Did you know that there are some bushes you should never prune in the late summer or fall? That’s because for many shrubs and bushes, late pruning risks losing their flowers for next year. And even worse, pruning at the wrong time can also leave them more vulnerable to winter damage as well!
Although late summer and fall can seem like the perfect time to tidy up overgrown bushes and shrubs, it can spell big trouble for plants that bloom on old wood. Unlike shrubs that produce flowers on new growth each spring, old-wood bloomers form their flower buds months in advance.
In fact, many of these bushes begin setting next year’s flower buds shortly after they finish blooming. By the time late summer and fall arrive, those tiny buds are already sitting on the branches, waiting patiently through winter to burst into bloom the following spring.
Bushes You Should Never Prune In Late Summer Or Fall
The Big 5
Unfortunately, when you trim those branches back in August, September or fall, you aren’t just removing leaves and stems. You are also cutting away next year’s flowers! With that in mind, here is a look at five popular flowering bushes you should avoid pruning in late summer and fall – including lilacs, rhododendrons and azaleas, oakleaf hydrangeas, and forsythia – along with when and how to prune each one instead.
#1 Why To Never Prune Lilac Bushes In Late Summer or Fall
Lilacs are one of the most common shrubs to accidentally prune at the wrong time. After blooming in spring, their bushes can quickly become large, unruly and even a bit unsightly. That often makes late summer and fall pruning tempting. But resist the urge to grab the pruners!
Lilacs bloom on old wood. Almost immediately after their spring flowers fade, the plant begins preparing for the following year’s blooming cycle. By summer, many of those future flower buds are already developing on the branches.
If you cut a lilac back in late summer or fall, you can easily remove a large percentage of those buds. The shrub will usually survive the pruning just fine, but you may end up with lots of green foliage and very few blooms the following spring.
The best time to prune lilacs is immediately after they finish flowering. This gives the plant plenty of time to produce new growth and develop flower buds before winter arrives.
When pruning, remove spent blooms and any dead, damaged or crossing branches. For older, overgrown lilacs, you can also remove a few of the oldest stems near ground level each year. This helps rejuvenate the shrub without severely stressing it.
#2 Rhododendrons & Azaleas
Although rhododendrons and azaleas are technically two different groups of plants, their pruning requirements are extremely similar. And when it comes to late summer and fall pruning, both should be left alone.
Rhododendrons and azaleas put on their colorful flower displays in spring and early summer. Soon after those flowers fade, the plants begin forming buds for the following year’s blooms.
By late summer, the flower buds can often be seen at the tips of the branches. Unfortunately, trimming or shaping the bushes at this point can remove those buds in seconds.
The safest time to prune both shrubs is shortly after flowering ends. Light shaping can be done at this time, along with removing dead or damaged branches.
Avoid heavy pruning whenever possible. Rhododendrons and azaleas generally look their best when allowed to maintain a more natural shape rather than being repeatedly sheared into tight forms.
There is another reason to avoid pruning these shrubs late in the season. Pruning can encourage tender new growth. If that growth doesn’t have enough time to harden off before freezing temperatures arrive, it can suffer winter damage.
#3 Oakleaf Hydrangeas
Hydrangeas can be confusing when it comes to pruning because not every variety flowers the same way. Some hydrangeas bloom on new wood and can tolerate pruning in late winter or early spring. But oakleaf hydrangeas are different. They produce their flowers primarily on old wood, which means late summer and fall pruning can eliminate next year’s blooms.
Oakleaf hydrangeas are easy to recognize by their large leaves that resemble those of an oak tree. In addition to their beautiful summer flowers, their foliage often turns gorgeous shades of red, burgundy and purple in fall.
Once an oakleaf hydrangea finishes blooming, it begins developing buds on the stems that will produce flowers the following year. Cutting the shrub back in fall removes those stems – and the blooms along with them.
If your oakleaf hydrangea needs shaping, prune it shortly after flowering. Remove only what is necessary to control its size and shape. In fall, simply allow the shrub to go dormant naturally. In fact, leaving its branches and fading flowers in place can provide wonderful winter interest in the landscape.
Why To Never Prune Forsythia Bushes In Late Summer Or Fall
Few shrubs announce the arrival of spring quite like forsythia. Its branches become covered in brilliant yellow flowers, often before many other plants have even begun to wake up. But if you want that huge display of yellow flowers every spring, never prune your forsythia in late summer or fall.
Forsythia blooms on wood that grew during the previous season. Once its spring flowering period ends, new branches begin growing. Those branches then develop the flower buds that remain dormant through winter. By late summer, next year’s show is already largely in place.
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Unfortunately, pruning forsythia in fall removes the very branches that are holding those flower buds. You might end up with a beautifully shaped shrub going into winter – but one with very few yellow flowers the following spring.
The ideal time to prune forsythia is immediately after it finishes blooming. Rather than simply shearing the outside of the bush, remove some of the oldest and largest stems all the way to the ground.
This encourages fresh growth from the base and helps keep the shrub open, healthy and blooming strong year after year.
#5 Bigleaf Hydrangeas
Oakleaf hydrangeas aren’t the only hydrangeas that can suffer from late-season pruning. Traditional bigleaf hydrangeas – including many mophead and lacecap varieties – also need special care.
Many classic bigleaf hydrangeas form their flower buds on old wood. Those buds develop during summer and remain on the stems throughout fall and winter. Prune those stems back in fall and you may be cutting away most or all of the following year’s flowers.
This is one of the most common reasons gardeners have a hydrangea that grows beautifully but refuses to bloom. The plant isn’t necessarily unhealthy – its flower buds may simply have been removed during pruning.
For old-wood blooming bigleaf hydrangeas, prune shortly after flowering if pruning is needed at all. Dead or damaged wood can be removed when identified, but major shaping should be done carefully.
There are now many reblooming hydrangeas that flower on both old and new wood, so knowing the variety you grow can make a big difference. When you aren’t sure what type of hydrangea you have, the safest option is to avoid cutting it back in fall.
What Can You Prune In Fall?
That doesn’t mean you have to completely ignore your shrubs in the fall. Dead, broken or badly damaged branches can generally be removed whenever necessary. If a branch has been damaged by a storm or is creating a safety issue, there is little reason to leave it in place simply because it is fall. And when you do prune – always use sharp pruners to avoid more damage! Affiliate Link: Fiskars Bypass Pruning Shears, 5/8″ Cut Capacity Garden Clippers
The key is to avoid major shaping, shearing and size reduction on spring-flowering shrubs. Instead, make a note of which plants need attention and tackle them at the proper time after they flower next year. Not only will the shrubs recover faster, you will also get to enjoy all of the blooms they have spent months creating!
Here is to knowing which bushes to never prune in late summer or fall – and to more blooms and healthier bushes next summer! Happy Gardening, Jim & Mary.
The Farm @ Old World Garden
Jim and Mary Competti have been writing gardening, DIY and recipe articles and books for over 16 years from their 46 acre Ohio farm. The two are frequent speakers on all things gardening and love to travel in their spare time.
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