The best place to overwinter your potted hydrangeas is in an unheated greenhouse, cellar, or garage. These rooms don't get direct sunlight and are kept at a moderate temperature (40 degrees Fahrenheit).
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. In colder climates, wrap or completely cover marginally hardy hydrangeas.
After the floral bud is developed, an additional 6 weeks at 2-9°C (35-48°F) is required for subsequent development of the flower. Hydrangea - Pg 2 3/1991 Page 3 3. T Plants are often forced at 16-17°C (60-62°F) night temperature.
The simplest method is to mound shredded leaves or bark mulch around the base of the plant to about 12 inches or so. Put the mulch mound in place in late fall after the ground freezes, and uncover plants in spring when temperatures begin to stay above freezing.
Hydrangeas are hardy, but if left in a pot over winter, it will be much colder than if left in the ground. The roots are much more vulnerable to freeze-thaw cycles if the hydrangea is planted in a pot. Pots can be brought inside during the winter, and then brought back outside in the spring and summer.
The best hydrangea winter protection for potted plants is to bring them inside prior to the first frost. If they are too cumbersome to move, they can remain outside and be protected by covering the entire pot and plant. One method is to use foam insulation to protect your potted plants.
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.
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.
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.
Most common hydrangeas prefer a partial sun location - ideally receiving sun in the morning hours and shade in the afternoon.
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.
Luckily, hydrangeas can tolerate some cold and are frost resistant due to their origins in Asia. But beware of severe (night) frost. Hydrangeas can survive the frost, but the buds can be damaged. And that would be a shame.
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.
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.
But when to prune them? Prune fall blooming hydrangeas, or old wood bloomers, after they bloom in the summer. If you prune old wooded hydrangeas in fall, you are cutting off next seasons blooms. Summer blooming hydrangeas, or those that bloom on new wood, are pruned in the fall, after they stop blooming.
While some plants bloom on new growth, others primarily set flower buds on old wood. Regardless, it is best to wait to prune all hydrangeas until spring. In the fall, hydrangeas (and all trees and shrubs) are in the process of going dormant. They do not produce very much new growth until the following spring.
Here are the four most common types of hydrangea: Panicle hydrangeas, sometimes referred to as Pee Gee Hydrangeas or Hydrangea paniculata, are a variety that blooms on new wood only. This group can be pruned in fall or very early spring, but we highly recommend waiting until the spring to reduce risk of injury.
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.
The size of your container matters, since the plant's roots will need room to grow into during their stay. We've found that pots measuring at least 16-24” wide and deep will often accommodate a good-sized hydrangea nicely for a few years.
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.