The care information provided in this section represents the kind of practical advice is available for all the plants in this web site if you subscribe to the monthly customized newsletter Yardener’s Advisor.
Fertilizing - Keep It Light
Hydrangeas are fairly light feeders. Too much nitrogen deters bud production and increases the shrub's susceptibility to winterkill. Sprinkle a handful of an all-purpose granular fertilizer (preferably with a slow release form of nitrogen) on the soil under the shrub in the early spring. Do not feed them in the summer, because the new growth that will result is vulnerable to early fall frosts. Spread the fertilizer on the soil out to 1 foot beyond the tips of the branches (the drip-line). For more information about fertilizers see the file About Fertilizers
Mulching and Weed Control
Spread a layer of organic mulch 2 or 3 inches thick on the soil under each hydrangea. Either alone or over landscape fabric laid on the soil first, a mulch of chopped leaves, wood chips, pine needles, peat moss or the like, will deter serious weed problems and keep the soil moist longer. It will also protect shrub roots in the winter from heaving of the soil caused by its alternate freezing and thawing. For more information see the file on Using Mulch
Hydrangeas like moist soil. Not only is it important to water newly planted shrubs regularly for a few weeks, but even established hydrangeas appreciate supplemental watering if rainfall is irregular. In the event of a mid-summer drought it is particularly important to water as soon as the soil dries out.
Keeping the soil moderately moist is key. Hydrangea guru Michael Dirr author of Hydrangeas for American Gardens (Timber Press $29.95) recommends providing two inches of water weekly divided into two waterings, depending on the weather.
These shrubs will signal their thirst by drooping visibly the minute they feel dry. They wilt when the temperatures heat up. They lose moisture through transpiration faster than their roots
can take it up. So it's possible to water them well one day and find the plants wilting in the noonday sun the next. However, if the plant remains wilted in the morning, it should be watered immediately.
For more information see the file About Watering Equipment
Pruning and Grooming
Do not prune bigleaf hydrangeas by cutting back their shoots anytime except immediately after they bloom, lest you remove the wood on which the new blooms will appear. Flowers of bigleaf hydrangeas bloom on buds formed on the previous year's growth. Shoots severely pruned in the fall will take 3 or 4 years to recover and begin blooming. Instead, routinely thin out about 1/3 of the weakest, old growth of mature hydrangea shrubs each spring. Cut these old, weak canes back to the ground. For more information see the files on Pruning Shrubs and Choosing Pruning Tools
In zone 5, winter protection is the best way to ensure the mop heads bloom from year to year. When inverted over the shrub, a large gray plastic garbage can with its bottom removed makes a great winter cubbie. If the plant is too wide, gather up the stems and tie them together with old nylons or clothesline. When in place fill the can with autumn leaves. Tomato cages wrapped in burlap and stuffed with leaves will also work.
When spring arrives the covers are removed but the watch in not over. Cold winds and freezing temperatures of a late frost will quickly desiccate and kill the tender flower buds.
The past couple of winters we have suffered hard frosts in May that zapped the flower buds of many plants that had a history of successful bloom.
When frost threatens covering the plants with an old sheet, a floating row cover or a cardboard box will usually provide enough protection to keep the buds from dying.
Spraying the flower buds with an antidessicant such as Wilt Pruf may also afford a bit of protection over the winter, but in early spring it must be re-applied often to protect new growth. And be warned when temperatures (drop)below 5 or 10 degrees it loses it’s effectiveness so just using it for winter protection may not to the job.
If a late freeze zaps the flower buds on the tips of the branches on your mop heads, but the stems remain healthy, removing that dead terminal bud at the tip of the stem may activate flower buds further down the branch to flower. This should be done in spring when the plant begins to leaf out. You can tell if buds are dead because they will fail to turn green and grow.