Hydrangeas part 2: When to prune these colorful flowering plants

10/3/2017

The Japanese hydrangea vine is one of the 19th-century introductions from Japan that has remained a valued garden plant. It blooms in May.

THE WASHINGTON POST

Hydrangeas are my favorite flowering shrubs, and I know many of you will join me in the “I love hydrangea” fan club. I always love to have a big armful of their blooms on my table or tucked into arrangements around the house.

Having the bloom around the yard is heaven! So, when do you prune them? Good question!

Which kind do I have?

Last week, you figured out which kind of hydrangea you are growing. Here’s a quick recap:

Annabelle are usually the strong white snowball-like bloomers and grow on new wood. 

Bigleaf and mopheads (hydrangea macrophylla) are very common and have lots of different varieties with big leaves with jagged edges and huge poms of flower clusters in colors ranging from white to pink and blue. They set buds on stems that have bloomed. 

Lacecap flowers look different. Their flowers are spread out wider, and they look like a big lace doily. 

Oakleaf flowers look like a longer wand of flowers, and their leaves are shaped like a lobed oak leaf. Their foliage turns bright red in the late fall. The flowers grow on old growth in the late summer.

Peegees are a big group and are usually the ones with the bright pinks and bright blues. Some of these can also be shaped into a tree. Flowers start to grow on new growth in the spring.

When to prune

I’m just going to be bold here and give you some dates. But remember, you have to listen to Mother Nature a bit, too.

So, here’s my quick answer — there is nothing to prune right now unless it is damaged or diseased. Don’t prune any hydrangea between Aug. 1 and Feb. 1. Then, you will have two main windows of pruning time, depending on the type of hydrangea in your landscape: mid-summer and late-winter. But many of you want to put a date on a calendar, so I am going to give you a general window of time. Some can be pruned between Feb. 1 and March 30 and others before Aug. 1.

Why can’t it be simple? Look at it this way: If you plant a lot of different types of hydrangea, your shrubs can be blooming almost all year long.

Early summer pruning: bigleaf, lacecap, mophead, oakleaf hydrangea (H. quercifolia).

Hydrangea macrophylla is pruned in the summer. Pruning before Aug. 1 is a good rule of thumb. Always wait until the summer blooms have faded, then you can reshape them. If they are strong in control, then don’t prune them at all. They will thrive even without an annual pruning.

Most set their flower buds at the ends of the upright or lateral branches, during late summer to early fall. That is why it is key to prune before they have a chance to set their buds. If you wait to prune in the fall or early spring, you will cut off all of their hard work.

So here’s the tricky part: Bigleaf and oakleaf hydrangea both flower on previous year’s growth, so both should be pruned shortly after their blooms are done. Here’s the twist: Bigleaf hydrangea will be done flowering mid-summer, so prune before Aug. 1. Oakleaf are done in the late fall, so prune in the spring.

Oakleaf hydrangeas are typically pruned in early spring, as their colorful fall foliage is often a welcome sight in autumn. Oakleaf hydrangea blooms on new season growth and can be pruned in late winter or early spring, while dormant, to remove dead wood. If it has experienced winter dieback, prune back to below the point of injury.

Late winter to early spring pruning: Annabelle or smooth hydrangea (H. arborescens), peegee hydrangea (H. paniculata), tea of heaven (H. serrata).

Spring is the most common time to prune most of the hydrangea varieties. Annabelle (smooth), peegee (panicle), and tea of heaven flower on current year’s growth and can be pruned anytime from late winter until early spring. Try to prune before leaves appear.

Just to be safe, prune them late winter or trim dead growth in early spring just prior to blooming. Some people like to prune Annabelle to the ground in late winter.

Peegee varieties set new flower buds on new spring growth. Some can be trained to look like small trees. Pruning these will also encourage more new growth and hopefully more flower buds.

But you know how it goes; there are always rule breakers. And with hydrangea, we call them “anytime pruners.” “Endless summer” and “lime light” are repeat bloomers. You might get a few cycles of blooms even if they are pruned after they bloom. Hallelujah!

Where to prune

When you prune your hydrangea, keep their growth habits in mind. Make your pruning cuts with clean and sharp pruners, cutting just above the first set of large leaves. You can also look for the last healthy bud and cut just above it, making a sharp diagonal cut.

This will keep next year’s bloom intact. Leave the stem alone if you see buds. Take out any weak stems to the ground and cut, or deadhead spent flowers and stems to the last bud.

Don’t prune out all the old wood, since this is what will keep flowering as the new growth matures. Deadhead flowers off the tips as soon as they are dry, and reshape the plant if it is getting out of control, but never remove more than a third of the shrub a season.

This is the time to thin the shrub. Look for stems that are really old. They will be big, thick branches that look very woody. You can cut those a few inches from the ground. You can also get rid of the tiny stems that are smaller in diameter than a pencil. Next, get rid of any branches that cross each other.

Magical powers

Yes, these favorite blooming shrubs have magical powers. They can’t cure cancer or make you invisible, but they can make the flowers change colors. It is all in the soil. Acidic soil makes flowers turn blue; alkaline soil makes them turn pink.

OSU extension says, if you have pink flowers and you want to turn them blue, you need to do a soil test. Your soil might be low on aluminum, or your soil’s pH is too high.

Contact Kelly Heidbreder at: getgrowing@gmail.com