Knowing how to prune hydrangea macrophylla is the key to keeping these popular shrubs healthy and blooming beautifully. Many gardeners are nervous about cutting them back, but with the right timing and technique, it’s a simple task. This guide will walk you through the process step-by-step, so you can prune with confidence and enjoy a spectacular show of flowers.
Bigleaf hydrangeas, as they’re often called, are unique because they bloom on old wood. This means the flower buds for next summer are formed on the growth from the current year. If you prune at the wrong time or too aggressively, you’ll accidentally remove those buds and miss out on blooms. The good news is that these plants require minimal pruning to thrive.
How to Prune Hydrangea Macrophylla
Before you make a single cut, it’s crucial to understand the type of hydrangea you have. Hydrangea macrophylla includes two main groups: mopheads (with large, round flower clusters) and lacecaps (with flat clusters of tiny flowers surrounded by larger ones). The pruning principles are the same for both. Always start with clean, sharp bypass pruners to make smooth cuts and prevent disease.
When to Prune Your Bigleaf Hydrangea
Timing is everything. The safest window for pruning is immediately after the flowers fade in mid-to-late summer. This gives the plant plenty of time to grow new stems and set buds for the next year before winter arrives.
- Ideal Time: Late July through early August.
- Why Then? You can see the spent flowers easily, and the plant can focus energy on new growth.
- What to Avoid: Do not prune in fall, winter, or spring. Pruning then will remove the developing flower buds.
Step-by-Step Pruning Instructions
Follow these steps in order for the best results. Remember, the goal is to clean up the plant and encourage strong growth, not to drastically reshape it.
Step 1: Remove Spent Flowers
Start by deadheading. Locate the first set of plump, healthy leaf buds below the old flower head. Make your cut about half an inch above those buds. This neatens the plant and can sometimes encourage a second, smaller flush of blooms on reblooming varieties.
Step 2: Cut Out Dead or Damaged Wood
Next, look for any stems that are obviously dead (brittle, no green inside) or damaged by weather. Cut these stems all the way back to the base of the plant. Removing this material improves air circulation and prevents problems.
Step 3: Thin Out Old Stems
For an older, crowded shrub, you can improve its shape by removing a few of the oldest, thickest stems at ground level. Aim to take out no more than one-third of the total stems in a single year. This allows sunlight and air into the center of the plant.
Step 4: Address Weak Growth
Look for any very thin, spindly stems that are unlikely to support a large flower head. You can either remove these completely at the base or cut them back to a stronger, outward-facing bud to encourage sturdier growth.
What About Reblooming Hydrangeas?
Many newer Hydrangea macrophylla cultivars are “rebloomers.” These plants flower on both old wood (from last year) and new wood (from the current season). This gives you more flexibility. You can prune them lightly after their first bloom to encourage a second show, following the same steps above. If a harsh winter damages the old wood, they can still bloom on new growth.
Common Pruning Mistakes to Avoid
- Pruning at the Wrong Time: Fall or spring pruning is the most common reason for a lack of flowers.
- Cutting Everything Back: Never “shear” or cut all stems back by half. This removes the flower buds.
- Ignoring the Plant’s Shape: Always cut to an outward-facing bud to direct growth away from the plant’s center, preventing a tangled mess.
- Using Dull Tools: This can crush stems, making them vulnerable to die-back and infection.
What to Do If You Prune at the Wrong Time
Don’t panic if you’ve already pruned in the fall or early spring. The plant will be fine, but you may have fewer flowers for the coming summer. Focus on providing excellent care—consistent watering, a layer of mulch, and proper fertilizer—to help it recover and set buds for the following year. Sometimes, a missed bloom season is just a temporary setback.
Care After Pruning
After you finish pruning, give your hydrangea a little support to ensure it bounces back strongly.
- Watering: Water deeply if the weather is dry, as this helps the plant recover from the stress of pruning.
- Mulching: Apply a 2-3 inch layer of organic mulch (like shredded bark or compost) around the base. This keeps the roots cool and moist and protects them over winter, which is especially important for the fragile flower buds.
- Fertilizing: You can apply a balanced, slow-release fertilizer in late summer after pruning or in early spring. Avoid high-nitrogen fertilizers, which promote leaf growth at the expense of flowers.
FAQ: Pruning Bigleaf Hydrangeas
How do you prune hydrangea macrophylla in the UK or other mild climates?
The process is identical. The timing might be slightly later—often into August—because the flowering season may last longer in milder weather. The core rule remains: prune right after blooming finishes.
Can I prune my hydrangea macrophylla in spring?
It is not recommended. By spring, the buds are already formed and visible. Pruning then will directly remove the potential flowers. Only remove dead wood in spring if it’s clearly not leafing out.
My hydrangea has gotten very large. Can I cut it back hard?
You can, but know that you will sacrifice blooms for at least one season. For a major size reduction, prune one-third of the oldest stems to the ground each year for three years. This method is more gentle and maintains some flowers while you renovate the plant.
Why didn’t my hydrangea bloom this year?
Lack of flowers is rarely due to pruning alone. Other common causes include late spring frosts that kill buds, too much shade, excessive nitrogen fertilizer, or winter damage to the stems. Proper pruning just ensures you don’t add to the problem.
What’s the difference between pruning mophead vs. lacecap hydrangeas?
There is no practical difference in the pruning technique. Both are Hydrangea macrophylla and bloom on old wood. Follow the same steps for timing and method for both types.
Pruning your Hydrangea macrophylla doesn’t need to be a source of anxiety. By remembering the simple rule of “prune right after blooming,” you’ll avoid the biggest pitfall. Focus on cleaning up spent flowers, removing dead wood, and thinning for health rather than drastic shaping. With these easy steps, you’ll be rewarded with a healthier, more vibrant shrub that produces an abundance of those stunning blooms season after season. If you’re ever unsure, remember that less is often more when it comes to these beautiful garden classics.