Pruning Acer Trees and Shrubs – When and how to prune Japanese Maples

Pruning Acer Trees and Shrubs – When and how to prune Japanese Maples

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Worth the centrepiece position in any garden and one of my personal favourites, Acer trees, also known as Japanese maples possess an understated elegance throughout the seasons. Their colourful foliage in spring together with bare branches in winter always offers visual interest to many.

Regardless of whether you have a smaller variety like Acer palmatum or Acer platanoides, which is a larger variety; occasional pruning is essential in maintaining the shape and size of many varieties and most respond very well to a good pruning, especially once there established.

Acers, whether it’s the taller tree varieties or more compact smaller bush varieties don’t need to be pruned but if you want to maintain a certain aesthetic, you need to understand when and how to prune them. This article offers simple tips that will make owning and maintaining Acer trees and shrubs more straightforward.

Japanese Maple tree maintained with light pruning

When is the right time to prune acers (Japanese maples)

A mature Acer tree is stronger and can handle pruning without developing any problems. Pruning Acer trees should be done when the tree is dormant, which is typically around November to January but a few weeks on either side of these months won’t do any harm either.

At this time, the tree has no leaves making it easier to access the branches. The idea is to remove any dead or diseased branches while cutting back to the desired shape.

Another reason to prune these trees in winter is that sap production is at its lowest. Pruning at the wrong time may cause the tree to over bleed sap and lose its vigour.

If limbing up on established trees, do it in stages

Something else worth considering if you choose to cut the lowest branches off an established tree, you will have to do it in stages. Also known as limbing up, this process allows the trees to recuperate for a few days before removing more branches.

Cutting all the lower branches at once will increase the tree’s risk of infection and decay. Furthermore, the lower branches are more established therefore removing them all at once will cause the plant stress and decrease the tree’s vigour.

If your tree is mature make sure to separate the branches to maintain a neat aesthetic look. Carefully prune any branches that stray into others whether below or above. These are usually branches that are rubbing against each other which is lead to issues later on.

Another point to consider is removing some of the small lateral branches as this helps reduce unwanted bulk while maintaining lush foliage.

Acer tree with autumn colour

How to prune acers

When pruning acers, always try to prune to just above an outward-facing bud. Also, use a clean sharp pair of secateurs or loppers. For larger trees, you may need to use a pruning saw.

A few pruning tips

There are common mistakes that I have learnt to avoid when dealing with Acer trees. Things to keep in mind include:

  • Avoid removing more foliage than required from a single branch. You can remove less than ¼ of the foliage from the branch to avoid the intake of fewer nutrients.
  • Use sharp secatuers or loppers to avoid uneven surfaces on the wound that might encourage pests and diseases.
  • Do not prune branches that are more than half the diameter of the main parent stem.
  • Pruning more than 20% of the crown will affect the tree’s vigour and appearance by encouraging unorganised new growth.
  • Avoid cutting away the wispy branches until they are matured. This way the tree has enough room to present a well-designed framework for the shape you want.
  • Do not prune too close to the stem, give adequate room of about 0.5cm. This gives the tree enough time to heal and avoid infestations.

Acer trees can live for more than a century if the conditions are right which is why you often see them in old stately gardens. A 10-year-old Acer tree usually produces new growth that is thin and lacking side branches. While at this stage the thin growth may look unattractive, it is better not to prune.

You should let the growth mature to establish scaffold limbs for better shaping. Cutting off the new growth too soon will only lead to wispier branches and encourage the tree to grow taller. If you are trying to restrict the height of the tree, prune once the plant is more mature and more established.

Read next: How to prune pieris to rejuvenate old woody shrubs

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