Hydrangea Pruning 101

How and when to cut back hydrangeas for vigorous growth and beautiful blooms.

By: Mark Wolfe

 

Given a favorable growing environment, hydrangeas are some of the easiest flowering shrubs to grow. They reward the grower with beautiful foliage and a gorgeous display of massive flower heads, or at least they are supposed to. Unfortunately these beauties cause perennial confusion when it comes to pruning. If your hydrangeas aren’t blooming, or the stems flop over under the weight of giant flowers, or the plants are filled with dead stems and you don’t know what to do, keep reading.

Before discussing how to prune hydrangeas, it’s important to consider whether or not they should be pruned in the first place. Most hydrangeas can live long lives and produce beautiful blooms year after year without ever being pruned. In some varieties, pruning can actually eliminate the flowers that you want. Pruning is not necessary to stimulate blooming, and should not be used as the long term solution for a plant that has outgrown its allotted space. However, judicious pruning can give your hydrangea a more lush, tidy appearance while stimulating larger flower clusters and a stronger branch structure.

How To Prune Hydrangeas

The critical bit of information that should guide hydrangea pruning is the timing of flower bud formation. Some hydrangea flower buds develop inside the stems over the course of a whole growing season, and then the flowers appear the following spring. This is “old wood” blooming. Other hydrangeas form flower buds inside the new growth that develops in spring and early summer, and their flowers bloom later in the summer. These are “new wood” blooms.

Prune hydrangeas that bloom on old wood in summer.

To avoid cutting off the next year’s flowers, old wood bloomers may be pruned, if needed, as soon as possible after bloom time. Avoid pruning these plants after the end of July. If the spent flowers are left to mature and dry on the plant, they may be removed at any time.

  1. Remove old blooms by cutting at the base of the cluster.
  2. Remove dead, old, or weak stems by cutting at the base of the stem.
  3. Lightly tip-prune for shape.
  4. If an older hydrangea appears a bit tired and weak, revitalize it by pruning up to one-third of the oldest stems down to the ground.

Prune hydrangeas that bloom on new wood in winter.

New wood bloomers may be pruned, if needed, any time after they drop their leaves in fall, but before they leaf out in spring. Some gardeners like to leave the dry flowers on the plant for winter interest. Pruning later may delay blooming until the end of summer, and may reduce overall flower production.

  1. Remove old blooms by cutting at the base of the cluster.
  2. Cut stems all the way back to promote larger flowers.
  3. For stronger stems, cut back by up to 25 percent of the height.

New Wood vs. Old Wood Hydrangeas

To know whether your hydrangea blooms on new wood or old wood, and how to prune it, you need to know its species. The hundreds of hydrangea cultivars available through lawn and garden retailers all come from just a handful of unique species.

Hydrangea arborescens, Smooth Hydrangea

  • Blooms on new wood
  • Allow two or three seasons to become established prior to hard pruning
  • Leave unpruned, or prune to the ground each winter
  • Popular cultivars: ‘Annabelle’, ‘Incrediball’, ‘Invincibelle Spirit II’, ‘Flying Saucer’

Hydrangea macrophylla, Big Leaf Hydrangea

  • Blooms on old wood
  • The most popular hydrangea produces large, globe-like (mophead) or flat (lacecap), blue, pink, or white flower clusters. Soil acidity affects bloom color.
  • Popular cultivars: ‘Nikko Blue’, ‘Penny Mac’, ‘Big Daddy’, ‘Charm’,‘Eldorado’
  • Some cultivars, like ‘Endless Summer’, bloom on both old and new wood. Treat them as you would other bigleaf hydrangeas.

Hydrangea petiolaris, Climbing Hydrangea

  • Blooms on old wood
  • This rugged vine rarely needs pruning, other than cutting out dead wood that may develop.

Hydrangea paniculata, Panicle Hydrangea

  • Blooms on new wood
  • Produces naturally strong branch structure.
  • Large cultivars are suitable for pruning to tree-form.
  • Popular cultivars: ‘Limelight’, ‘Vanilla Strawberry’, ‘Candelabra’, ‘Bobo’

Hydrangea quercifolia, Oakleaf

  • Blooms on old wood
  • Large cultivars may become unwieldy without occasional pruning to remove suckers and to eliminate the oldest stems.
  • Popular cultivars: ‘Alice’, ‘Pee Wee’, ‘Gatsby Pink’, ‘Ruby Slippers’

What Happens If You Don’t Prune Hydrangeas?

If left unpruned, otherwise healthy hydrangeas will continue to grow and bloom. They may even be better off without pruning, because the added foliage feeds the plant, enabling it to store up more energy. But removing dead stems and faded blooms improves their appearance, so a little bit of light pruning is beneficial in that regard.

If You Have Pruned Properly, Why Won’t Your Hydrangea Bloom?

For established plants that refuse to bloom, pruning may or may not be the problem. There are several reasons why a hydrangea may not bloom as expected, such as

  • Pruning at the wrong time
  • Stem dieback due to extreme winter cold or late spring freeze
  • Excess nitrogen in the soil, often due to runoff from adjacent lawn fertilization
  • Soil phosphorus deficiency
  • Inadequate sunlight

To get your plants back on track, do not prune them. Test the soil and fertilize based on soil test results. If trees have spread their branches overhead to block out too much sunshine, prune them lightly instead.

 

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Hydrangea Pruning 101
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Hydrangea Pruning 101
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Given a favorable growing environment, hydrangeas are some of the easiest flowering shrubs to grow. Unfortunately these beauties cause perennial confusion when it comes to pruning. If your hydrangeas aren’t blooming, or the stems flop over under the weight of giant flowers, or the plants are filled with dead stems and you don’t know what to do, keep reading.
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