Hydrangea quercifolia—Oakleaf Hydrangea
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, Master Gardeners rarely suggest hydrangeas as suitable garden choices since these vigorous, shade-loving shrubs with large, dramatic blooms are generally much more appropriate for climates with humid air and summer rains. However, there is one notable exception: Hydrangea quercifolia, the oakleaf hydrangea. Unlike the mophead and lacecap species, it not only thrives in our climate but is a stunning garden specimen. This is the single hydrangea on our list of Recommended Plants for Sonoma County.
H. quercifolia, native to the Southeastern United States, is so named because its leaves are deeply lobed, resembling those of the northern red oak (Quercus rubra). Leaves of other hydrangeas are not lobed, and the difference doesn’t stop there. Leaves of H. quercifolia are also thick, coarse, sparsely serrated with downy white undersides and bristled with tiny hairs. 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.
Oakleaf hydrangeas generally grow to about 6-7 ft. tall at maturity and about 7-8 ft. wide in 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 others in the genus but they can also grow in a range of exposures from full sun to full shade; dappled shade is ideal. Inland, plants require more shade; closer to the coast, the more sun they will tolerate.
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. Like other hydrangeas, all parts are slightly toxic if ingested.
Grown primarily for its white, conical summer flowers that can reach almost a foot in length, oakleaf hydrangea doesn’t quit there. As many summer-flowering shrubs wither and drop their leaves, oakleaf hydrangea foliage puts on a fall coat of glorious, showy color, ranging from red to purple to bronze.
Technically deciduous, it holds its leaves into early winter. When they drop, the bare shrub showcases its rusty, peeling branches and stems. Old stems have a shredded, cinnamon-colored bark that provides winter interest, evocative of manzanita and Arbutus. In spring, new growth emerges in striking color and texture covered with soft, silky hairs.
H. quercifolia can be grown as a specimen, in small groupings, or as part of a landscape border. Some 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—some reach 15 ft. and should be chosen with care. ‘Snowflake’ is a popular choice, although the flowers are a bit heavy; ‘Pee Wee’ and ‘Sikes Dwarf’ are recommended for smaller gardens, as they are in the 4-6 ft. range. ‘Munchkin’ stays at 3 ft. high and wide.