How to Prune Hydrangeas

Versatile hydrangea is a colorful flowering plant that can thrive in most USDA Plant Hardiness Zones, except in the coldest and hottest parts of the country. Its showy flowers bloom in round clusters that can fill up a plant and make for an impressive hedge or garden cluster. But it’s important to prune your hydrangeas. Unpruned, hydrangea can quickly turn into a mess.

We spoke with Denise Schreiber, an organic gardener and author, as well as garden designer Amy Fedele, whose website, Pretty Purple Door, helps home gardeners design beautiful, year-round landscapes. They shared their insights on why, when and how to prune hydrangeas.

Identifying Hydrangeas

The first step to pruning hydrangeas, Fedele says, is identifying which hydrangea you have. Some bloom on old wood (the previous season’s growth), some on new wood (the current season’s growth) and some on old and new wood. “If you don’t know what type of hydrangea you have,” she says, “you risk pruning incorrectly, resulting in an entire season with no blooms at all.”

According to Fedele, the most common types of hydrangea found in the U.S. are:

• Mophead/Lacecap hydrangeas (H. macrophylla, native to Japan), also known as French or Japanese hydrangea. Mopheads are the most popular type of hydrangea grown in home landscapes. They produce big ball-shaped flowers, usually in pink or blue depending on your soil acidity.
• Lacecap hydrangeas (Hydrangea macrophylla normalis) have a bit looser flower clusters but are treated exactly the same as mopheads.
• Panicle hydrangea (H. paniculata, native to China and Japan). Panicle hydrangeas are also known as peegee hydrangeas, hardy hydrangeas and Limelight hydrangeas, and have extended buds in a cone shape.
• Smooth hydrangeas (and H. arborescens, native to the eastern U.S.). Hydrangea arborescens are also known as snowball bush, wild hydrangea, sevenbark or sheep flower. They’re cold hardy. Annabelle (Hydrangea arborescens ‘Annabelle’) is a common variety of smooth hydrangea.
• Rough-leaf hydrangeas (H. aspera, native to southern and eastern Asia), including Sargent’s hydrangea (H. aspera subsp. sargentiana, native to China), have rough, oval-shaped leaves and broad, flat flower heads that sprout dispersed florets.
• Oakleaf hydrangeas (H. quercifolia, native to the southeastern U.S.) get their name from their large, dark-green leaves, which are shaped like those of a red oak. The flowers bloom white and turn to pink. Oakleaf are a popular choice because their leaves change color in the fall, to vibrant shades of orange and red.

How to Prune Hydrangeas

“If you don’t know what type of hydrangea you have, there is some pruning you can do for any type,” says Fedele. Otherwise, take a photo, or even a flower ball, from your hydrangea plant to your local garden center and ask for help identifying it. Pruning can be done with a clean, sharp pair of pruning shears sanitized with rubbing alcohol and dried.

Pruning for all hydrangeas

• Remove the spent flowers;
• Remove any branches that cross over each other;
• Remove branches that are damaged or weak.

“You can prune any [type of hydrangea] if there is a broken branch,”  Schreiber confirms.

Pruning mophead and lacecap hydrangeas

Both mophead and lacecap hydrangeas bloom on old wood, Fedele says. “Many find it easiest to prune after they are done flowering in the fall to prevent the risk of accidentally pruning off buds,” she says. “But you can also prune these in late winter/early spring while the shrub is still dormant.”

• Follow the dried flower down the stem down until you find two healthy buds;
• Snip about an inch or so above the buds.

“If you prune too early it will be hard to identify where the buds are,” Fedele says. “If you cut off the buds you will not have any flowers. It should come back the following year if you leave it be.”

Pruning panicle and smooth hydrangeas

Both panicle and smooth hydrangeas bloom on new wood, Fedele says. “They do not need to be pruned every year, but removing about one-third of the oldest branches each year will make for a fuller and healthier shrub and can stimulate more flowers,” she says.

Make sure you leave a set of buds on the stem below your cut. “The buds may be difficult to see when the shrub is dormant,” Fedele says.

Schreiber adds that, “Hydrangea paniculata (Panicle or PeeGee) and Hydrangea arborescens (Smooth or Annabelle) bloom on new wood so they can be pruned in late winter or early spring.”

Pruning rough-leaf and oakleaf hydrangeas

“Rough-leaf and oakleaf hydrangeas bloom on old wood and require very minimal pruning,” Fedele says. “Just trim any dead, crossing over or weak branches to maintain them.” Should they need any additional pruning, here are some guidelines:

• Because rough-leaf hydrangeas bloom on old wood, any pruning should be done immediately after it’s finished blooming.
• Overgrown plants can be cut back hard in mid-summer without affecting the next year’s blooms. “This is also the case for Sargent’s hydrangea, another popular rough-leaf variety,” Fedele says.
• If rough-leaf hydrangeas are pruned in the fall or winter, they will not produce blooms the following spring or summer. “If you’ve made this mistake,” Fedele says, “leave your shrub alone for an entire year and it should come back and flower in the next growing season.”

For oakleaf hydrangeas, Fedele says to prune the older growth when the shrub is finished flowering. This is usually in the fall or in early winter. Take less than one-third of the total growth to avoid cutting off next year’s blossoms.

About the Experts

• Amy Fedele is a garden designer; you can find her at Pretty Purple Door.
• Denise Schreiber is an organic gardener and the author of “Eat Your Roses, Pansies and Lavender and 49 Other Delicious Flowers” by St. Lynn’s Press. She’s also a national speaker, retired ISA Certified Arborist, All America Selections Trial Judge, a member of GardenComm, an Association of Garden Communicators, and Mrs. Know It All of The Organic Gardeners on KDKA radio.