As spring approaches, do not get sucked into the hydrangea pruning black hole of fear. There are so many varieties of beautiful hydrangea, and worrying over what and when to prune can take way longer than doing the actual job itself.

So, let’s break it down!

Why do hydrangeas need pruning?

Pruning prevents hydrangeas becoming woody and congested, and channels the plant’s energy into producing strong growth and large, beautiful blooms.

When to prune?

As a general rule, most hydrangeas are pruned in late spring (climbing hydrangeas are the exception to this rule as they are pruned in summer, after flowering).

The faded flowerheads left on over winter offer frost protection to the buds beneath, until the worst frosts are over. Further south, pruning can be done in late winter but in Scotland, we can have frost and snow through early spring so wait until a bit later, around late March or early April, to prune. The occasional late frost is unlikely to do much damage, but a prolonged bout of freezing weather could damage newly exposed buds.

What to prune?

Hydrangea macrophylla, Hydrangea aspera, Hydrangea serrata, and Hydrangea quercifolia are lightly pruned by cutting back the old flower heads to a pair of buds below. Hydrangea paniculata and Hydrangea aborescens can be cut back harder.

Different types of hydrangea are pruned in different ways which is what causes all the pruning confusion: some flower on old wood, and some on new. Pruning incorrectly will affect flowering.

Old Wood

Plants that flower on old wood set their buds last year so if you chop them back too much in spring, you can cut off the buds which would have flowered meaning you would not have any flowers this year.

The most common group of hydrangeas seen in domestic gardens is Hydrangea macrophylla, which divides into mop-heads and lacecaps.

Pruning is normally minimal unless the centre of the shrub has become congested.

New Wood

Flowering on new wood means that the plant grows the stem with the flower on it within one year. If you prune them back in spring, they still have time to grow new wood with buds on it.

Hydrangea paniculata and Hydrangea aborescens produce flowers on new wood, which means that you can cut them back harder without losing this year’s flowers.

The flowers tend to be conical in shape, white to begin with, gradually turning pink or lime green.

Not Sure?

The easiest way to know what kind of hydrangea you have is to check the label when buying it, and keep hold of it.

If you already have a hydrangea of which you are unsure, the flower and leaf shape will tell you which is which, but it is best just to deadhead it and observe how it grows over the season to be sure, noticing if it flowers on this year’s growth.

How to prune?

You need a good pair of sharp secateurs.

Flowering on Old Wood

Remove spent flowerheads to just above a pair of new buds – hydrangea buds can be easily knocked off, so cut carefully using the tips of the secateurs.

Remove damaged, diseased, or crossing branches, and cut out any thin, weak stems around the base of the plant, removing one or two of the oldest stems from as low down as possible to promote new shoots from the base. These will grow over the next few years and carry blooms in the future.

If you have a really overgrown, straggly shrub, cut around a third of the stems right to the base.

Flowering on New Wood

Hydrangea paniculata and Hydrangea aborescens are more vigorous growers so last year’s growth can be pruned back to a healthy framework between 30-60cm high. Prune to just above a pair of healthy buds on each stem.

If you want bigger flowers, but less of them, cut back to the lowest healthy buds, or cut back less hard for a taller plant with more, smaller flowers.

Prune away any side shoots that are a bit spindly or weak.

What happens if hydrangeas are not cut back?

Well the sky does not fall in! If you do not prune hydrangeas then they can resemble a tangled mass of woody stems, and the flowers will become smaller and less showy after a few years.

Lack of proper pruning is the number one reason why hydrangeas do not flower.

If In Doubt, or Shaking with Fear

Although hydrangeas will look better with a proper prune, simply deadheading back to the first new set of buds works for both hydrangeas flowering on old wood and those flowering on new, as a temporary measure until you feel more confident.

Try to also take out any dead or diseased stems at the same time, or any stems that are crossing over or rubbing against other ones.

Once you have mastered the basic pruning method, try one step further next year, and start to think about the overall shape of the hydrangea. If you only ever deadhead down to the first set of new buds, then you will eventually end up with flowers round the edge and a tangled mess in the middle. In order to get a nice rounded shape, cut back harder at the bottom, or the front if planted against a wall or hedge, to the second or third pair of fat buds.