How to prune hydrangeas – the crucial difference between old wood bloomers and new wood bloomers

If you’re wondering how to prune hydrangeas, there isn’t a one-size-fits-all rule – at least, your hydrangea falls into one of two categories.

Some hydrangeas flower on old wood, while others flower on new wood, and each category tolerates a different level of pruning. It’s all down to the species – and whether you’re growing hydrangeas in pots or borders, it’s crucial that you identify the type before you start trimming.

Here's how to prune hydrangeas according to the species you’re growing.

What you'll need

• Some anvil secateurs for dead stems, like the Spear & Jackson Razorsharp Geared Anvil Secateurs, now £9.96 at Amazon
• A pair of bypass secateurs for cleaner cuts on green growth, like the Darlac Compact Plus Pruner, £11.95 at Amazon
• A tool cleaning product, like Agralan Citrox Ready To Use Natural Citrus Disinfectant Spray, £11.99 at Amazon

How to prune hydrangeas that bloom on old wood

Hydrangeas that flower on old wood include species like:

• Hydrangea macrophylla (mophead and lacecap hydrangeas)
• Hydrangea quercifolia (oakleaf hydrangea)
• Hydrangea serrata (mountain hydrangea)

These kinds of hydrangeas don’t strictly need pruning, but if you do give them a trim, it’s best to do it lightly. Here’s how…

1. Prune at the right time

Knowing when to prune hydrangeas is just as important as the how – and for varieties that bloom on old wood, it’s important that you’re not removing next year’s blooms.

‘My top golden rule is to prune immediately after flowering in summer,’ says Mark Dwelly, head gardener at Audley Stanbridge Earls. ‘This allows time for fresh shoots to develop and form buds for next year’s display.’

That means you’ll need to avoid pruning these types of hydrangea in the autumn or the spring, or else you could be cutting away next year's blooms.

2. Keep it light

Pruning hydrangeas that flower on old wood too hard can ruin their chance of flowering next year, so it’s best to tread carefully and stick to removing the three Ds: dead, damaged and diseased stems.

‘Once flowering has finished, deadhead the faded flowers and remove any weak or dead stems,’ says Elise Harlock, flower expert at Prestige Flowers. ‘This keeps the plant tidy without sacrificing next year’s flowers.’

Make sure you’re cleaning your garden tools properly between pruning sessions to avoid spreading diseases between plants.

‘It's also a good idea to consider thinning out a few of the oldest canes right down to the base,’ adds Mark. ‘A rule I often consider is to never take more than a third of the plant in one season.'

3. Consider leaving the flowerheads over winter

There are some plants you don’t need to deadhead, and hydrangeas are one of them. In fact, leaving the flowerheads on over winter can benefit wildlife and the plant itself.

‘Dried flower heads not only add sculptural winter beauty, but also act as a natural shield for developing buds against frost,’ Mark explains. ‘These can be trimmed back in early spring, cutting just above the first healthy bud.’

How to prune hydrangeas that flower on new wood

If you’re growing a hydrangea that blooms on new wood, you can use the secateurs a little more liberally. Species that fall under this category include:

• Hydrangea paniculata (panicled hydrangea)
• Hydrangea arborescens (smooth hydrangea – 'Annabelle’ is one of the most popular varieties)

1. Time it right

Hydrangeas that flower on new wood produce buds on new growth in the spring, so it’s best to prune right before the first shoots appear.

‘These set their buds on fresh growth each spring, so late winter or early spring is the ideal time to cut them back,’ says Elise.

2. Cut them back

These types of hydrangeas tolerate a much harder prune than those that bloom on old wood, which is why Mark says you should be bold when it comes to cutting them back.

‘Unlike old wood bloomers, these hydrangeas respond well to stronger pruning,’ he explains. ‘Cutting them back by one-third to one-half of their height encourages healthy new shoots and a well-shaped plant.’

Before you do that, though, you’ll need to remove any dead, damaged or diseased stems.

‘This can help to prevent future problems and keep plants strong and productive,’ Mark says.

So, now we know the key to pruning hydrangeas successfully: identify whether your plant blooms on old or new wood, and trim accordingly!