Generally, hardier hydrangeas such as the paniculata and arborescens types don't need extra winter protection. However, extreme cold can cause die-back of their branches. If a colder than normal winter in predicted, consider covering.
The primary reasons hydrangeas don't bloom are incorrect pruning, bud damage due to winter and/or early spring weather, location and too much fertilizer. Hydrangea varieties can be of the type that blooms on old wood, new wood or both. Old wood is the current year's growth and new wood is next year's (spring) growth.
Know when they're beyond repair.
If you catch and treat your hydrangeas when their blooms first start turning brown, Myers says there's a good chance you'll be able to turn them around (as long as it's not due to weather damage). "However, once they turn fully brown, there's not much you can do," she says.
Panicle Hydrangea
Blooms will begin appearing in July, continuing into the fall. The plants do best in full sun and well-drained soil and are hardy in Zones 3-8.
Remove the wilted hydrangeas from your arrangement and re-cut the stems on a 45-degree angle. Make a vertical slit in the incision and hold the stem upright in the boiling water for about 60 seconds. Place the hydrangeas back in your floral arrangement and they should revive themselves in an hour or so.
Frigid winter temperatures, as well as winter winds, can cause winter kill on hydrangeas. The low winter temperatures can kill the plant, or they might die because of drying out caused by winds.
The Bottom Line
If extreme cold weather has damaged your Hydrangeas, they will most likely recover. These plants are hardy, and though they may not rebloom this year, as long as you prune back the damage done, you should start to see its beautiful flowers the following 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.
Miracle-Gro Performance Organics Blooms Nutrition
This is an all-purpose blossom booster that's suitable for use on a wide variety of perennial and annual blooming plants, including hydrangeas.
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.
With their vibrant, plump blooms, hydrangeas offer a striking display in the warm weather - but what do they look like in the winter? As the delicate petals fade in the colder months, bright hydrangeas can quickly appear dry and brown - requiring targeted care to get them flowering again in April.
Indications for a Dying Hydrangea
Hydrangea leaves turn black or brown due to frost damage. Yellow and dry leaves due to too much direct sun. A drooping hydrangea results from low moisture levels from fast-draining soil and too much sun. Root rot due to poor drainage and bad watering habits.
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. Plants that are pruned at this time are at a greater risk of winter injury because new growth at the site of wounds is more susceptible to extreme cold.
The reason for hydrangeas wilting and dying is because there is not enough moisture around the roots due to lack of watering or rainfall, the soil drains too quickly, too much sun or excessive wind saps moisture from the leaves. Hydrangea flowers can droop due to excess fertilizer.
Important: Since hydrangeas tend to set their blooms on the ends of the branches, it is important to keep these covered all winter. Most insulating materials will pack down somewhat during the winter and expose the branch tips, so the material must either be replaced or secured in place.
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.