The last tell-tale sign of a Hydrangea with too much sun is the edges or tips of the leaves looking burnt. Burned edges and tips of leaves is called “leaf scorch” and occurs when there is too much sun on a plant that prefers more shade.
In warmer areas, many hydrangea types will suffer in the afternoon's scorching sun. The leaves and flower heads may burn, turning brown. If you notice this, that means your hydrangea is getting too much sun. Try moving it into filtered shade, or an area where it gets only a few hours of morning sun.
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.
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.
Typical symptoms include yellowing leaves, or irregular dry, brown blotches. Leaf tips and margins may turn brown, as well. Severely damaged leaves may drop from the plant. Leaf scorch results when the leaves lose water faster than it can be supplied by the roots, so wilting may occur before scorch is noticed.
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.
Removing a few crispy leaves or burnt mopheads is fine to improve your plant's appearance. However, resist the urge to prune severely and remove a large amount of the plant's foliage since that will cause further stress and a flush of tender new growth.
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.
"Soil that is either too acidic or too alkaline can quickly cause your hydrangea flowers to turn brown, so it's essential to have your soil tested to determine the right kind of fertilizer needed," she explains.
Many people think that you need a shady garden in order to grow hydrangeas. While that is true for some varieties, some hydrangeas thrive in sunny spots and even need full sun to develop into the fullest plants and the brightest blooms.
TOO MUCH SUN
Conversely, too much direct sun may stress hydrangea plants, which can force them to conserve energy by not forming flowers.
Bigleaf hydrangeas, also known as hydrangea macrophylla, vary especially with some of the newer cultivars being bred to better tolerate heat and sun, but most of these including the mopheads and lacecaps prefer some shade, especially during the afternoon.
Water at a rate of 1 inch per week throughout the growing season. Deeply water 3 times a week to encourage root growth. Bigleaf and smooth hydrangeas require more water, but all varieties benefit from consistent moisture.
But hydrangeas are among the few plants that can draw moisture in through their florets, so it's possible to perk up wilted blooms by completely submerging them in water and letting them sit for a few hours to rehydrate.
Panicle hydrangeas can handle hot sun
While they are drought tolerant and stand up to heat, I still like to provide shade during the hottest part of the day. And just because they are drought tolerant doesn't mean you should let them wilt. As with all hydrangeas, plants will thrive with regular irrigation.
Once leaf tissue is scorched, the damaged areas will not recover; however, minor damage, while unsightly, will not kill the plant. Leaves with scorched margins may look unappealing, but they still help the plant with photosynthesis, creating food for new, undamaged leaves to emerge.
Some plants died and others were fried by the record-breaking temperatures. Even some that look extremely bad, like rhododendrons and hydrangeas, can bounce back. Burned leaves don't necessarily equal a dead plant, so patience and observation is needed.
Yellow or Brown Leaves
When a hydrangea has been overwatered, one of the most obvious signs is yellow or brown mushy leaves. Touch your hydrangea's leaves just to make sure – dry leaves can be a sign of underwatering, so feeling them will help you tell the difference.
Water your hydrangeas in the morning before the heat of the sun is strong enough to quickly evaporate soil moisture. Try to avoid watering at night, which can encourage mold and mildew as the moisture sits through the cool night. Water your hydrangeas through the growing season as well as in late fall.
Mulch the plant to retain moisture. If the leaves are drooping, it is time to water the plant. If the leaves are yellowing and turning brown, check for standing water or a clogged drainage hole.