Japanese maples – also known as thorn trees – are some of the most beautiful plants you can grow. With their leaves turning a stunning spectrum of deep purple to golden yellow and bright red in autumn, they are also the best trees for autumn colour. Although larger Japanese maples make delightful trees for shade, smaller specimens are some of the best trees to grow in pots. However, to get the most out of these glorious trees, gardeners need to prune them effectively – and at the right time if they want to be at their best.
Before gardeners start thinking about how to prune trees, they need to know when is the “best time” to do their gardening work.
The experts at PlantingTree.com said: “If it’s just a spin or two then go ahead and spare any time. For heavier pruning, trim your Japanese Maple in summer or winter.
“Winter is the best time to modify the tree structure and summer is the best time to thin the branches of your tree. If your tree is in full sun, especially in hot climates, avoid pruning in temperatures above 80 degrees Fahrenheit (26 degrees celsius) because the thin bark, which is no longer shaded after your thinning, is susceptible to scald Sun.”
After knowing when to prune these maple trees, it is then important to know the areas to prune. The experts said: “Pruning should aim to encourage the natural growth of your trees. There are five types of branches you should always consider removing from your Japanese maple.”
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1. Broken, dead or diseased branches
Remove any dead or dying branches with discolored or flaky bark with a clean cut. Gardeners should make sure they go slowly to prevent inadvertent chipping into a nearby branch.
The experts said: “These all have to go for obvious reasons. Cut them when you see them.” Broken, dead or dying branches can help stop the spread of disease, direct your tree’s nutrients and growth to healthy limbs and promote new, healthier growth.
2. Branches growing in or in the wrong direction
Branches that are growing inward or in the wrong direction should be removed. These include branches growing through the center of the tree, down an upright form, or branches growing up a weeping tree.
The tree experts said: “I personally like rogue branches growing in the wrong direction. They can be fun. So if you like them too, leave them alone; they will not harm a Japanese Maple tree. But ingrown branches can cause a lot of problems, so get rid of them.”
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3. Crossing branches
Crossing branches should also be cut as they often rub against each other or against the main stock which may interfere with their growth. The wounds created by friction allow insects and diseases to enter the tree.
The experts warned: “Crossing branches results in abrasion and damage to the bark and even the branches. This can encourage disease and pests. Cut off one of the branches.”
4. Narrow crotches
Narrow crotches are when two branches meet at an angle of less than 45 degrees. The gardening pros said: “Remove one of the branches to open up your tree and reduce the chance of breakage that can tear large patches of bark and cause other problems.”
5. Crowded branches
The experts explained: “When you have a crowded part of the crown or the entire crown is dense with branches and foliage, you will want to thin the branches to open up the crown. This will increase air flow and help your tree to be healthier.
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“Thin out by removing one branch out of every four or so. Create a cascading layered look that matches the natural look of the tree.”
When removing these branches, experts advised gardeners to use clippers or cleanly trimmed pruning shears for “best results”. They added: “When removing a whole branch, push back to the branch collar but do not insert it.
“Basically there shouldn’t be much of the branch left but you should never end up with the branch or connecting trunk.”
The tree gurus also shared some “no-numbers” when it comes to pruning. The first thing is to avoid pruning young trees “unless necessary”. They said: “Allow your tree to fully develop and grow on its own for 10 to 15 years before you do any serious pruning.
“Young trees often get long thin branches like whips. You may be tempted to cut off these long branches, but don’t. Be patient.
“They fill up and get side branches. If you cut them you are more likely to get more of the same type of branch.”
The pros also warned against overexertion. They said: “Don’t be too hasty. It is a one-of-a-kind clutch. Step back and take your time. You can always prune later. Do not remove more than one-fifth of the foliage or crown of a Japanese maple.”
Gardeners should not purchase a Japanese maple that grows too tall for your chosen location. The experts warned: “Trimming Japanese maps to control height is an unwinnable battle. It will only encourage faster growth and thinner, weaker branches.”