The lustrous, green foliage of the hydrangea is a highlight of the species for many gardeners. Set off by showy flowers, the leaves of a hydrangea can be sensitive and the plants can demand diligent attention, including a proper supply of water and fertilization. Various diseases also attack the leaves of the shrub.
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Hydrangeas are flowering shrubs that require moist, well-drained soil in order to thrive. When hydrangea leaves are dry and curling, the most likely cause is drought or insufficient watering. Hydrangeas' need for sufficient water is hinted at in the Greek origin of its name; "hydra" translates to "water" and "angeon" means "vessel." The shrub appreciates partial shade, as a full onslaught of sunshine causes the leaves to dry and droop, and the flowers to scorch.
Hydrangeas offer bright color in the garden from summer through fall, and placement of mulch around the shrub can help to retain moisture in the earth and minimize the possibility of hydrangea leaves curling and becoming dry. Testing the soil to determine whether fertilizer is necessary ensures the proper delivery of nutrients to the leaves and reduces the likelihood of the foliage losing vigor. Different species of hydrangea demand different levels of fertilization for optimal health.
Sensitive Hydrangea Species
The Bigleaf, or French, hydrangea (Hydrangea macrophylla) and the Smooth hydrangea (Hydrangea arborescens) require more water than other hydrangea species. Their delicate, large leaves suffer water loss rapidly and they thrive best when supplied with at least 1 inch of water weekly, whether through rainfall or irrigation, especially during periods of hot, dry weather. The Bigleaf hydrangea is also more sensitive to leaf damage from early or late freezes or surprise frost.
Hydrangea Leaf Diseases
Powdery mildew, leaf spot and root rots affect the leaves of a hydrangea detrimentally. Neither powdery mildew nor Cercospora leaf spot are likely to kill the plant, but extreme attack by the Cercospora fungus is likely to lead to a drying and curling of leaves, followed by defoliation. The fungus remains in the fallen leaves and spreads easily to adjacent plants. Meanwhile, a soil-borne fungus, Armillaria root rot, eats away at the roots of a hydrangea, preventing them from supplying water and nutrition to the hydrangea leaves.