Pruning a Japanese maple: get it right with this expert advice

Pruning Japanese maples, otherwise known as acers, isn't one of those essential tasks that you have to tick off your annual gardening calendar. In fact, one of the reasons we love these trees so much is that they don't need much maintenance at all. But, done correctly, a trim now and then can neaten up their shape, let more light through, and make them better suited to the conditions of your backyard.

Any gardener can learn how to grow acers, no matter how big their plot. From smaller trees in patio pots to large, impressive specimens, their color and form will always add interest to a space. And if your plot is graced by one of these beauties, these simple tips on how to prune it are sure to come in handy to help it truly flourish.

4 top tips for pruning Japanese maples

Ned Cromack, arborist and founder of Bristol Tree Medic, is a fan of these ornamental trees, explaining how they have an amazing range of colors and are perfect for creating dappled shade. He shares his top tips on pruning them for the best results.

1. Start with a plan

Ned says that it is important to think of the overall goal before you pick up your best secateurs or a hand saw. Japanese maples are relatively slow-growing, so make sure you have a plan before you start chopping away at branches.

'The natural and most beautiful shape acers can take is really wide-spread, with long branches,' says Ned. 'You can encourage that by not cutting the ends of them.' Instead, plan to cut dead wood out and busy internal branches to allow more light to penetrate through. The RHS agrees, explaining how pruning should be kept to a minimum 'as the most graceful shape comes from a tree that has been allowed to develop fairly naturally.'

Sometimes, however, you may wish to reduce the size of your acer – for instance, if it's growing too close to a fence or the wall of a house.

2. Use the right tools

'You want the cuts to be as clean as possible,' says Ned. 'I would recommend anvil secateurs for pruning a tree. Bypass ones are meant for plants – for cutting through weaker fibers. 

'Anvil ones will slice the branch, whereas bypass ones will tear it,' Ned continues. 'If you're pruning larger branches or dead branches, use a hand saw.'

It's also good practice to ensure you've sharpened and cleaned your pruning shears or other tool you're using before you begin, to avoid spreading any diseases to your acer.

3. Cut each branch back to a fork, if possible

Whether you need to take a bit of length off the ends of a few branches or are simply thinning out the canopy, you will need to bear in mind the optimal pruning points, as with any backyard tree. 

'When shortening branches, pruning back to where another branch is coming from will be better for the shape of the tree,' says Ned. 'Don't just lop a branch halfway down.' Snipping branches at random will cause them to shoot up two weak stems. This can create a feathery edge to your tree which needs constant maintenance.

'If you have to, take the branch back to a bud or a dormant bud,' continues Ned. 'However, if you can see a fork of two branches, it's better to take one out – whichever one is longer. The other one will take dominance and carry on growing, and you will get a much more natural shape.' 

4. Don't overdo it

If you're thinning your tree, make sure you don't overdo it. This can make each branch look like a lion's tale, says Ned. This goes against the natural way the tree wants to form, and can make it more susceptible to wind damage. What's more, taking too much out can actually make it 'panic grow' and make the internal branches grow back quicker and bushier than they were to begin with.

When pruning Japanese maples and other trees, a really good rule of thumb is to never take off more than a third of the canopy, says Ned. 'Little and often is better, there's no rush.

'Get on it early before it gets too big, or if it's already big, do it gradually,' he adds.

And once you've finished pruning your acer, remember to make use of the woody waste – our guide explains how.

When is the best time to prune a Japanese maple?

There's another crucial element to learning how to prune Japanese maples correctly, and that's to do it at the right time of year. 

According to the RHS, the best time for pruning acers is when they are dormant – from late fall to late winter. If you cut them at other times in the year, they will bleed sap which will weaken the tree.