydrangea is putting on a fall coat of glorious, showy color, ranging from red to purple to bronze. It is technically deciduous, but it holds its leaves into early winter, and when they drop, the bare shrub showcases its rusty, peeling branches and stems. Old stems have a peeling cinnamon-colored bark that is evocative of manzanita and Arbutus and provides winter interest. In spring the new growth is covered with soft, silky hairs with striking color and texture.
H. quercifolia can be grown as a specimen, in small groupings or as part of a landscape border. Some local wineries and large gardens use it in mass plantings as well. There are named varieties that are said to improve upon flower size and shape and produce larger plants (be careful – some of them reach 15’). ‘Snowflake’ is a popular choice, although the flowers are a bit heavy for my taste, and ‘Pee Wee’ and ‘Sikes Dwarf’ are recommended for smaller gardens, as they stay in the 4-6’ range.
Oak leaf hydrangeas are readily available at most nurseries around the County.
©Sonoma County Master Gardeners