How to Prune Hydrangea Plants

Hydrangeas are a favourite in many gardens, known for their showy blooms and lush foliage. Pruning these popular shrubs may seem daunting, but once you understand the specific requirements of each type, the process becomes straightforward. Proper pruning not only enhances flowering but also maintains the plant's shape and health. This guide will help you understand when and how to prune different hydrangea varieties, including tips on deadheading and dealing with common issues.

What is the Most Commonly Grown Hydrangea in the UK

In the UK, the most commonly grown hydrangea is the Hydrangea macrophylla, which includes both mophead and lacecap varieties. These types are particularly popular due to their large, colourful flower heads and relatively easy maintenance. Their adaptability to various soil types and the ability to thrive in both sun and partial shade make them a staple in British gardens.

When to Prune Hydrangeas

The timing of pruning depends on the hydrangea species. For those that bloom on old wood, such as mopheads and lacecaps, pruning should take place immediately after flowering, typically in late summer. This timing ensures that next year’s buds, which form soon after the flowers fade, are not accidentally removed. For varieties that bloom on new wood, such as paniculatas and arborescens, late winter or early spring is ideal, just before new growth starts.

How to Prune Hydrangeas

Pruning hydrangeas starts with understanding their growth habits. Begin by removing any dead or damaged stems back to healthy wood. Next, identify whether the plant blooms on old or new wood. This will guide how much of the plant you can safely cut back. The goal is to encourage strong new shoots, maintain a pleasing shape, and improve air circulation within the plant.

Deadheading

Deadheading involves removing spent flower heads to keep the plant tidy and to encourage more blooms. For mopheads and lacecaps, it’s best to snip off the dead flowers just above a pair of healthy buds. Avoid cutting too far down as this may remove potential flowering shoots. Deadheading is especially beneficial during the blooming season to extend the display of flowers.

Pruning Established Mopheads and Lacecaps

For mature mophead and lacecap hydrangeas, pruning is more about maintenance than shaping. Cut out one or two of the oldest stems at the base to encourage new growth and maintain an open structure. Avoid heavy pruning, as it may reduce flowering. If the plant has become overgrown or woody, a more significant rejuvenation prune can be carried out over several years to avoid shocking the plant.

Pruning Climbing Hydrangeas

Climbing hydrangeas, such as Hydrangea anomala subsp. petiolaris, require minimal pruning. Focus on removing dead or crossing stems and shaping the plant after flowering. This can be done in late summer or early autumn. Regular light pruning helps control its size and supports healthy growth, especially if it’s growing on a wall or fence.

Pruning Other Hydrangeas

Panicle and smooth hydrangeas benefit from more aggressive pruning, as they bloom on new wood. These varieties can be cut back to a framework of branches in late winter or early spring. This encourages large flower heads and a strong, compact form. It's important to avoid pruning too late into the growing season, as this may reduce flowering.

Problems You May Face and How to Combat Them

Several issues can arise when pruning hydrangeas. One common problem is cutting back too much, especially with varieties that flower on old wood. This can result in a season with no blooms. Another issue is failing to disinfect tools, which can spread diseases. Always use clean, sharp tools and make clean cuts. If hydrangeas look sparse or unhealthy after pruning, check soil conditions and water levels, as these can affect recovery. Late frosts can also damage emerging buds, so consider protecting plants if cold snaps are expected.