Caring for Hydrangea

Hydrangeas have high water needs and suffer quickly in dry soil, especially during summer. Water deeply two or three times a week in warm weather, more often if planted in a container or free-draining ground. In spring and autumn, once a week is usually sufficient if rainfall is average, but check that the top few centimetres of soil don't dry out. Mulch annually in early spring with a 5 cm layer of composted bark, leaf mould, or well-rotted manure to lock in moisture and suppress weeds. Feed in March or early April with a balanced slow-release fertiliser such as blood, fish and bone, scattering a handful around the base of each plant and watering in. Give a second feed in June to support flowering. If you want blue flowers, your soil must be acidic (pH below 6); on neutral or alkaline soils, hydrangeas turn pink. You can encourage blue tones by applying a specialist hydrangea colourant (aluminium sulphate) in spring, but this only works if the soil pH allows it. Hydrangeas are hardy in zones 5b–9b, but late frosts can damage emerging buds. In colder gardens, consider planting in a sheltered spot or leaving old flowerheads on over winter for protection. No special winter wrapping is needed in most of temperate Europe. Watch for powdery mildew in dry summers, especially on plants in too much sun or with poor air circulation—improve spacing and water consistently. Aphids occasionally cluster on soft new growth in spring; a strong jet of water usually dislodges them. Capsid bugs can cause tattered holes in leaves but rarely warrant treatment. Yellowing leaves (chlorosis) often indicate alkaline soil; apply ericaceous fertiliser or sulphur chips to lower pH gradually.