How to Prune Hydrangeas

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. Even if the buds become damaged over the winter, the plant can still flower on the wood it produces that season. 

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: 

• Feeling the wood on your hydrangea can help you tell the difference between old and new wood. Old wood should be stiffer, tougher, thicker and more brown, while new wood will be much more flexible, soft and should have a green tinge.
• “Old wood” means that buds are formed for next year’s bloom at the end of the current growing season, these hydrangeas tend to bloom earlier in the season and start to form buds for the next year in late summer.
• “New wood” means that the buds form on the current seasons growth after the plant leafs out in spring, and bloom a few months later in summer.

Which hydrangeas bloom on old wood? 

• Bigleaf Hydrangeas (Hydrangeas macrophylla) are the most common type of hydrangea, other common names include florist’s hydrangea, garden hydrangea and French hydrangea. There are two main types of bigleaf hydrangeas:
  • Mophead Hydrangeas are the most recognizable and popular varieties due to their large puffy flower heads.
  • Lacecap Hydrangeas look almost identical to mopheads, with the only difference being their flowers. They have tiny fertile flowers in the centre, with showy sterile flowers that surround the edge of the flower head.
• Mountain Hydrangeas (Hydrangea serrata) resemble bigleaf hydrangeas, but with better cold tolerance. Blooms are similar to lacecaps with flattened heads, but much smaller flowers and foliage.
• Oakleaf Hydrangeas (Hydrangea quercifolia) are named for its foliage which is shaped like oak tree leaves, as well the fact the leaves change colour during the fall (and are the only type of hydrangea to do so!). One of the few varieties native to North America, oakleaf hydrangeas can withstand a wider range of climate conditions than most bigleaf hydrangeas.

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.

Which hydrangeas bloom on new wood? 

• Panicle Hydrangeas (Hydrangea paniculata). Produce rich cone-shaped flowerheads. They’re often quite cold-tolerant. Includes the Fire Light, Limelight and Bobo series.
• Smooth Hydrangeas (Hydrangea arborescens). Have compact growth habit with abundant super-sized blooms on strong, upright stems. Includes the well-known Annabelle and Incrediball series. 
• 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 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.
3. Cutting shrubs all the way down to within 3” of the ground can produce larger blooms, but may create weaker stems.
4. Cutting shrubs down to 18” – 24” can provide a bit of a framework to help support the new growth. 

What About Reblooming Hydrangeas?

Also known as remontant hydrangeas, reblooming hydrangeas are types of bigleaf and mountain hydrangeas that have been grown to have the unique ability to flower on both old and new wood. Even if the buds become damaged in winter weather, the plant can still flower on wood it produces that season. Reblooming varieties include the Endless Summer series, Bloomin’ Easy reblooming series and certain varieties of Proven Winners Let’s Dance series.