Acer palmatum or Japanese Maples are some of the most versatile and compact little trees you can plant in your garden and better still, they’re really easy to look after. Just follow our growers’ acer tree care tips and they’ll thrive in any spot, providing you with dazzling color for many years.
I. Appearance and Characteristics
Acer palmatum, commonly known as Japanese maple, palmate maple, or smooth Japanese maple (Korean: danpungnamu, 단풍나무, Japanese: irohamomiji, イロハモミジ, or momiji, (栴), is a species of woody plant native to Korea, Japan, China, eastern Mongolia, and southeast Russia. Many different cultivars of this maple have been selected and they are grown worldwide for their large variety of attractive forms, leaf shapes, and spectacular colors.
Acer palmatum is deciduous, with the growth habit of a shrub or small tree reaching heights of 6 to 10 m (20 to 33 ft), rarely 16 m (52 ft), reaching a mature width of 4.5 to 10 m (15 to 33 ft), often growing as an understory plant in shady woodlands. It may have multiple trunks joining close to the ground. In habit, its canopy often takes on a dome-like form, especially when mature. The leaves are 4–12 cm (1+1⁄2–4+3⁄4 in) long and wide, palmately lobed with five, seven, or nine acutely pointed lobes. The flowers are produced in small cymes, the individual flowers with five red or purple sepals and five white petals. The fruit is a pair of winged samaras, each samara 2–3 cm (3⁄4–1+1⁄4 in) long with a 6–8 mm (1⁄4–5⁄16 in) seed. The seeds of Acer palmatum and similar species require stratification in order to germinate.
Even in nature, Acer palmatum displays considerable genetic variation, with seedlings from the same parent tree typically showing differences in such traits as leaf size, shape, and color. The overall form of the tree can vary from upright to weeping.
In their natural habitat, they grow in the understory; most cultivars prefer part shade, especially in hotter climates, but they will also grow in heavy shade. Some cultivars will tolerate full sun, more so at higher latitudes and less at lower latitudes; red, purple-red, black-red, bronze, and some dark green cultivars are generally more full sun tolerant. Variegated white, cream, yellow, yellow-orange, or light green cultivars mostly require shade protection. Almost all are adaptable and blend well with companion plants. The trees are particularly suitable for borders and ornamental paths because the root systems are compact and not invasive. Many varieties of Acer palmatum are successfully grown in containers. Trees are prone to die during periods of drought and prefer consistent water conditions; more established trees are less prone to drought. Moderate to well-drained soil is essential as they will not survive in poorly drained waterlogged soil. Trees do not require heavy fertilization and should only be very lightly fertilized.
Japanese maples are best to grow in hardiness zones 5–8.
II. How to Grow and Care
Sunlight
Grow Japanese maple in filtered sun to part shade. It is a suitable tree for full shade if needed, especially in the warmer zones, but different cultivars have different needs, so do some research before getting one. Afternoon sun is rarely tolerated by any cultivar, often resulting in sunburnt Japanese maple leaves.
Temperature and Humidity
Red-leaf varieties are more prone to leaf scorch than green varieties, so in hot, dry climates, green-leaf varieties of Japanese maples are usually the better choice. The trees can usually withstand moderate humidity. Generally, Japanese maples do best in USDA zones 6 to 8 though some varieties thrive in zone 5. Protect your Japanese maple from areas that experience strong winds. Young trees will also need some winter protection in the first few years.
Watering
Although Japanese maples prefer well-draining soil, they also like to receive regular water. The easiest way to regulate the soil’s moisture level surrounding a Japanese maple is to mulch it. Until your tree is well-established, take the time to water it whenever the soil feels dry, particularly when it hasn’t been raining much.
A newly planted tree needs water every 2 to 3 days for the first month. After that, it needs water at least once a week, especially without rain or snow.
Some anecdotal information suggests that cutting back water in late summer intensifies fall color. However, no scientific studies back the theory.
Soil
Japanese maple trees like moist, well-drained soil and compost-enriched soil. Loamy and sandy soil will work well, but avoid soil with high alkalinity; Japanese maples thrive in slightly acidic soil. Japanese maple trees can also grow in poor soil, but growth will be slower, and it can lead to the tree getting stressed out.
Fertilizing
Hold off on fertilizing a newly planted Japanese maple and only feed it in the late winter or early spring of the second year. Instead, plant it with compost-enriched soil. Trees with healthy foliage planted in rich soil with plenty of organic matter do not need annual fertilization.
If you need to fertilize, do this in the spring. Apply a slow-release granular shrub and tree fertilizer and mix it at half the recommended rate for landscape trees. Do not apply liquid fertilizer, as it can burn the roots. Spread the fertilizer evenly around the tree, starting at least 1 foot away from the trunk and beyond the tree’s drip line. As a rule of thumb, for every 5 feet in height, spread the fertilizer 1 foot beyond the drip line.
Planting Instructions
When planting a Japanese maple tree, consider the time of year, sunlight, soil condition, and wind exposure.
- When to Plant
Spring and fall are the best planting times for Japanese maple trees. Spring might be slightly more advantageous, allowing the tree more time to develop roots before winter. Fall is trickier since the tree is most fragile in the first few years, especially around bitter winds or frigid temperatures. It will need winter protection in its first few years if you live in a freezing zone. If you get a tree for planting in summer or winter, do not plant it. Keep it contained with moist (not soggy) soil until fall or spring.
- Where to Plant
A Japanese maple tree needs a spot where it will get dappled light or at least morning sun with afternoon shade. It will need protection from strong winds, such as the north or east side of a house or building, where it will only get morning sun. Intense sun can cause leaf scorch, which looks like a brown rim around the margins of the leaf. Its soil should be well-draining, acidic, and compost-enriched.
- How to Plant
Once you’ve found the perfect spot, dig a hole three times the width of the root ball. Set the root ball in the center of the hole, slightly above the soil line. Backfill what’s left of the hole with the same soil. Water it thoroughly.
- Container Planting
Japanese maple trees make good bonsai specimens because they will “self-stunt” or stop growing taller and wider once their roots have nowhere to go. If you plan on keeping your Japanese maple in a container, it’s best to get a small or dwarf form. A larger variety might be more likely to get stressed if confined indefinitely. Trees with higher stress levels are more vulnerable to disease or insect infestations.
Pruning
If space is not a constraint, no pruning is necessary except to remove any dead branches. Trees naturally self-prune foliage that doesn’t receive enough light, such as internal branches which are overly shaded by its own canopy. Some growers prefer to shape their trees artistically or to thin out interior branches to better expose the graceful main branches. The form of the tree, especially without leaves in winter, can be of great interest and can be pruned to highlight this feature. Trees heal readily after pruning without needing aftercare. This species should not be pruned like a hedge, but instead methodically shaped by carefully choosing individual branches to remove. They can also be pruned just to maintain a smaller size to suit a particular location. Acer palmatum can also be used as espalier.
Propagation
You can propagate a Japanese maple with softwood cuttings taken in the summer:
- Using sharp shears, cut a 6- to 8-inch section of new growth that is hardened but still young enough to be pliable, not yet mature, and woody. Only keep the top sets of leaves and remove the rest.
- Insert the cut end in a 4-inch pot filled with potting mix. For increased success with rooting, dip the cut end in rooting hormone.
- Moisten with water, but don’t oversaturate the soil.
- Place the cutting in a location that gets bright, indirect light. Mist it twice a day. Roots should develop within three to four weeks.
- Another, more involved method of propagating a Japanese maple is by grafting. It involves joining the rootstock of a closely related species with the scion or upper stock of the cultivar.
Grafting is usually done in the winter:
- Start with a two-year seedling that you previously started. The trunk must be at least 1/8-inch in diameter. You’ll need a sharp grafting knife.
- Pull the base plant out of dormancy for about a month by putting it in a warmer location.
- Cut a splice graft in a long diagonal about an inch long. Take a cutting of the same diameter from the cultivar plant, intending to fit the two together.
- Wrap the union with rubber grafting tape and secure the graft with grafting wax.
- Place the grafted plant in a place that gets sun but is not too direct. Consider giving shade to prevent scorching the graft.
- Recheck the wax in three to five days. You want to maintain a good seal and keep humidity high.
- Prune off any growth coming from the rootstock.
- Watch for new growth from the scion; that’s a sign that the graft is successful.
- Remove the wrapping once the scion develops leaves, preventing girdling.
- Plant in the ground after a year of successful growth in the container.
Potting and Repotting
Aside from their use in bonsai, dwarf Japanese maples can also be grown as container trees and moved about the yard throughout the season. Plant them in a container with adequate drainage holes since Japanese maples do not do well in soggy soil. Choose a well-draining high-quality potting soil. A terra-cotta pot works well as it wicks away extra moisture.
Repot once roots reach the sides and bottom of the pot or grow out of the drainage holes.
Overwintering
Mulching will help protect the tree’s shallow roots. Japanese maples are hardy to USDA zone 5, but container plants need protection during the winter. Move the container to an outdoor location shielded from strong damaging winds.
To protect the roots against the cold (in a container, they are much less insulated than in garden soil), wrap the container in burlap and bubble wrap or protect it with an insulating silo. You can plant stakes around a newly planted or young tree and wrap burlap around it to give it a semi-shelter.
If a cold snap is expected in later winter or early spring and unseasonably warm temperatures have spurred your tree to set leaves, you can cover or wrap the tree with a tarp. An unexpected hard frost can kill the leaves and potentially freeze the sap in branch structures, killing the branches. If it’s a young plant in a container, bring it indoors for the duration of the frigid temperatures.
Mulch Cover
Since the Japanese maple tree roots are shallow, they benefit from a 3 to 6-inch layer of mulch covering the tree’s base—spreading out a radius of about 6 inches. Start the mulch a few inches away from the tree trunk. New plantings especially need mulch to help keep the soil moist and insulate roots in winter. Mulch every one to two years, replenishing mulch over time.
Pests and Diseases
Acer tree diseases are rarely a problem – Japanese acers are pretty easy going and you can usually leave them alone after the first year or so with no issues. However if your Acer does develop a problem, you’ll want to sort it out ASAP. Here’s our round-up of the most common problems you might encounter, and how to prevent them.
Leaf scorch
If your Acer gets too much wind or sun (especially in the afternoon) and not enough water, it can get scorched leaves – variegated varieties and those with finely cut leaves are the most vulnerable to this. You can prevent leaf scorch by planting (or positioning your pot) in a sheltered spot out of direct sunlight where the tree will get some dappled shade. Check the soil regularly – if it’s drying out too quickly and you’re having to water more than twice a week, you should move it to a more shaded spot.
Weird colours
Less than impressive autumn colours? Purple-leaved variety turning green? Your Acer may not be getting enough light. If it’s in a pot you can easily solve the problem by moving it somewhere with a better balance of light and shade (not too bright, not too dark). With trees planted in the ground this tends to be a result of too much competition for light from surrounding trees – give any taller trees a trim and you should see an improvement.
Verticillium wilt
This is a fungal disease which is spread through the soil and affects the roots of trees. If your tree is affected, you might see the leaves yellowing or suddenly wilting and the branches dying back. To prevent this, keep on top of weeds because some of them can carry the fungus without showing any symptoms. If your tree becomes infected, water it heavily and apply nitrogen-rich fertilizer. If it doesn’t recover, unfortunately it will have to be removed and destroyed. If you do have verticillium wilt in your garden, be careful not to spread it via tools or shoes. Don’t grow any more susceptible plants in the area – replace them with wilt resistant plants.
Aphids and scale insects
Tiny black, white or green aphids won’t usually do too much damage, but it’s worth checking for them regularly so they don’t get out of control. They’re sometimes found on new growth in the spring, and if not removed can result in distorted or stunted growth. They secrete a sticky substance which can encourage fungal diseases or black molds if not treated.
If you see what looks like wool or fake Halloween cobwebs on your tree, it may well be scale insects, which work in roughly the same way. The solution to both pests is removing them by hand and squashing them, or hosing them off the branches if the hosepipe ban has ended by then! You can then spray the affected areas with a solution of water and oil or soap (recipes here) which will prevent the insects clinging on and suffocating any that do.
Vine weevils
These destructive little bugs can occasionally affect Acers in pots – their grubs eat the roots and the adults eat the leaves. If you’ve got vine weevils you’ll see little c-shaped white grubs about 10mm long with brown heads amongst the soil and notches in the leaf margins, perhaps accompanied by the culprits – 9mm black beetles with a yellow mark on the wing cases. To get rid of them, check the tree regularly and remove the adults by hand or trap them with sticky barriers around the edge of the pot. You can also remove as many grubs as possible from the compost or repot your tree. The best way to prevent vine weevils in the first place is to encourage wildlife into your garden – birds, frogs, toads and hedgehogs all eat vine weevils. A layer of grit or pebbles on the top of the compost will also stop them laying eggs.
III. Uses and Benefits
- Environmental Protection Value
It has strong resistance to sulfur dioxide and smoke and dust, and can purify air.
- Garden Use
Japanese maple is a deciduous tree commonly found in gardens. It is prized for its unusual bark and brilliant yellow foliage in fall. Its branching makes it suitable as a shade tree. Japanese maple is appropriate for Japanese-style gardens. Suggested companion plants include Japanese or Cushion Spurge for color contrasts. Alternatively, grow alongside Holly or Azaleas.
