Your May Pruning Guide: What to Cut Back Now for Glorious Summer Growth – and What to Leave Alone
A go-to guide for all your May pruning
Knowing what and what not to prune in May mostly comes down to when a plant flowers. It sounds simple, and it often is. When it comes to shrubs, trees, and climbers, if they flower in spring and have finished, prune them. If they are still flowering or yet to reach their potential, keep those pruning tools away.
That is a very general overview of plants to prune in May, but it applies to many plants. In addition to pruning spring-flowering plants that have finished blooming, you can also cut back perennials before they bloom for a better display come summer. Plus, May is also an opportune time to trim evergreens.
Article continues belowPlants to Prune in May
Spring-Flowering Shrubs
One of the key plants to prune in May is spring-flowering shrubs. The beauties have done their flowering for the year, and now is the time to show them some love so they put on a repeat performance next year.
Shrubs like forsythia, lilac, azalea, rhododendron, Mexican orange blossom, weigelia, and kerria all want pruning right after they have finished blooming. Once the flowers fade, it is time for action. That action is justified, as these shrubs flower on old wood. So the growth you encourage by pruning this month carries next spring’s buds and flowers.
Spring pruning of these flowering shrubs predominantly involves removing dead, diseased, damaged, and crossing branches. Always cut back to a bud or to the base to encourage fresh, productive, new growth. For older shrubs, remove one or two of the oldest stems, but no more than one-third.
Herbaceous Perennials
There is a pruning method known in the UK as The Chelsea Chop, where perennials are cut back in May to coincide with the RHS Chelsea Flower Show.
A range of the best perennials can be chopped by a third, and there is a real method to the madness. This pruning technique encourages bushier growth, less flopping during summer, and more flowers as the plant develops lots of side shoots.
Perennials in your flower beds that may benefit from this pruning technique in late May include helenium, phlox, coneflower, black-eyed Susan, sedum, aster, yarrow, hardy geraniums, and monarda. If you are nervous about trying this out, you can cut certain clumps and not others, or even do half of a clump and leave the rest.
The method is easy. Use a pair of pruning shears or hedge shears and chop back the perennial by between a third and a half.
Evergreen Hedges
May is a good month to trim evergreen shrubs and hedges, but lightly. After the frosts have ended, it is a perfect time to tidy and shape hedges and shrubs, including boxwood, yew, cypress, and privet.
Spring trimming removes winter damage and stimulates fresh new growth. Cut back up to 20%, and the hedge will bounce back with fast growth to cover any pruning cuts and keep it looking lush for summer.
Sharp pruning tools are a must for pruning evergreen hedges. Blunt tools will bruise leaves or cause a jagged tear. This leaves an unsightly hedge afterwards, and can be avoided by taking a moment to sharpen your tools before heading out.
This can be done quickly with a pocket-sized tool sharpener, like this garden tool sharpener at Amazon.
Early Climbers
Just like spring-flowering shrubs, early-flowering climbers should be pruned after they have finished flowering.
That includes early types of clematis, such as clematis montana. Once early clematis, a group which also includes C. alpina, C. macropetala, and C. cirrhosa, finish flowering, overgrown stems benefit from being untangled and cut back to a pair of healthy buds.
Other climbers to prune in May include abelia, akebia, winter-flowering lonicera, and any wall-trained pyracantha.
Another essential May job for climbers is tying in new growth. The stems are growing rapidly in spring, so take time to train new shoots to their climbing plant supports. Use soft ties to prevent damaging stems – I have often used flexible ties like these at Amazon to tie in climbers safely.
Spring Bulbs
This task divides opinion in the horticultural world, so we’ll leave it up to you whether you do it in May. All in all, there are benefits to deadheading spring bulbs, but it is not always an essential task.
After the flowers have faded from your daffodils, hyacinths, or tulips, deadhead them to focus the energy into the bulb rather than into producing seeds. This can make a difference to next year’s display.
Remove the old blooms, but don’t cut back the foliage. The stems and leaves should be left for at least six weeks after flowering to keep photosynthesizing and feeding the bulb. Only cut the foliage once it has fully died back naturally.
You see some gardeners tie the foliage into knots. Do not do this, as it actively limits the sunlight and restricts photosynthesis. For the strongest flowers next spring, cut the blooms and don’t touch the foliage.
Shop Pruning Tools
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These adjustable hedge shears have eight-inch hardened, precision-ground steel blades and shock-absorbing bumpers for pain-free trimming of shrubs or hedges.
Plants to Never Prune in May
Plants That Are Blooming
In May, there can be spring-flowering shrubs and trees still in bloom. It is a massive waste to prune these while they are still flowering.
The same can be said for any plants that flower in spring but are yet to reach their full blooming potential this year – you risk removing flowering buds if you trim now.
Any plants in your yard that flower in spring will flower on old wood, so the rule to remember is that you prune them after they finish blooming for the year.
Spring-Flowering Perennials
Lots of perennials burst into color in spring, providing early color in gardens. Don’t be in too much of a rush to prune back these spring-flowering perennials, as it can impact next year’s display.
The likes of bleeding heart, columbine, and hellebore are best left to die back naturally. Doing so gives the plant lots of time to store energy for next year’s display.
In the case of columbine and other self-seeders, removing the blooms too soon reduces the chances of spreading. While this may be ideal for some gardeners, others may like new flowers to appear next year.
Bleeder Trees
Some trees come with a reputation for bleeding sap in early spring. Indeed, the likes of maple, birch, beech, elm, and walnut trees are coined ‘bleeder trees’ for their tendency to ooze sap from pruning cuts at certain times of year.
Spring is when the sap is rising at its peak, and pruning them this month will not only be messy but also risk leaving the trees stressed and susceptible to pests or diseases. It is better to hold fire and prune these trees in midsummer.
Hedges With Nesting Birds
May is prime bird nesting season, so it is recommended to pause hedge-cutting to avoid disturbing them.
The Migratory Bird Treaty Act makes it illegal to disturb or destroy active native bird nests, and this time of year is when many birds will be building or settling into their nests.
As hedges and shrubs can be prime real estate for birds due to the shelter and protection they offer, any pruning that disturbs these nests can land you in trouble and see you face potential penalties or fines.
There is a strong likelihood of frequent storms across some regions of the US during May. If you live in such affected areas, it is beneficial to prepare by looking out for and pruning tree branches that could come down during storms. Once the worst of the weather has passed, check again for any branches or stems that look precarious and remove them as required.
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