Overwatered hydrangeas can struggle with fungal diseases, including root rot which can lead to plant death. Allow your hydrangea time to dry out before you water again. If you feel that your soil may be too dense for your hydrangea, add compost to your heavy soil to lighten it up.
Water them for longer.
If you notice that your hydrangeas are starting to look stressed, de Corral says to try and shift your watering schedule to less frequent one, but with longer intervals.
The reason for a dying hydrangea is usually because the soil is too dry or the hydrangea is in too much direct sunlight which causes the leaves to turn brown, wilt and die. New growth in Spring is sensitive to frost damage which causes the leaves and flower buds to turn brown and mushy with a dying appearance.
Hydrangeas need regular water to thrive. Too little water can result in stunted growth and failure to develop flower buds. A drought in the previous growing season can also affect flowering the following year. Plants need consistent moisture, about 2 inches of water per week.
Prune back stems to just above a fat bud — called a heading cut — in fall, late winter or spring. These plants have conical-shaped flower heads. I recommend leaving the dry, tan flower heads on the plant to provide some winter interest in your landscape, so I wait to prune these until late winter or spring.
To rejuvenate the hydrangea, remove up to 1/3 of the older living stems down to the ground each summer. This will revitalize the plant. If necessary to control the size of the plant, cut back before late July to allow for buds to develop. Usually the plant will return immediately to its former size.
Brown, tan, yellowish or black spots on hydrangea leaves may be anthracnose. You can also identify it by cankers that form on stems and branches. Anthracnose can be fatal to hydrangeas, so prune out dead or diseased plant parts and destroy them.
You can use vinegar to lower the pH of your soil, but be aware that in order to achieve blue blooms, you will need both an acidic environment and aluminum ions. The acidic environment will also need to be a sustained over a period of time, which could be hard if rainwater is washing the vinegar away.
Here's what to look for: Leaf discoloration: hydrangea laves typically become yellow and brown when overwatered. However, the discoloration can also be a sign of underwatering. Usually, when the plant is overwatered, the browning occurs on the edges of the leaves.
In addition to bolstering future blooms and strengthening stems, deadheading your hydrangeas has aesthetic benefits, too. "Removing faded flowers creates a neat and tidy appearance, which many gardeners prefer over the look of leaving dried flowers on the plant," says Meyers.
Some gardeners report success in turning their hydrangeas blue by applying coffee grounds to the soil. The coffee grounds make the soil more acidic, allowing the hydrangea to more easily absorb aluminum. In addition, fruit peels, lawn clippings, peat moss and pine needles, are thought to have a similar effect.
Hydrangea Heat Stress
Heat and drought stress can cause the stomata of your hydrangea plant to remain open as they try to absorb water vapor from the environment that they are in. Unfortunately, this causes water to be lost more than it is gained which over time translates into wilting.
Symptoms of overwatered hydrangeas may include brown and wilted leaves, yellow leaves that will drop from the plant, and stunted growth. Signs of root rot may present themselves as well. This could appear that half of your plant is dead, and you may see white fungus near the crown of the hydrangea.
Shallow or inconsistent watering.
If a hydrangea is being watered every other day for twenty or thirty minutes (sadly, standard automatic irrigation settings) the plant is likely to wilt in hot weather. Once the flowers wilt a few times they will turn brown.
Soak your hydrangeas in water to rehydrate the stems and petals. First, cut each stem at an angle if you haven't already, then fill your sink with lukewarm water. Gently place your flowers in the water and let them soak for 15 minutes to 1 hour. You will see them perk back up to their lush fullness!
You should prune all unhealthy stems, leaves, and blooms back to the portion of the plant that looks healthy. Look for new growth or leaves and trim back to just before those areas.
If your hydrangea foliage is also damaged, it may be sunburned (crispy or brown around edges). Depending on the amount of total damage, your plant will eventually recover from severe sunburn, but may not rebound from extreme drought.
To reduce the size of a hydrangea that blooms on new wood, cut off about one-third of each stem in late fall or early spring before it begins to leaf out. If your hydrangea blooms on old wood, prune right after it has bloomed when the flowers are fading.
You can use multiple stems or use one stem for several cuttings. Cut the stem into 4- to 6-inch lengths with your knife or pruners. Cut each piece right above the node where leaves attach to the stem. These nodes are where new roots will form.