Regional Gardening Reports :: National Gardening Association

In the Garden:
September, 2005
Regional Report

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Hydrangeas can be fussy to grow, and some even show a bad attitude!

Bloomin' Hydrangeas!

The big leaf hydrangea (Hydrangea macrophylla) we all know and love for its big, puffy, blue or pink mophead blooms, has to be the most perplexing, consternating, and confusing plant on earth. All hyperbole aside, too many gardeners have hydrangea trouble. The main complaint in our region is: "It doesn't bloom!"

Well, there are many possible reasons for this. One is too little sunlight. These shrubs need morning sun to bloom or very bright dappled light all day. Avoid hot afternoon sun unless you are in an area where summers are cool.

Another reason is too little water. Hydrangeas need an evenly moist yet well-drained soil. This means slightly damp like a wrung-out sponge, never sopping wet and never dried out. They will not do well in quick-drying pure sand or in waterlogged heavy clay, or in any soil that is bone dry. Water your hydrangea during dry spells, especially in the heat of summer, so it stays perky and fresh. Your hydrangea should never, ever be wilted in the morning.

Hydrangeas grow massive each season, so besides water they need rich soil. Ideally you should run some soil tests and fertilize based on the test results. But an annual topdressing of old, rotted manure or good quality compost along with a year-round organic mulch helps to feed the soil. You also may need to apply a slow-release, all-purpose granular fertilizer, such as 10-10-10, in early spring and again in early summer.

Pruning Cautions
Don't prune if you can help it. People tend to want to cut these back in the fall, but please don't! Most varieties bloom only on old wood -- the branches that grew the previous season. So do not prune in the fall or winter or spring. The only safe time to prune is immediately after blooming. Pruning should be limited to selective thinning if the plant has become overly dense. If you constantly need to prune for size, plant a smaller variety.

If winter damage forces you to trim back your plant in the spring, this will limit or eliminate blooming for the coming summer. Be very cautious about spring pruning for this reason. Wait until you are absolutely certain the branch is truly dead before you cut it off.

Cold Sensitivity
The biggest cause of poor blooming is cold damage. Most of these hydrangeas will do fine in zone 7; hardier cultivars may handle a typical zone 6 winter, especially if sited in a sheltered microclimate, but they only rarely bloom after a typically cold winter in zone 5. It is a sad fact, but those that suffer extensive winter damage and dieback will not bloom. Instead, you have a lovely, large, and leafy but flower-free plant. This would be a plant that is root hardy rather than bud hardy in your zone.

A frost after the buds have begun to swell or the plant has begun to grow also can reduce flowering. Such frosts happen often in spring when temperatures oscillate. The message here is to cover your plant if a frost is predicted, or if there is no cloud cover and you feel a frost in your bones. With hydrangeas, you're better off safe than sorry.

There are a couple of exceptions to the "blooms on old wood" rule, and I want to mention them because I have had so many questions about them recently. "All Summer Beauty" and "Endless Summer" are cultivars noted for their ability to bloom on both old and new growth. Under ideal conditions, these bloom over an extended period, first at the normal bloom time on the old wood, and then on the new growth of the current season. In practical terms, this means even if they are damaged during winter, they should still be able to bloom -- although later in the season -- on the new growth.

When killed back to the ground or close to it, when severely stressed by a hard winter, or when otherwise stressed by their growing conditions, mophead hydrangeas will definitely need optimum care to recover, grow lustily, and perform well. So please, whether you are growing one of the new high-performance varieties, or an old favorite, try to be realistic in your expectations.

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