The genus Hydrangea contains around 70 species which are native to Asia and the Americas. The most diversity exists in eastern Asia in Korea, China, and Japan. The name Hydrangea comes from the Greek word hydriai, meaning water vessel, due to the resemblance of the seed capsules to a water vessel.
Culture for Hydrangea
Some species of Hydrangea (H. macrophylla, H. paniculta) are shrub species where others are better suited to climbing. Most Hydrangea are deciduous and frost hardy. Full and partial sun is preferred as plants in deep shade are unlikely to bloom. "Mophead" and "Lacecap" cultivars of H. macrophylla (amongst others) can change flower colour depending on soil pH due to the availability of aluminium. Thus a flower in a more acidic soil (4.5 to 5) will tend to be blue, whereas in more alkaline soils (6 to 6.5) flowers will tend to be pink/red. Nevertheless, all Hydrangea species have a similar range of conditions and can tolerate sand, clay, and loamy soil types providing they are well drained. Although little formative pruning is required, all species respond well to, and produce better flowers if they are cut back to the lowest pair of buds in early mid spring.
Concerns about Hydrangea
Hydrangea can be affected by powdery mildew, particularly "Mophead" cultivars, Grey mould (Botrytis cinerea), and Armillaria root rot, particularly H. quercifolia. Other pests are vine weevil, hydrangea scale, aphids, and capsid bug.
Management Practices for Hydrangea
Early mid April to late May sprays of insecticides/fungicides can be implemented to control scale/scab. Three sprays need to be applied. Winter wash (Nov to Feb) to prevent infection. Check soil for nutrient imbalances/unsuitable conditions. If Honey Fungus is present, use RCX and application of biological controls at the first sign of symptoms to help control infection.