Hydrangea is a genus of about 70 to 75 species of flowering plants native to southern and eastern Asia (China, Japan, Korea, the Himalayas, and Indonesia) and North and South America. By far the greatest species diversity is in eastern Asia, notably China, Japan, and Korea.
Most are shrubs 1 to 3 meters tall, but some are small trees, and others climbers reaching up to 30 metres by climbing up trees. They can be either deciduous or evergreen, though the widely cultivated temperate species are all deciduous. Hydrangeas are popular ornamental plants, grown for their large flowerheads, with Hydrangea macrophylla being by far the most widely grown with over 600 named cultivars.
There are two flower arrangements in hydrangeas. Mophead flowers are large round flowerheads resembling pom-poms or, as the name implies, the head of a mop. In contrast, lacecap flowers bear round, flat flowerheads with a center core of subdued, fertile flowers surrounded by outer rings of showy, sterile flowers. These flowers are produced from early spring to late autumn; they grow in flowerheads (corymbs or panicles) at the ends of the stems.
Some Hydrangeas are best pruned on an annual basis when the new leaf buds begin to appear. If not pruned regularly, the bush will become very ‘leggy’, growing upwards until the weight of the stems is greater than their strength, at which point the stems will sag down to the ground and possibly break. Other species only flower on ‘old wood’. Thus new wood resulting from pruning will not produce flowers until the following season.
In Japan, ama-cha, meaning sweet tea, is an herbal tea made from Hydrangea serrata, whose leaves contain a substance that develops a sweet taste (phyllodulcin). For the fullest taste, fresh leaves are crumpled, steamed, and dried, yielding dark brown tea leaves. Ama-cha is mainly used for kan-butsu-e (the Buddha bathing ceremony) on April 8 every year—the day thought to be Buddha’s birthday in Japan. Ama-cha is poured over a statue of Buddha in the ceremony and served to people in attendance. A legend has it that on the day Buddha was born, nine dragons poured Amrita over him; ama-cha is substituted for Amrita in Japan.
Hydrangeas are moderately toxic if eaten, with all parts of the plant containing cyanogenic glycosides. Hydrangea paniculata is reportedly sometimes smoked as an intoxicant, despite the danger of illness and/or death due to the cyanide.