Pruning hydrangeas depends on species

For the HeraldMarch 7, 2013 

Every time you turn around, plant breeders are coming up with a a hydrangea.

In the old days, hydrangeas were beloved, but gardeners had a hard time figuring out how to prune them. That’s because species are pruned differently. Now with the new cultivated varieties, it’s even more confusing. Thankfully, Tim Wood at Proven Winners has made it much easier.

All you need to know is the size and color of the flowers to know which hydrangea is which, then you can figure out how to prune it. If your plant has big pink or blue flowers, it’s a big-leaf hydrangea (Hydrangea macrophylla). Hydrangeas with round white or pinkish flowers are smooth hydrangeas (Hydrangea arborescens). Hardy hydrangeas (Hydrangea paniculata) have white, greenish or pink conical flowers.

Big-leaf hydrangeas don’t need much pruning, Wood said. Prune a few of the oldest stems down to the ground each year, removing no more than one-third of the total stems in one year. Do this after they flower in the summer. Don’t prune these in late winter or spring. Big-leaf hydrangeas flower on older wood, so pruning before flowering removes the flower buds.

The smooth hydrangeas bloom on new wood or the wood that will develop in the coming season. These should be pruned back to a height of one to two feet in late winter. This helps encourage stronger stems that are less likely to droop over with the weight of big flower heads.

The hardy hydrangeas are pruned back to the ground or, if you want taller plants, prune back to within one to three feet from the ground. They also bloom on new wood.

Many of the new hydrangeas on the market originally come from Spring Meadow Nursery, which specializes in the propagation of “new and superior ornamental flowering shrubs” and introduces them to gardeners through the Proven Winners marketing program.

To make things more confusing, Spring Meadow Nursery has developed a line of “reblooming” large-leaf hydrangeas. Their line of Let’s Dance hydrangeas bloom on new and old wood. Right after flowering, deadhead spent flowers by cutting back to the first set of leaves beneath the flower head. After they bloom, prune out any dead, thin or weak wood down to the ground.

New to the Let’s Dance line this year is Let’s Dance Diva. Diva has a huge flower head made up of flowers with baby pink petals (actually sepals) as big as the size of your hand. Another new Spring Meadow rebloomer is Paraplu with large candy pink to hot pink mophead flowers. The individual flowers (called florets) are double, giving it a unique softer look. Paraplu supposedly holds up well in summer heat. It also has a compact habit, reaching only 21⁄2 to 3 feet tall and wide, making a neat little hydrangea shrub.

In my landscape, I have Incrediball, a Spring Meadow introduction. It’s a smooth hydrangea with gigantic white-flower heads that can reach 1 foot in diameter. One flower looks like an entire bouquet. The round flower heads are definitely incredible. The shrub grows to 48-60 inches tall and wide.

-- Marianne C. Ophardt is a horticulturist for Washington State University Benton County Extension.

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