Hydrangeas make a statement in the landscape with their lushly textured leaves and showy blooms. Although hydrangeas are thought of as a flower for warm, Southern climates, several varieties are well adapted to Northern gardens. Keep hydrangeas healthy by mimicking their native woodland surroundings -- dappled shade and cool, moist soil, well amended with peat moss or compost. Given proper care, your ailing hydrangea will probably recover.
Water the soil to keep it evenly moist, but not soggy. The word hydrangea comes from the Greek "hydra" meaning "water" and "angeon" meaning "vessel," indicating the plant's preference for moist, cool soils. Spread a 2-inch wood chip mulch around the base of the plant to conserve moisture.
Cut back the hydrangea to 12 inches high and replant it in a location receiving some morning sun but partial afternoon shade. If you live in a hot climate, your hydrangea may require even more shade. Bright sunlight causes the plant to droop and scorches the leaves. Drying winds damage hydrangeas. Select a site protected by a wall or other shrubs.
Remove and discard dead or diseased leaves and stems. Hydrangeas are susceptible to several diseases, such as leaf blight and powdery mildew, but these diseases are rarely life threatening, according to the Auburn University Extension. Watering early in the morning or using drip irrigation helps prevent disease. Space your plants so they receive plenty of air circulation. If the disease is severe, contact a local nursery specialist to positively identify it and recommend a treatment, such as a fungicide spray.
Your hydrangea may be dying because it is not well suited to your climate. Bigleaf hydrangea thrives in U.S. Department of Agriculture Plant Hardiness Zones 6 to 9. In zones north of Zone 6, the plant will likely suffer frost damage or may be killed outright. Try panicle hydrangea, smooth hydrangea or climbing hydrangea varieties if you live in a cold climate. If you transplant your hydrangea, do it on a cool, cloudy day in the evening or early morning. The best times to plant hydrangeas is in the fall or early spring. Give transplanted hydrangeas plenty of water and a diluted vitamin B-1 starter supplement to minimise transplant shock.