The further north your garden is located, the more sunlight your hydrangeas need. An average rule of thumb is six hours of sunlight per day. However, hydrangeas growing in the south can perform on only three hours of sunlight.
Too Much Sun
"If you live in zone 4, you can get away with almost full sun," says Mcenaney. "But if you live in zone 7 to 9, you really want to restrict the sun exposure to a few hours in the early morning to avoid scorching the leaves and blooms."
Most hydrangeas prefer only morning sun. Yet one type of hydrangea can soak up the sun all day: the panicle hydrangea. While they can stand the sun, these do just fine in partial shade, too. Plus, panicle hydrangeas are the hardiest hydrangeas.
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.
Hydrangeas are hardy in growing zones 3-7 and will need at least 4-6 hours of sun a day. They can get by on 4-6 hours if they are located in partial shade. If you don't know which growing zone you are located, check out this interactive USDA hardiness zone map here.
TOO MUCH SUN
Conversely, too much direct sun may stress hydrangea plants, which can force them to conserve energy by not forming flowers.
Can hydrangeas grow in full sun? Hydrangeas like morning sun, but do not do well if they're in direct, hot afternoon sun. Partial shade in the later parts of the day is ideal for these beauties.
Provide Some Shade
Most varieties of hydrangea prefer shade during the heat of the day. Most varieties of hydrangea prefer afternoon shade. If you think your hydrangea can benefit from a break from the sun you can purchase shade cloth online or from your local garden center.
4. All hydrangeas will turn brown if they wilt too many times in hot weather. Water these shrubs deeply every few days in the heat of the summer (note that hand watering isn't deep enough) and mulch around plants to hold moisture in the soil longer.
The hydrangea should be watered thoroughly at least 3 times a week. Always water the plant all the way around the container, not just in one place. Water should come out the bottom of the pot. Never let it sit in water which will cause the roots to rot away.
It depends on what kind of hydrangea you have, but typically both Endless Summer® hydrangeas and panicle hydrangeas will bloom in afternoon sun. If it's only a couple of hours, then you may not get as many flowers as if they were planted in areas that get 4-6 hours of morning sun.
Hydrangeas can be grown in full sun but too much direct sunlight, especially during the afternoon hours when the sun is most intense, can cause wilt. When exposed to excessive sun, the plant's internal temperature increases, which causes the leaves to transpire and leads to moisture loss in the cells.
Hydrangeas grow best in full sun (more than 6 hours sun) to part sun (4-6 hours sun). With that being said, all hydrangeas can handle some shade, but the timing and type of shade are important to consider. They can be in full shade during the hottest part of the day, as long as they are getting some morning sun.
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.
While several species of hydrangeas thrive in shade, panicle hydrangeas (Hydrangea paniculata) are the best for growing in full sun. These summer-blooming shrubs produce large clusters of white flowers for several weeks.
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.
If you're growing hydrangeas, use coffee grounds to affect their color. Coffee grounds add extra acidity to the soil around hydrangeas. On a chemical level, this increased acidity makes it easier for the plant to absorb naturally occurring aluminum in the dirt. The effect is pretty blue clusters of flowers.
Apply mulch, preferably a reflective mulch such as dry grass clippings. The first line of defense against hot weather and the windy conditions that can dry surface soil is to apply a liberal layer of mulch around the plants. This protects the soil from direct sun exposure, keeping it moist at the surface.
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.
Hydrangeas need more water than most garden plants and will begin to wilt quickly without it. To ensure that Hydrangeas thrive, water deeply two to three times a week in the summer. Be sure to water in the morning or evening so that water does not evaporate as quickly as it would during the heat of the day.
Keep good air space between the plants; don't crowd them together or against other plants. Don't give bigleaf hydrangeas too much love; if they're too comfortable (water, fertilizer, etc.), they may devote all their foliage to leaves instead of blooms.
Hydrangeas do best in moist, well-drained soil and dappled shade – not too sunny and not too shady. Avoid south-facing positions, especially if the soil is very dry. For a very shaded spot, such as a north-facing wall, grow the climbing hydrangea Hydrangea anomala subsp.
The combination of too much sun and not enough water is a common cause of hydrangea droop, making it a great place to start when your plants are feeling unwell. Check the moisture level of your hydrangea at a point 1 to 2 inches (2.5-5 cm.) below the surface of the soil with your finger.