Do I have to prune my hydrangeas?

First, let’s clear up that you do not HAVE to prune your hydrangeas. If you’re okay with them getting bigger, and like the shape they typically take, you can simply tidy them up by removing any dead branches and deadheading old flowers. 

If you have a defined space, such as under a window, beside a path, or your hydrangea is tree form (also called standard), you might want to give it a prune to keep it within the right size and shape for its location. If you find your hydrangeas branches are already very long and they tend to sag or bend in season under the weight of the flower heads or because of high wind or rain, this is a good reason to consider pruning the branches to encourage stronger, shorter branches. 

Many gardeners advocate waiting a few years to allow your hydrangea to become established before starting to prune it. Waiting before pruning allows your hydrangea to grow to its full size and potential before you start cutting it back.

There are 5 main types of hydrangeas, with new varieties being developed and released all the time. However, when it comes to pruning, most hydrangeas will fall into one of these three categories – they bloom on old wood, new wood or both. 

What does blooming on old wood or new wood mean? 

If the hydrangea blooms on old wood, that means that it will set its flower buds in late summer, not in the spring, so the flowers that you see were actually started last year. If you trim this type of hydrangea in the spring, you would likely be trimming off all of the flowers. 

If the hydrangea blooms on new wood, it means that flower buds will be produced on branches/stems that are grown that same year, so you can trim anytime after the plant blooms up until spring the following year. 

Blooming on both new and old wood means just that. It will grow new branches and flower, along with setting flower buds for next year all at the same time. 

Identifying Hydrangeas 

If you know what type of hydrangea you have, that certainly makes it easier to know when to prune! If not, here are some tips: 

  • Old wood hydrangeas will usually bloom earlier in the season, since they put that flower bud making work in the previous year. 
  • Panicle hydrangeas are more cone shaped than round, and these fall into the ‘bloom on new wood’ category. 
Summer garden with Limelight hydrangeas in the background, purple petunias and white alyssium in the foreground.
Photo Credit: Proven Winners

Which hydrangeas bloom on old wood? 

  • Bigleaf Hydrangeas (Hydrangea macrophylla)
    • Mophead Hydrangea. Perhaps the most popular Bigleaf variety. Loved for its large, round flower clusters, often in bold blue, purple, or pink. 
    • Lacecap Hydrangea. Produces clusters of delicate buds ringed by larger, flatter blossoms.
    • Mountain Hydrangea. An excellent choice for harsher climates. Its flowers resemble Lacecaps, with even smaller outer blossoms.
    • Reblooming Hydrangea. You’ll find this in both old wood and new wood lists because it blooms on both! Includes the Endless Summer variety. 
  • Oakleaf Hydrangeas (Hydrangea quercifolia). Named for its distinctive tree-like leaves, which change colors in the fall. This variety accents its leaves with clusters of delicate white flowers.
  • Climbing Hydrangea (Hydrangea petiolaris). The vertical-height champ of the family. This variety loses its leaves in the fall, revealing a distinctive peeling bark.

Which hydrangeas bloom on new wood? 

  • Panicle Hydrangeas (Hydrangea paniculata). Produce rich cone-shaped flowerheads. They’re often quite cold-tolerant. Includes the Limelight and Fire Light variety.
  • Smooth Hydrangeas (Hydrangea arborescens). which tend to remain fairly compact despite being a new-growth variety. Includes the well-known Anabelle and Incrediball, 
  • Reblooming Hydrangea (Hydrangea macrophylla). You’ll find this in both old wood and new wood lists because it blooms on both! Includes the Endless Summer variety. 

How to prune hydrangeas that bloom on old wood

Old wood hydrangeas typically require less work in terms of pruning, but if you do have to reduce their size, tidy up their shape here are our top tips: 

  1. As soon as flowering is over (typically no later than July), you can cut flowering stems back to a pair of healthy looking buds.
  2. Late winter or early spring is your chance to see the structure of the shrub and prune out weak or damaged stems. Remember to remove no more than 1/3 of the oldest stalks, taking them down to ground level.
  3. You can continue to do this every summer to help rejuvenate your hydrangeas and control their shape.

How to prune hydrangeas that bloom on new wood 

As noted above, these shrubs set their blooms on new growth, so they can be pruned almost any time of year, except summer. Here is how to approach pruning:

  1. Starting in late summer, you can deadhead spent flowers (or leave them up as winter interest), and trim any dead or crossing branches. 
  2. Anytime between late winter and spring, cut back the entire shrub based on your ideal size and shape. These hydrangeas are very forgiving, so don’t be shy and experiment with your pruning to find what works best for you and your gardens.

    1. Cutting shrubs all the way down to within 3” of the ground can produce larger blooms, but may create weaker stems.
    2. Cutting shrubs down to 18” – 24” can provide a bit of a framework to help support the new growth. 

Final Summary

Hydrangeas are lovely shrubs that come in a variety of shapes, sizes and colours that make a lovely addition to any garden. Hopefully this article has helped to make the thought of giving your hydrangeas a little haircut, a little less intimidating. So grab those pruners (if it’s the right time of year) and get out there!