Hydrangea is a genus of about 23 species native to Asia and the Americas. Hydrangeas are widely grown in both home and commercial landscapes and are one of the most economically important nursery crops in the US. With its display of showy pink or blue flowers and bold foliage, H. macrophylla (bigleaf hydrangea), is the most popular. Other ornamental species include H. arborescens (smooth hydrangea), H. quercifolia (oakleaf hydrangea), H. serrata (serrated hydrangea), and H. paniculata (panicle hydrangea). Hydrangeas are generally trouble free, but powdery mildew can be common in some species later in the growing season.