Written by Dale Richardson - Updated: June 23, 2023
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Acer (AKA maple) trees come in a wide variety of sizes and colours. Some fit into pots, while others are large enough to be the centrepiece of your garden. Regardless of their size or shape, they can come with their own share of problems. If you're trying and failing to grow a maple, you've come to the right place! We've got a full list of the most common Acer tree problems - and perhaps more importantly, how to fix them!
The most common Acer tree problems are various diseases, pests, improper pot size (if you chose to pot your tree), poor nutrient supply, and bad soil.
Wow! That was a mouthful. Let's get into it, shall we?
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There's a lot to know about what can afflict maple trees when growing - especially if you're using a variant that's not native to your climate. In Britain, Japanese maples are wildly popular for their beautiful colouring and manageable size. Unfortunately, Britain isn't exactly the most welcoming place for non-native plants. This means that knowing how to spot issues early will mean the difference between life and death for your Acer tree.
Let's start with basics first - we'll move onto diseases in time, as that'll be its own little list.
Rabbits and squirrels (really rodents in general) are the most common small critters that will cause issues with your maple. You'll notice damage to the bark and branches first, though don't worry - this won't actively kill your tree, per se. You'll eventually end up with an ugly tree, but at least it'll be living, right?
This is because rodents' teeth never stop growing - that means that they need to gnaw on something hard to file their teeth down. It seems like they enjoy the taste of maple more than other trees - though don't be fooled; nothing is safe from these little guys. Luckily there are a few things you can do to get them to back off your prized tree:
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If you've got an Acer that's potted, this is an important section that you should read. Have you noticed your potted Japanese maple starting to struggle to stay alive? Take a look at your potting situation - how big is the pot in comparison to the tree's root system? Does the pot have drainage holes? These are vital things to know. If you're curious for more information, check out my guide on common potted olive tree problems - we talk for a while about how to choose a proper pot, and most of that carries over.
The general rule of thumb is that you need a pot at least twice as big as the tree's root system. This also means that you'll need to repot every four years or so as the tree, and its roots, grow. The other vital part of your pot is that it has drainage holes. A pot with no drainage will drown your tree's root system and can result in root rot, which we'll talk about further down.
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Just like animals need a good balance of nutrients to grow strong and healthy, trees and plants are the same - though you likely know that already. It's important to match your soil to the type of plant you're trying to grow, especially if it's not native to your climate. Japanese maples, for example, are (obviously) native to Japan, meaning they love slightly acidic, sandy soil that retains water well and drains easily.
A lot of gardeners swear by using loam-based compost for growing Acer trees - potted or not. This will provide a good amount of nutrients and allow excellent drainage.
We're going to group mulch in with soil, as it's vital to growing most trees. In case you didn't know - mulching your tree's "neighbourhood" will keep it much happier than using basic soil. Using mulch or compost around the tree (without actually getting up next to the base of the tree) will help maintain moisture and provide a little boost of growth potential. It'll also help avoid issues like leaf scorch or case-hardening around the roots.
This is more important if you're potting the tree, though the general guides still apply to planted trees. Direct sunlight for Acer trees, especially in hot climates, is generally a no-go. Finding a spot that's sheltered from high wind and won't expose the tree to too much sun is super important.
If you're worried about temporary weather conditions, consider trying to install a windbreak around your tree. For freezing conditions, do not bring the potted tree inside - most experts agree that the sudden change in temperature is worse for the tree than our solution.
The best way to protect an Acer tree from frost damage is to wrap it in insulating material. Even something as simple as a large cardboard box with some wax or plastic on the outside to prevent it from fading with water will do here.
First things first - pruning is not generally necessary to the overall health of your Acer tree. Pruning is usually only done for aesthetic purposes, occasionally to help treat a disease or a dying section of the tree.
If you feel that you do need to prune the tree for any reason, the best time to do so is generally late summer or early autumn. Pruning outside of this time can cause bleeding which can cause further damage to the tree. If you're an experienced gardener, then root pruning won't be new to you, but in case it is, let's discuss for a second.
Root pruning is exactly what it sounds like - you're pruning the roots of the tree. Generally, this is done when replacing soil ( which yes, you need to do ). If you spot roots that are dry, hardened, and seem dead - prune them! If you're not sure, though, it's generally best to at least consult a pro to see if you'll harm the tree before continuing.
Now, this is the fun part! This is the section where we talk about various bugs and infections that your Acer tree problems can stem from. Let's get into it, shall we?
Depending on your climate, these bugs will vary - but there's a few that seem to love maples that you'll want to keep an eye out for. There are aphids, mites, pear thrips, and scale insects. Luckily, there are a lot of treatments for these guys:
This comes in a lot of forms, though the most common in the UK is phytophthora. It can be spotted by cankers and mushroom-like growth near the base of the tree. They'll generally appear near the root system, as that's what it actively attacks. You'll also notice branches starting to die and foliage beginning to wilt and become more sparse. The only way to treat this is to prevent it in the first place by taking proper care of your tree.
If your tree develops root rot, it's likely time to call it for that tree. Learn from your mistakes - allow better drainage and adjust your watering schedule in heavy rain.
This is easily spotted by specific parts (or even one side of the tree) yellowing, losing leaves, and stunted growth. It's caused by a fungus in your soil and is extremely common with most subspecies of Acer. You'll notice it in late summer, following extremely hot and dry stretches of time.
The best, and really only way, to treat this is with proper watering, fertiliser, and shade. Try to use a low-nitrogen, high-phosphorous fertiliser and prune dead or dying branches as soon as you see them. As this is a fungus, it can spread, so be careful.
If you really want to dive into treating the problem, you can solarize your soil. This is done by tilling and wetting the top 15 cm of soil, covering it with a clear plastic tarp, and burying it under roughly 8 cm of soil. Place it in the best area to get constant sunlight, as you're essentially drying and burning the fungus out. This is not a guaranteed fix. Often, verticillium wilt is incurable and fatal to most plants.
All Acer trees are susceptible to this, though Norway and Japanese maples are the most vulnerable. This is incredibly common in moist, humid environments and generally is more of an inconvenience than a death sentence.
Powdery mildew can be spotted by white, powdery tops of leaves and browning undersides. It can be removed by hand, as well as using chemical fungicides. You can even use neem oil for this - as I said above, neem oil is awesome for gardening. A good DIY fungicide is:
The main symptoms of honey fungus are decaying roots and fungal growths, meaning it can easily be mistaken for root rot. You'll notice toadstools on the stumps of the tree, along with growth between the bark and wood, and small, pale leaves.
Leaf scorch can be caused by either poor weather (hot, dry wind and sun, or frost with waterlogged soil), or bacterial infection. Leaf scorch of any form can be spotted by drying leaves with browning veins and edges. You can also (depending on the type) expect to see red or yellow bands between green and brown patches along the leaf's surface.
To treat (and prevent) leaf scorch:
Acer (maple) trees are absolutely beautiful, and unfortunately, rather prone to disease and pests. Luckily, Fraffles did the legwork for you and brought you this absolute chunker of a list for all of your Acer woes. Whether it's a small Japanese Acer in a pot or a massive Canadian Maple in your yard - you should be set to handle anything mother nature throws at you.
Be sure to check out our other gardening work, as there's a lot of overlap for treatments of various diseases that affect your garden. And we're here to help, so be sure to check back with more questions in the future - we'll be waiting.
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