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.
Mulch Matters
Weird winters with little snowfall and drastic temperature swings are detrimental to plants. To give hydrangeas their best chance at success, apply a layer of chunky mulch around the base of the plant. Decorative mulch is helpful but we recommend straw, marsh hay, or fallen leaves.
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.
New Wood Bloomers
These are the hydrangeas that set flower buds on current season wood (new wood). It is easy to grow these hydrangeas because they bloom every year regardless of how they are cared for or treated. They can be pruned to the ground in the fall and they will emerge in the spring with bountiful blooms.
In late winter or early spring, these shrubs can be cut all the way back to the ground. Smooth hydrangeas will produce much larger blooms if pruned hard like this each year, but many gardeners opt for smaller blooms on sturdier stems.
Hydrangeas that bloom on new wood require pruning in late winter or early spring. Prune to shape, cutting back to about two feet. The pruning promotes new, sturdy growth, which provides the blooms next season. There are two varieties in our area that bloom on new wood.
To prepare hydrangeas for winter in colder areas, add a thick layer of mulch around the base of the plants to protect the crown and roots from freezing temperatures.
"If you want a longer stem, you can make a deeper cut as long as it is done before July or August when the plant begins forming buds for next year's flowers," she says. For smooth hydrangeas, remove the spent flowers as soon as they fade to green to ensure a second flush of smaller blooms in the fall.
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.
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.
Without going through the deadheading process, hydrangeas will not produce as many flowers and the few produced may not grow as big to their full potential.
Other times, you might need a fork or shovel to help divide the plant. Either way, once you have two pieces with roots attached to each, you now have two plants to replant. The best time to divide bigleaf hydrangeas is very early spring, just as new green buds are starting to swell and open along the stems.
You can use multiple stems or use one stem for several cuttings. Cut the stem into 4- to 6-inch lengths with your knife or pruners. Cut each piece right above the node where leaves attach to the stem. These nodes are where new roots will form.
If you prune them at the wrong time, you could risk cutting off all the flower buds and ending up with no blooms that year.
Cut back any clearly dead branches, which are brittle and snap off easily. This can be done in the fall or any time you see a dead branch. To reduce the size of a hydrangea that blooms on new wood, cut off about one-third of each stem in late fall or early spring before it begins to leaf out.
Regardless of the type of hydrangeas you're growing—and whether it blooms on old or new wood—the cutting process is the same. Start by using clean, sharp shears, then make your cut. "Cut stems above a node, and include at least two leaf groups on the cut stem," says Godshalk.
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.
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®.
New varieties, like Summer Crush, can produce on old and new wood. It's better leave as much old wood as possible through the winter and spring to ensure blooms.
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.