Best grown in rich, medium moisture, well-drained soils in part shade. Tolerates full sun only if grown with consistently moist soils. Soil pH affects the initial flower color (blue in highly acidic soils and lilac to pink in slightly acidic to alkaline soils). Add aluminum sulfate to the soil to make the initial flowers bluer or add lime to the soil to make the initial flowers pinker. Begin soil treatments well in advance of flowering. Prune after flowering by cutting back flowering stems to a pair of healthy buds. Prune out weak or winter-damaged stems in early spring. Can be grown in USDA Zone 5 with protection (e.g., mulch and burlap wrap), but may lose significant numbers of flower buds or die to the ground in harsh winters, thus respectively impairing or totally destroying the bloom for the coming year.
Big leaf hydrangea (H. microphylla) is a deciduous shrub with a rounded habit that, in the St. Louis area, typically grows 3-6’ tall and as wide unless damaged by harsh winters or pruned smaller. It generally features dark green, serrate, obovate to elliptic leaves (4-8” long) and large clusters of long-blooming summer flowers. Flowers appear in two types or groups: (1) LACECAP GROUP which features flattened flower clusters (corymbs) of small fertile florets with scattered showy sterile florets often forming a marginal ring, and (2) MOPHEAD OR HORTENSIA GROUP which features rounded, globose, mophead-like clusters (corymbs) of mostly showy sterile florets. ‘Homigo’ is a mophead-like cultivar that is noted for its changing flower colors. Flowers emerge as either pink or blue (depending on soil acidity), but as they mature change color first to light green and finally to red. In mid-summer, individual plants will often have flowers blooming in all three colors at the same time. Each mophead cluster typically grows 6-8” wide. Dark green, serrate, obovate to elliptic leaves (4-8” long). Blooms in July for up to two months.
No serious insect or disease problems. Some susceptibility to bud blight, bacterial wilt, leaf spot and mildew. Aphids are occasional visitors. Winter hardiness can be a problem in cold winters in the St. Louis area.
Group or mass in a sheltered location in the shrub border. Also a good specimen or accent for protected locations near homes or patios.