When the sun starts shining brighter and the days stretch a little longer, it’s only natural to grab your gardening gloves and clippers.
May feels like the perfect time to get things in shape, especially after a long winter and a sleepy spring. But while you’re eager to trim back those wild branches and give your yard a tidy makeover, there’s something you need to know.
Not all plants appreciate a springtime haircut.
In fact, some plants suffer when pruned in May. They may lose their future blooms, invite pests, or even fall into long-term decline. What feels like a helpful chore could accidentally set your plants back. That’s why it’s crucial to know which green companions need a break from your shears this month.
Let’s dig into the plants that should be left alone in May and why your garden will thank you for it.
Lilacs
Lilacs are the kind of plant that brings a sense of calm and comfort to a garden. Their large, fragrant blooms fill the air with a sweet scent and attract bees, butterflies, and anyone who walks nearby. After months of gray skies and chilly mornings, lilacs feel like a promise fulfilled.
It’s tempting to tidy them up in May when you see overgrown branches or blooms starting to fade. But pruning lilacs too soon can be a major misstep.
These shrubs bloom on old wood, which means that next year’s flower buds start forming not long after this year’s blossoms disappear. If you cut the branches in May while the flowers are still present or just finishing, you’re likely removing those forming buds. You won’t see the damage right away, but next spring your lilac may come up full of leaves and completely bare of blooms.
The best time to prune a lilac is right after it finishes flowering. That’s usually late May or early June, depending on your location and the weather. Once the blossoms are gone, you can safely remove spent blooms and shape the shrub without risking next year’s display.
There’s no need to prune lilacs every year. In fact, constant trimming can weaken the plant and reduce flowering over time.
Most lilacs only need light pruning for shape or to remove dead or damaged branches. If the bush has become too dense or tall, you can thin it out carefully, cutting only a few of the oldest stems down to the ground to encourage new growth.
Be gentle, be patient, and let your lilac follow its natural rhythm. A little restraint in May can lead to a much more beautiful result next spring.
Hydrangeas
Hydrangeas are showstoppers. Whether they’re in soft pastels or vibrant blues and purples, their round clusters of flowers add a burst of color to any garden. They often steal the spotlight in midsummer, and they’re favorites for bouquets, hedges, and shady corners.
But hydrangeas are also easy to mess up if you don’t understand their timing.
Many gardeners are surprised to learn that hydrangeas don’t all follow the same rules. Some bloom on old wood, while others bloom on new growth.
The problem is that pruning at the wrong time can remove the stems that would have flowered later in the season. It’s like cutting off a promise before it has a chance to show itself.
If your hydrangea blooms on old wood, such as the common bigleaf or oakleaf varieties, those buds are already forming by late spring. Pruning in May can mean accidentally removing all the growth that would have turned into flowers by summer. Instead of full, blooming plants, you’re left with healthy leaves and empty stems.
Even for varieties that bloom on new wood, like panicle or smooth hydrangeas, May is still not the best time to prune. These types respond better to pruning in late winter or early spring before new growth begins. Pruning too late in spring can stress the plant and lead to smaller blooms or an uneven shape.
So how can you tell what kind of hydrangea you have?
Look at the shape of the leaves, the structure of the stems, and when it usually blooms. If you’re not sure, it’s safer to hold off on pruning until after it flowers. Once the blooms fade, you can shape it gently and remove spent flowers, but avoid heavy cuts.
Hydrangeas are forgiving in many ways, but not when it comes to timing. A little knowledge and patience go a long way.
By skipping the clippers in May, you give your hydrangeas the best chance to bloom beautifully in the weeks ahead.
Forsythia
Forsythia is one of the first signs of spring. Its bright yellow flowers burst out before most trees have even grown their leaves.
A mature forsythia shrub in full bloom looks like a fountain of sunshine, spilling color into the landscape just when it’s needed most.
Because forsythia grows quickly and tends to get a bit wild, many gardeners reach for the clippers in May, hoping to control its shape. But if you prune at the wrong time, you’re setting yourself up for disappointment.
Like lilacs, forsythia blooms on old wood. That means the stems that produce flowers each spring were actually formed the previous summer.
When you prune in May, right after or even during blooming, you risk cutting off next year’s flower buds before they’ve even had a chance to form. It’s an easy mistake to make, but it can result in a year with little or no color.
The best time to prune forsythia is right after the blooming period ends. This gives the plant enough time to grow and set new flower buds throughout the summer. If you wait too long, those buds won’t form, and you’ll miss out on next spring’s show.
It’s also important to remember that forsythia doesn’t need to be heavily pruned every year. A gentle trim to shape the plant and remove any dead or crossing branches is often enough.
If your shrub has become overgrown or too dense, you can rejuvenate it by cutting a few of the oldest canes down to the ground, but always do this right after blooming.
When handled with care and patience, forsythia rewards you with a cheerful and reliable burst of color each year. All it asks is that you hold off on pruning until the right moment has passed.
Boxwood
Boxwood is a favorite for formal gardens, tidy hedges, and sculpted shapes. Its small, glossy green leaves and dense growth make it perfect for clean edges and creative designs. You’ll often see it lining walkways or framing flower beds in neat, low rows.
Because of its fast-growing nature and well-known ability to handle shaping, boxwood often gets pruned too often and at the wrong time. May feels like a good month to tidy up, but cutting boxwood in late spring can lead to some serious problems.
One of the biggest risks is sunscald. When you prune in May, you remove outer layers of leaves that have been shading the inner parts of the plant.
This sudden exposure to bright sunlight can scorch the delicate inner foliage, turning it brown and damaging healthy growth.
Another issue is pest and disease vulnerability. Fresh cuts made in late spring or early summer are an open invitation to insects and fungal problems. Boxwood blight, in particular, is more likely to take hold when the plant is stressed and wounded. Pruning during warm, humid weather increases this risk.
The best time to prune boxwood is in late winter or very early spring, just before new growth begins. This allows you to shape the plant while it’s still dormant and gives the cuts time to heal before pests become active.
If you need to touch up your boxwood in summer, only do light trimming and avoid cutting during extreme heat or high humidity. Always use clean, sharp tools and avoid removing too much at once.
With the right timing, boxwood will stay full, healthy, and green all year long. Skipping the May trim gives it a stronger foundation for summer and helps it resist problems down the road.
Salvia
Salvia is one of those plants that looks tough but can be surprisingly sensitive. With its tall spikes of purple, pink, blue, or red flowers and its ability to draw in pollinators like bees and hummingbirds, salvia is a must-have in many sunny gardens. It thrives in heat, handles dry conditions well, and comes back strong year after year.
But if you’re thinking about cutting it back in May, think again.
Salvia may look like it’s ready for a trim when early growth starts to look floppy or when the stems seem a bit unruly. However, early pruning can throw the plant off balance.
The stems may still be developing strength and structure in May. Cutting them too soon removes the energy the plant needs to push out its first strong wave of blooms.
Most perennial varieties of salvia, such as Salvia nemorosa or Salvia x sylvestris, begin flowering in late spring or early summer. If you prune them in May, you could delay flowering or reduce the number of blooms.
In some cases, early cuts can cause the plant to produce weak stems that flop over as they grow taller.
The best approach is to wait until after the first big wave of blooms is finished. At that point, usually in early to mid-summer, you can shear the plant back by about one-third.
This encourages fresh growth and a second round of flowers later in the season. It also keeps the plant looking tidy and full rather than leggy and worn out.
For young plants or those that seem slow to start, patience is key. Let them get fully established before you consider any shaping or cutting.
With a little timing and care, your salvia will reward you with months of color and activity from visiting pollinators.
Final Thoughts
Gardening can be exciting in May. Everything is waking up, and it feels like the perfect time to get things in order. But when it comes to pruning, it’s just as important to know when not to act.
Plants like lilacs, hydrangeas, forsythia, boxwood, and salvia all have specific rhythms. Trimming too early can interrupt blooming cycles, open the door to pests, or simply take away the beauty you were hoping to enjoy later in the season.
Instead of rushing in with the clippers, take a moment to observe. Notice which plants are still blooming, which ones are forming buds, and which just need time. Gardening is about working with nature, not rushing it.
By giving your plants the space and time they need now, you’re setting up your garden for stronger growth, better flowers, and a more vibrant display through the seasons. Sometimes, the best gardening move is to simply wait.