When Should You Prune Hydrangeas?

Standard

20151108AThere’s a lot of confusion about when to prune hydrangeas. You hear all sorts of advice: spring, fall, after they bloom, not at all, etc. And in fact, when you prune varies, depending especially on the species you’re growing. Here is a summary:

  1. Hydrangeas that Bloom on New Wood

These hydrangeas bloom on new growth that is produced in the spring. Therefore they can be pruned in late fall, after they finish blooming, or in early spring. However, since their dried flowers remain attractive all winter, it makes sense to prune them in early spring, just after snowmelt, rather than in the fall. After all, why prune off several month’s worth of beauty?

Note that pruning is never obligatory for these species. If you never prune them at all, or simply limit your pruning to deadheading (removing the faded flowers), they’ll still bloom well. And even if you don’t deadhead, note that the faded flowers will fall off all on their own when the plant begins to grow in the spring.

Three species are commonly grown:

PeeGee hydrangea (Hydrangea paniculata) Zone 3

20151108B

PeeGee hydrangea

This hydrangea produces elongated clusters (panicles) of white flowers that turn increasingly pinker as fall advances. It’s is a very large shrub: most cultivars can reach 15 feet (5 m) in height and diameter if you allow them to grow entirely on their own.

With this shrub, pruning reduces the number of blooms, but gives larger flower clusters. If you want lots of flowers, prune little or not at all. If you want to keep the shrub more compact, prune back severely in early spring. If you prune it down to 6 inches/15 cm from the ground, by late summer you’ll get a compact plant about 3 to 4 feet (about 1 m) with extra-large panicles, although only a few of them. However, the wood won’t yet be fully developed and the stems can break under the weight of the blooms. A good compromise is cut it back annually back to about 3 feet (1 m) (still in early spring). This will give you a shrub about 5 to 6 feet (1.5-2 m) high with a decent amount of intermediate size panicles on stronger branches.

Smooth Hydrangea (H. arborescens) Zone 3

20151108C

‘Annabelle’ smooth hydrangea

This shrub is easily recognized by its globes or domes of white flowers (there are now a few pink-blooming cultivars as well) which bloom at the tip of the stems starting in the middle of summer. ‘Annabelle’, with its very round balls of white flowers, is the best-known variety.

For very even bloom, giving branches all the same length, cut the plant down to 4 to 6 inches (10-15 cm) in early spring or late fall. However, this gives very large flower heads that tend to flop. If this happens under your conditions, a lighter pruning many help, removing only the top 6 inches (15 cm) of the plant. The resulting stems will be thicker and the flower clusters smaller, giving a stronger plant not so prone to flopping.

Climbing Hydrangea (H. anomala petiolaris), zone 4

This hydrangea is not like the others and rarely needs pruning. Remove only winter-damaged branches and any that wander where you don’t want.

  1. Hydrangeas that Bloom on Old Wood

These hydrangeas bloom from branches produced the previous year, although some cultivars bloom also bloom to a certain degree on new wood, giving a second flush of bloom. In colder climates, these hydrangeas require very careful pruning, mainly consisting of removing dead wood in the spring, at snowmelt. Even deadheading can harm the delicate flower buds that form just below the old flower head, so if you do prune after the flowers fade, make sure to prune just above a pair of healthy buds.

Bigleaf Hydrangea (H. macrophylla), zone 6b

20151108E

Bigleaf hydrangea

Also called French hydrangea, mophead hydrangea (those with rounded flower clusters) or lacecap hydrangea (those with dome-shaped flower clusters), this hydrangea is renowned for flowers that can be blue in acid soils and pink in alkaline ones. I can be hard to grow in colder areas (north of zone 6) because of its limited hardiness. It’s best to try it in partial shade in rich, deep soil and in a sheltered spot protected from winter winds. In locations where snow cover is abundant and reliable, it may bloom well in zone 4 all on its own, but otherwise, it’s best to consider winter protection.

20151108F

Winter protection for tender hydrangeas

This hydrangea suffers not only from winter cold, but also spring frosts. Even when it breezes through winter with no damage, it tends to sprout almost immediately in spring, leaving the growing flower buds subject to late frosts. To ensure bloom on this somewhat persnickety plant, winter protection is advised anywhere late spring frosts are possible. In the fall, after the leaves have fallen, surround the plant with a “cage” of chicken wire 1 to 2 feet (30-60 cm) high and fill it with dead leaves. Leave this leaf mulch in place until there is no longer any risk of frost: until late May or even early June in most colder climates. The mulch will keep the soil cold longer, delaying sprouting… and thus protecting the future flowers.

Only after you remove the mulch and the plant begins to grow should you consider pruning… and even then, remove only dead wood!

Mountain hydrangea (H. serrata), zone 5

20151108G

Mountain hydrangea

This hydrangea is a near twin of the bigleaf hydrangea (H. macrophylla), but with thinner stems and smaller leaves. A little hardier than its cousin, it is theoretically winter-hardy to zone 5. Even so, its tender flower buds remain susceptible to damage from late frosts. In many climates, it is therefore wiser to give the cage-filled-with-fall-leaves treatment described above to ensure abundant bloom.

Oakleaf Hydrangea (H. quercifolia), zone 5

20151108H

Oakleaf hydrangea

This hydrangea needs little pruning, except to remove any dead or damaged branches, including those damaged by winter cold. If you do need to perform heavy pruning, perhaps on an older specimen that has outgrown its allotted space over time, the best time to do so is in summer, immediately after flowering.

Hydrangea Pruning for the Laidback Gardener

A lot of the information above smacks of hard work, so you might wonder what I do myself, as a laidback gardener, when it comes to pruning hydrangeas. The answer is simple: I don’t prune them at all. And I don’t offer winter protection, either, because I only grown varieties adapted to my conditions. I just let them grow, that’s all. Life is so much easier that way!

Advertisements

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s