Acer palmatum ‘Japanese Maple’ are beautiful, deciduous trees that grow in a variety of different sizes, leaf colors and leaf shapes. The trees are native to Japan where they grow in the understory of forests, but are now widely grown around the world with over 1,000 cultivars. Given the right growing conditions, Japanese Maples can live to be over 100 years old.
Japanese Maples are versatile in the habitats they can be grown in. They grow well planted in the ground, in pots or even as bonsai. With over 1,000 different cultivars with varying characteristics, it would be hard to find one that doesn’t go well in your garden or patio. Different cultivars are chosen for their desirable characteristics such as leaf color, leaf shape and overall tree size which are grafted onto a traditional Acer ‘Maple’ rootstock. Japanese Maples can also be grown from stem cuttings which will be exact genetic clones of the parent plant. The characteristics of Japanese Maples grown from seed can vary considerably. Japanese Maples can grow up to 33 feet tall, but dwarf and semi-dwarf cultivars only grow between 5-25 feet tall. The leaves traditionally have a palmate shape to them meaning they resemble a hand with five lobes.
Traditionally, a Maple tree’s leaves change from green to variations of orange, red or purple in autumn before they shed their leaves for winter. The leaf color of different Japanese Maple cultivars can vary between green or red, with some cultivars keeping a red pigment all year.
Common Japanese Maple cultivars:
Depending on the region, Japanese Maples can grow anywhere from full sun to partial shade, but do best when grown in full morning sun with afternoon shade. When grown in hotter climates where the soil dries out faster, they should receive less sunlight to prevent dried, scorched leaves. However, cultivars with a red pigment to their leaves can handle more sun than those with green leaves as the red pigment acts as a protectant. Japanese Maples grown in shady environments tend to develop greener leaves as they develop more chlorophyll to make up for a lack of sunlight.
Japanese Maples like their soils to stay consistently moist, especially during the hot summer months. They are very prone to losing their leaves during periods of drought or excess soil moisture. It is best to keep the soil moisture level consistent throughout the year and avoid drastic moisture level changes to reduce stress to the tree. If growing your Japanese Maple in a pot, ensure there is sufficient drainage to reduce the chances of over watering from moisture buildup.
Japanese Maples prefer well draining soil with a slightly acidic pH between 5.5 and 6.8. Soils that are alkaline with a pH above 7.0 will prevent the tree’s roots from being able to take up nutrients from the soil, leaving them malnourished. A soil pH meter or pH test kit can be used to test the pH throughout the year. If your soil is alkaline a soil acidifier that contains sulfur can be mixed in. An addition of compost or manure will also help acidify the soil. If your soil is very acidic and below 5.5, mix garden lime into the soil. To protect your Japanese Maple’s soil from erosion and to conserve soil moisture, add a layer of mulch around the base of your tree.
Japanese Maples prefer a slow release fertilizer throughout the growing season of spring and summer.
If using synthetic fertilizers, ensure they are only used at the recommended dosage to avoid over fertilization. If Japanese Maple’s are given too much fertilizer, they will put out new growth quickly, but this growth will be weak. A slow release fertilizer will produce slower growth, but the growth will be much stronger and less susceptible to damage and diseases. If your Japanese Maple has been newly planted, wait until the following growing season to fertilize. For example, if you plant your tree in the fall, fertilize the following spring. If you plant in the spring, fertilize in the fall. Holding off on fertilizing for a few months will help your tree acclimate to its new environment quicker. Applying an annual application of manure or compost at the base of the treat in the spring will not only provide nutrients, but will improve your soil’s structure if it is naturally clay-like or sandy.
Transplanting your Japanese Maple into the ground or a pot is best done in the early fall. Planting in the early fall will give your tree a chance to build a strong root system over the fall and winter months so that it can put its energy more towards top growth in the spring.
Before planting, ensure you have loosened up the tree’s root ball and removed any synthetic root wrapping.
This will allow for better moisture penetration and will give your tree the best chances at long term survival. Plant your tree into a hole twice the size of the root ball so the roots have a chance to spread out and backfill the hole with a mixture of the native soil and manure or compost. Keep the top of the root ball just below the soil surface. Planting your tree too deep will cause the roots to suffocate from a lack of oxygen.
Pruning & Shaping
Japanese Maples should be trained and shaped when the tree is still young and flexible. This will reduce the need to hard prune as often or make corrective pruning cuts in the future. Maintenance pruning should primarily be done to remove dead or diseased growth, to thin out inner branches for better air flow and light penetration or to remove rubbing branches. Hard, structural pruning of your Japanese Maple can be done to develop a certain shape to the tree and should be done in late fall or winter after the tree has lost its leaves. This will help you see where you need to make pruning cuts more easily and will give the tree a chance to put out new growth by the following spring. Light pruning is best done in the summer after the new growth has formed to further shape the plant’s foliage. Light pruning mostly consists of pruning back small branches for a desired shape.
Before beginning to prune, first make a plan to reduce the chances of mistakes.
Even if pruning mistakes do occur, the plant will eventually grow out and the mistakes can be corrected in future seasons.
Step 1: Disinfect all pruning tools to reduce the chances of diseases.
Step 2: Remove dead, damaged or diseased branches.
Stems that are severely diseased or dead will prevent further spread of unhealthy conditions such as fungal spores and homes for insects.
Step 3: Remove rubbing or crossing branches.
Crossing stems can rub against other stems, creating wounds that are susceptible to disease and insect infestations.
Step 4: Remove inward growing branches.
Removing inward growing stems opens up the canopy for better air flow and light penetration
Step 5: Remove downward pointing branches.
This growth can get shaded out or will rub against other branches.
Step 6: Prune back weak branches to the next healthiest node/leaf set.
To influence the direction of a shoot to grow outwards.
Step 7: Prune off suckers.
These grow from the base of the plant at the root stock and grow more frequently with more pruning as a stress response. Allowing these suckers to grow into maturity will cause your Japanese Maple to revert back to an original Maple tree which is the rootstock that Japanese Maples are grafted onto.
Japanese Maples are hardy trees with few major disease problems, but they are not completely immune to diseases. The most common diseases that afflict Japanese Maples are Anthracnose fungal disease which mostly grows on the foliage and Verticillium wilt which is a serious fungal disease that lives in the soil and attacks plant roots.
Anthracnose fungal infection symptoms are brown or black lesions on the leaves and buds. This fungal disease is most common during the warm, humid seasons of spring and fall. Anthracnose can be treated with a copper fungicide sprayed directly on the affected parts of the tree.
Verticillium wilt symptoms are wilting and curling of the leaves and stems, dry leaves, and discolored or complete die off of branches. There is no cure for this disease, but it can be controlled by pruning off affected parts of the plant and keeping the tree healthy by regularly watering and fertilizing.
If you have any questions about how to grow Japanese Maples, we will be happy to assist you in a virtual telehealth appointment with one of our Plant Specialists. Please click on one of the options below to book an appointment.