With around 300 hydrangeas in the garden, and fifty other members of the hydrangea family (Hydrangeaceae), Heronswood is hydrangea central. We celebrate this love affair with an annual event, the Hydrangea Festival, early in August. Bringing together hydrangea growers, floral designers, and fans of these fabulous flowers, the Festival highlights the great diversity of Hydrangea and the many great garden plants to be found in its family.

As currently construed, the Hydrangeaceae includes nine genera with only two species native here in Washington State: mock orange (Philadelphus lewisii) and yerba-de-selva (Whipplea modesta). The family is broken down into two subfamilies: Jamesioideae (Jamesia and Fendlera) and Hydrangeoideae (everything else). The latter is then split into two tribes: Hydrangeae (Hydrangea only) and Philadelpheae (Philadelphus, Carpenteria, Deutzia, Kirengeshoma, Whipplea, Fendlerella). Some gardeners are surprised to discover that that mock orange and kin are related to hydrangeas, but they share characteristics such as opposite leaves and flowers with four petals (mostly).

Hydrangea itself has just under 100 species of shrubs, herbs and vines. It now includes eight other genera (Broussasia, Cardiandra, Decumaria, Deinanthe, Dichroa, Pileostegia, Platycrater, Schizophragma) that were until recently considered separate. The U.S. has five native species of Hydrangea, but none reach farther west than Oklahoma. Most wild hydrangeas occur in Asia and South America, with none in Europe, Africa, or Australia. In cultivation, there are thousands of hydrangea cultivars, greatly exceeding the number of wild species. These were selected from particularly good wild forms or produced via cross breeding. The most important hydrangea species in cultivation are H. macrophylla (big-leaf hydrangea), H. serrata (mountain hydrangea), H. paniculata (panicle hydrangea), H. quercifolia (oak-leaf hydrangea), H. arborescens (smooth hydrangea), and H. aspera.