Answer: What you describe is odd behavior for a hydrangea. There are no diseases common to hydrangea that would cause the plant to die from the top down so I would rule out diseases. It is more likely that your hydrangea is suffering some stress at the root level; poorly draining soil can suffocate the roots. Daily watering can speed the process along. Hydrangeas appreciate regular watering, but the soil should be allow to dry out somewhat between waterings. If you didn't dig a watering basin beneath your hydrangeas when you planted them, you might do so now. A water ring, sometimes called a water well, is a mound of compacted soil that is built around the circumference of a planting hole once a plant has been installed. The water ring helps to direct water to the outer edges of a planting hole, encouraging new roots to grow outward, in search of moisture. The height of the mound of soil will vary from a couple of inches for 3 gallon shrubs, to almost a foot for balled and burlapped trees, especially those planted on a slope. Mulch over the ring will help to further conserve moisture and prevent deterioration of the ring itself. To water properly, fill the water ring, allow to drain, then fill it a second time. Do this once a week (twice a week if weather is really hot).
If your plant doesn't improve, take a sample of the affected leaves and stem to your local Cooperative Extension office or nursery for positive diagnosis.
Best wishes with your hydrangeas.
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