Answer: It sounds as though your hydrangeas are quite stressed so something isn't quite right with their growing environment. Here are a few pointers for growing hydrangeas:
Hydrangeas are susceptible to leaf spots, blights, wilts and powdery mildew. Insect pests on hydrangea include aphids, leaf tiers, rose chafers, oyster scale and red spider mites. These pests are uncommon and if seen may be a sign of another problem causing plant stress. Powdery mildew is common on some varieties, but is rarely life threatening.
Hydrangeas are relatively easy to grow in well-drained soils containing plenty of organic matter. They, like most Southeners, prefer warm, morning sun and cooler, afternoon shade. Avoid planting in hot, dry, exposed sites. Buying any Hydrangea during bloom does help to verify variety and flower form, but the best time to plant them is actually fall. Early spring is the next best planting time. With extra care, they can be planted at other times.
Dig the planting hole two feet wider than the plant's root ball and only as deep as the root ball. In heavy soils, consider preparing a planting bed instead. Amend with compost to create a mound for planting. Planting high on a mound allows better drainage for roots.
While many Hydrangeas benefit from shade, planting any shrub under a large, established tree is a tough situation. Large trees require and consume enormous amounts of water during the growing season. Newly planted shrubs often cannot compete successfully in this location. The gardener is then hard-pressed to supplement the needs of the new shrub.
To look and perform their best, Bigleaf and Smooth Hydrangeas need more water than do their relatives. Becoming tattered in appearance during periods of drought, they still survive only to need minor pruning to restore their form. The large, soft leaves lose water quickly and the hot sun wilts them. Well watered plants may still appear wilted if too much sun (or heat) is the added problem. Afternoon shade is a must for both these hydrangeas. One inch of water per week either by rainfall or irrigation is recommended, and of course, mulching helps conserve water loss and cool the root system.
Different Hydrangeas have different fertility needs. Bigleaf hydrangea responds to several light fertilizer applications during the growing season. A general-purpose fertilizer, such as 12-4-8, 16-4-8 or 10-10-10** applied in March, May and July is suggested (one pound per 100 square feet, divided applications). Panicle and Oakleaf Hydrangeas benefit from an April and June application of the same rate divided twice, while Smooth Hydrangea needs just one application in late winter. It is not necessary to remove the mulch when fertilizing, but water soon after application to help dissolve fertilizer into the soil.
Make sure the growing conditions are right for your hydrangeas and that they have good air circulation all around. Prune off any affected plant parts and remove them from the garden. Periodically hose your plants off to discourage insect pests. If you do this regularly, your hydrangeas should rebound and become beautiful and healthy specimens. Enjoy!
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