Japanese maple trees – also known as Acer palmatum – are some of the most beautiful trees you can grow. With their leaves turning a spectacular spectrum of deep purple to golden yellow and bright red in the fall, they are also the best trees for autumn color. While larger Japanese maples make delightful trees for shade, smaller specimens are some of the best trees to grow in pots. However, to make the most of these glorious trees, you must prune them effectively – and at the right time if you want them to put on their best show. ‘It’s important not to over-prune Japanese maples, so take time throughout the year to observe your tree and get to know it,’ says Pete Smith, arborist and urban forestry program manager at Arbor Day Foundation (opens in new tab). ‘Don’t prune your Japanese maple like other shade trees in your landscape. Rather, think of your specimen as a living sculpture you are creating in your garden. It should be pleasing to the eye throughout the year, and that begins with proper pruning, judiciously applied each year.’
When to prune Japanese maple trees – expert guide
Deciding when to prune Japanese maple trees is a common dilemma for gardeners. ‘The best time to prune Japanese maple trees is during late winter, before bud break,’ says Smith. ‘At this time of year, it’s easier to view the architecture of the tree; the way the branches are aligned and complement each other.’ However, if you have missed this window, it is not too late as they can be pruned at other times of year too. ‘Japanese maples can be pruned just about anytime,’ says Stuart Mackenzie, horticulturist, arborist and expert at Trees.com (opens in new tab). ‘I like to prune my Japanese maples at the end of summer to early fall. I can crown clean out any undesirable growth; weak attachments are easier to spot. The canopy can also be opened up for better air circulation. ‘At this time of year the tree will have recovered from any winter damage, and disease will be easily identifiable. There will also be less bleeding (sap running) now versus the springtime.’
When should you avoid pruning Japanese maple trees?
While in theory you can prune Japanese maple trees at any time of year, you should ideally avoid late spring and the height of summer. If you prune too late in the spring, you will remove a lot of new buds, which could limit the tree’s growth potential for the year. ‘Ideally wait until after the new growth has started, but before the leaves have fully unfurled,’ says Lindsey Hyland, founder of Urban Organic Yield (opens in new tab). ‘This ensures that the tree won’t lose too much of its energy reserves as it starts to grow again.’ However, if the tree is out of shape and really needs pruning, you should go ahead and sacrifice some new growth. Heavy pruning in the high summer heat can be problematic as it will minimize the tree’s shade benefits, and will also open up the tree to scorching heat. ‘Summers are typically stressful for Japanese maples thanks to hot temperatures and long periods of drought,’ says Bloomscape (opens in new tab)’s gardening expert Lindsay Pangborn. ‘Removing branches in summer also exposes leaves and bark that were previously shaded from the harsh rays of the sun and can cause scorch and leaf drop. ‘If you must prune in summer, aim to remove no more than one-quarter of the foliage and wait for a period of cooler temperatures and regular rainfall.’
Can you trim a Japanese maple in the summer?
While heavy pruning in high temperatures should be avoided, a light trim to keep the tree in shape can be beneficial during the summer. This is useful to ’touch up’ following a more thorough prune in the spring. However, avoid removing too many branches at this time. ‘This can lead to breakdown of live tissue and lead to disease or pests. You do not want to compromise the tree,’ says Mackenzie.
Does training Japanese maples influence when to prune them?
Japanese maple trees are some of the most ornamental trees, and many gardeners train them to keep them to a certain size or to grow in a certain shape – particularly when practicing bonsai. Japanese maples are one of the most recommended bonsai tree types. ‘Deciding when to prune Japanese maple trees is influenced by whether you train them,’ says Mackenzie. ‘Training for a desired effect of shape will determine when to prune and how to prune. The pruning can also help release hormones that will regulate growth and can actually slow growth down.’ You may also find that pruning Japanese maples is much easier if you first train them into the shape you want. ‘You can do this by selectively removing branches as they grow, so that the tree grows in the desired direction,’ says Hyland. ‘This will help to keep your Japanese maple looking good for years to come, and make the process of pruning a lot simpler.’
How often to prune Japanese maple trees
‘For regular landscape purposes, once to twice per year is a typical frequency for pruning Japanese maples. If you keep up on pruning, you shouldn’t need to remove much each year,’ says Pangborn. ‘It’s fine to prune once every few years instead, as this gives new branches more time to develop and may make it easier for the gardener to decide which branches to remove.’ If you perform a hard prune on your tree – which is best done in late winter – then it’s best to wait until the next year before pruning again, to allow the tree time to recover. ‘For speciality uses, like bonsai, it’s normal to prune much more frequently,’ adds Pangborn.
The experts’ tips for pruning Japanese maple trees
‘Japanese maples are known for their picturesque form. When pruning, step back frequently to look at the “big picture” and be sure you’re happy with the overall shape you’re creating,’ says Pangborn.‘When it’s time to prune, start by focusing on the branches that conflict with walkways or ones that compete with the central leader,’ says Smith.‘Cut back dead or diseased branches first – as well as ‘suckers’ (shoots that grow from the base of the tree) – then shape the tree as desired,’ says Hyland. ‘By doing this, you encourage healthy new growth and a strong structure for your tree.’‘When pruning main branches, always use the three-cut rule to avoid unnecessary damage,’ says Pangborn. ‘First, undercut the branch close to where the final cut will be. Second, working on the outside of your undercut, cut through the branch to remove the bulk of the weight. You’ll be left with a stub, which should be removed in the third step. Take care not to cut into the branch collar.’‘Never cut into the branch collar, as the response cells are in this location,’ adds Mackenzie. ‘If you cut too close or into the branch collar, recovery is slow or not at all. This can lead to heartwood decay and disease.’‘Avoid pruning more than one-third of the tree at a time,’ says Hyland.‘Pruning should always be done with sharp and properly sized tools,’ says Pangborn. ‘Pruners are good for branches smaller than the diameter of your finger, but for larger branches it’s best to use a pruning saw.
