Frost and cold can harm a Hydrangea, but thankfully, these plants are relatively hardy. Though it may affect this year's blooms, if pruned appropriately, Hydrangeas damaged by frost will most likely return to their old selves with a little bit of TLC.
Paniculata and smooth hydrangeas do not need protection in the United States and most of Canada. Hydrangeas that experience winter temperatures of no less than 5-10 degrees do not need winter protection. If the temperature falls into the single digits for only a few hours at a time, the hydrangea should not be harmed.
The hardiness zones for H. macrophylla are 6 to 9. Effectively, a hydrangea should be able to sustain a temperature of minus-10 degrees. But in the real world, temperatures as low as 12 degrees — and late fall or early spring freezes — may reduce the flowering capability of this hydrangea.
Some varieties, like smooth hydrangea (“Annabelle”) and panicle, or PG hydrangea, are very cold-hardy and bloom on new wood. If these are the species in your garden, you don't have to worry about winter kill on hydrangea. They don't need protection unless the temperature dips below negative 30 degrees F.
They're supposed to lose their leaves this time of year. Make sure it stays hydrated throughout the winter if you don't have snow cover. Even though the plants are dormant, they still need some hydration at their roots. Snow cover not only provides insulation, but also a water source.
Whether or not hydrangeas need protection depends on how cold the winter temperatures drop. If the air temperature doesn't go below 0 degrees (zone 7) there is no need for winter protection.
4. No need to prune. If you trim your plants in fall or winter, you may mistakenly remove flower buds for the following year on bigleaf and oakleaf hydrangeas. Leaving the old flower heads on the plants will also add some interest to the winter landscape.
Most common hydrangeas prefer a partial sun location - ideally receiving sun in the morning hours and shade in the afternoon. The reblooming Endless Summer® Hydrangea series prefers part shade. These include BloomStruck®, Endless Summer®, Blushing Bride®, and Twist-n-Shout®.
As rapid growers—averaging about 2 feet of growth per year—larger varieties of hydrangeas can reach up to 15 feet tall. Applicable in growing zones 3 to 9, hydrangeas are a low maintenance plant that will return year after year with proper care.
Transplant Shock
The hydrangea drooping after planting or transplanting is common. Even if you carefully dig out the entire root ball, damaging some of the fine roots is inevitable. Also, the plant needs time to adapt to the new soil conditions.
Hydrangeas that bloom on new wood can be safely pruned in late fall once the plants have gone dormant or in early spring. Next year's flower buds won't be formed until late spring the same year they bloom, so there is no risk of removing the buds if you prune in fall or spring.
If you don't prune hydrangeas then they can eventually resemble a tangled mass of woody stems, and the flowers will become smaller and less showy.
Prune these hydrangeas only after bloom in the summer and not in the fall. Old wood hydrangeas start developing their bloom buds for next year in August and September. If you don't prune your hydrangeas real soon, then it is better to wait until next year. Otherwise you won't have any blooms next spring.
Watering Newly Planted Hydrangeas
You do not want to plant them in an area that has standing water, especially after rainfall. Hydrangeas in the ground should be watered at least 3 times a week when planted to help establish a strong root system. They have shallow roots so mulch is an absolute must!
"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.
Deadheading your hydrangeas isn't a care step you want to skip. "Deadheading allows the energy produced by the plant to go into the leaves, stems, and roots (rather than forming seeds) for future growth," says Melinda Myers, a professional gardener.
There are several different types of hydrangeas—bigleaf, panicle, smooth, oakleaf, mountain. All these types should be fertilized at least once a season in late winter or early spring, certainly by the time new growth begins to show around the base of the plant.
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 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.
The reason for a hydrangea dying is most often due to not enough moisture in the soil. Hydrangeas require the soil to be consistently moist and will droop or die because of drought. Hydrangeas can die due to frost damage, drought, transplant shock and because of too much sun.
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.