Japanese Maple FAQ

A Japanese Maple is really any maple that is native to Japan.  As well as what we commonly call “Japanese Maples”, there are quite a few other beautiful species:  “Snakebark” maples, “Trident” maples and large trees like the “Painted Maple.”

But when we talk about Japanese Maples in horticulture and gardens, we usually mean only a few species.  These are Acer palmatum and Acer amoenum – which are sometimes grouped together – Acer japonicum and Acer shirasawanum.  By and large these species cross-breed freely (hybridize) which has led to many garden varieties.

It’s amazing to think, but these four species alone are so variable in size, color, leaf shape, bark and autumn color that they account for thousands upon thousands of named Japanese Maple selections available on the market!

In some places, the Japanese Maples belonging to our four species, and their crosses, are called simply “Acers”.  In truth an Acer is any member of the maple family, which has over 150 species.  But when going to buy a plant for your garden, if someone offers you an Acer, chances are they mean a Japanese Maple.

Because of the vast varieties of Japanese Maples – dwarfs, uprights, reds, greens, laceleafs, variegated and more – and the difficulty of knowing for certain to which species they belong, the Maple Society has adopted a simple classification aimed at helping the consumer know what they’re going home with.  Find out more about the Official Classification of The Maple Society.

Emery D., Normandie, France

When you shop in a nursery or garden center, you’ll notice that the Japanese Maples often have specific names.  Some of these are descriptive, (like ‘Rhode Island Red’), some are Japanese, (‘Sango kaku’), and some seem to make no sense at all!  These names are how we describe cultivars.  Broadly speaking, a cultivar is a selection of a plant that has some desirable features, like great autumn color, interesting leaves or bark.  The person who discovered it decides the name, and starting from that point all new plants are made by forms of cloning.  That means that every ‘Uncle Ghost’ is genetically identical to the first one.  Nursery people show this by using single quotes around cultivar names.

Most Japanese Maple cultivars are produced by grafting, which is a cost effective way to make strong plants that are identical to the original in every way, even if the original selection – and quite a few Japanese selections were made hundreds of years ago – is long gone.  Other cultivar reproduction methods include rooting and air-layering, favored by Bonsai artists.

Japanese Maples grown from seed are not cultivars, even if the parent plant is a cultivar.  These maples are called by their species name (like Acer palmatum) or sometimes one of the “common names”, like “Mountain Maple.”

One reason we have so many excellent cultivars is because Japanese Maples vary so much between generations.  That’s also a reason why growing seedlings is so much fun: you never know what will happen, and maybe you can name a selection too!

Emery D., Normandie, France

Differences between trees in ground, pots. Wind.  Differences between interior continental and coastal sun.

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A well-pruned maple is a thing of elegant beauty, a statement to wow your friends and neighbours, and often the most photographed tree in the garden.  When needed good pruning creates a structurally sound tree, with healthy, balanced growth, that is better able to deal with environmental stresses such as extreme weather or pest and disease attack.

When to prune?

Summer is a good time to prune your Japanese Maple as it is full of energy from photosynthesis, meaning that will easily heal any cuts.  In summer, look to prune while the maple is not enthusiastically growing: between the spring and summer growth periods.  Try to avoid pruning in spring as the sap is rising from the roots to the tips of the branches and cuts can bleed profusely, which is stressful for the tree and possibly you too!  In order to reduce the chance of fungal issues, which thrive in damp conditions, carry out pruning on a dry day.  Mid-winter is a better time to make large pruning cuts, as doing so in summer will remove a lot of foliage which can lead to a large loss of energy for the tree.

There are occasions when you may have to prune at a time that is not ideal and this could be due to an unavoidable incident, for example a storm that has damaged a branch and left an untidy wound.  In this case, it is probably best to prune to create as clean and neat a wound as possible to give the tree its best chance of healing.  Avoid pruning any trees that are under environmental stress, such as drought.  If a tree is not in full health with plenty of reserves, pruning can often make things worse as it may then be faced with having to heal new wounds with depleted resources.  Once an ailing tree’s health has been restored via good husbandry, then pruning can take place.  The exception to this rule is when diseased or damaged wood must be removed.

FIGURE 1:  Clean, sharp tools are of the utmost importance

Which tools to use?

A good quality pair of bypass secateurs and a pruning saw (FIGURE 1) are all you really need when pruning but the most important thing is that they are clean and sharp.  A cut made by a sharp edge will heal much more readily and with less scarring than one carried out with blunt blades which can tear the plant tissue and leave jagged edges.  Equally, cleanliness is vital to stop the spread of disease between branches and trees and the simple wiping of blades with surgical spirit or rubbing alcohol will work wonders.

For larger cuts use a pruning saw, ideally one which cuts on the pull stroke, as this will make an excellent cut that will heal well.  Don’t use loppers to prune as they are much clumsier than secateurs and can easily damage the thin bark.

 

How to prune?

Firstly, identify any damaged, diseased or dead wood, all of which should be removed.

Approach with a clear idea of what you would like your Japanese maple to look like once pruned, then trim a little, stand back to look, trim a little more and so on until you’ve achieved the desired result.  Aim for a well-shaped tree with an open habit that allows plenty of light and air into the canopy; this not only looks pleasing but keeps the tree in the best possible health.

FIGURE 2:  Pruning in front of a pair of buds allows successful compartmentalisation

All maples have opposite leaves, and each pair of opposite buds on a stem is (almost always) set at 90 degrees to the next and previous pair.  In other words, when one pair of buds is in the same plane as the ground, the next pair will be perpendicular to the ground.  This allows you create that wonderful ‘layered’ look with your Japanese maple.  To achieve this, always prune to just in front of a pair of buds that are in the same plane as the ground i.e., horizontal.

When pruning anything as thick as a pencil or less, try to make the cut around a centimetre in front of the buds (FIGURE 2).  This will allow the wound to be successfully compartmentalised or ‘walled off’ to ensure die back doesn’t occur down the stem.  A wound will always heal better if there is a consistent flow of sap nearby and so it is ideal if there is a bud on either side of a newly made cut.  In the image (FIGURE 3), you can see that dieback occurs on the side without a bud.

FIGURE 3:  Reduced sap flow on the underside has resulted in dieback

When using a pruning saw, first make a cut higher up the branch to remove some of the weight and avoid the risk of tearing the bark.  The final cut should be as close to the branch collar as possible to ensure the best healing (FIGURE 4); ‘flush’ cuts are be damaging and can allow the entry of disease into the main trunk which the tree may struggle to recover from.  Conversely, leaving too much of a stub means the tree cannot heal the wound successfully and this can lead to the chance of rot setting in.  Cutting at the branch collar lets the tree heal as quickly and naturally as possible.  Don’t use cut paste or sealant, just leave the area open to dry and heal naturally.

FIGURE 4:  Successful occlusion has resulted in a well-healed wound

The best way to avoid making large cuts is formative pruning, carried out when your tree is young.  This minimizes injury and maintains its future aesthetic.  You need to visualise the growth habit of the tree some years into the future: creating a young tree with a good structure and imagining how certain young stems will grow and mature is the very best way to ensure a happy, healthy tree with a beautiful structure.

A well-pruned tree should look like it has never been pruned at all.

 

Miles H., Sussex, UK

 

Root bound and what to do next… or how to attend to containerized maples in order to keep their health and develop a strong root system.  Root pruning is also a great way to keep trees at the size you want, without outgrowing the container.

Here’s a step by step approach so you can easily follow what to do.  I had the same dilemma last year with the cultivar ‘Kogane nishiki’.  Once you decide to take on the project, you can leave it until the spring of the following year. The work pictured here took place in the beginning of March, 2020.

When I decided the job needed doing it was very wet and cold, and I thought we could be in for a bad winter. It’s better to wait and err on the side of caution: when your tree is asleep it will be fine in the old pot.

The first picture is the tree from the fall of 2019, after it had been in its container for a few years, with the intention of planting it out exactly where it is

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In the second, taken beginning of March 2020 you can clearly see that the root ball needs attention.

 

The next shows the removal of all girdling side roots and very thick crusty base, trimmed off with a saw then the remaining visible little side top and base roots were then teased out slightly to encourage their new growth after planting.

 

The next picture shows you its new planting hole and the very shaley ground I’m blessed with! I also add some new growing medium with the addition of mycorrhizal granules to help with the new root system.

Next is the tree in it’s new spot. It basically took an hour from start to re planting, so not a hard job by any means.

This tree really progressed this year in good growth and colours, and will be left until the summer of 2021 then will be lightly branch pruned to create a more aesthetic form.
Mark B., Yorkshire, UK

“What kind of soil do pot your maples in?” is one of the most common questions Japanese Maple fans ask each other, because everyone has struggled with it.  (Except that person we all know, who insists they just jam maples into pots with the perfect garden soil they’re blessed with!)

Container soil, sometimes called substrate, is as individual as the gardeners talking about it.  What’s more, depending on local climate (temperatures, humidity, sun and wind exposure) and watering frequency, a recipe that works well for one location may not work for another.

The fundamental issues are drainage and water retention.  The first thing to know is that “Japanese Maples hate wet feet.” They will never thrive in a substrate that stays wet all the time, or becomes filled with stagnant water.  Most people experiment to find a balance between drainage and water retention that’s right for their climate.  If you live in a hot climate, or your potted maples are exposed to sun or wind, you need a substrate that holds enough water to get them through the day without drying out completely.  So in the Central Valley, California, you want a substrate that holds more water than if you live in a cool and wet climate like southern England or western France.

For most, the key ingredient is pine bark, either composted or partially composted, and in chunk form.  Add to this a mineral component, like small grade pozzolan or river gravel, and expanded perlite.  The mineral addition adds uneven surfaces in the substrate that help keep it oxygenated and uncompressed; and also considerable weight to the pots, a real advantage if they’re in a place where they tend to blow over.

Clockwise from top left: expanded perlite, pozzolan, river gravel, partially composted pine bark, pine bark

In the cool, rainy climate of Normandie in France, the substrate needs maximum drainage and limited water retention. We achieve this with a formula of approximately 40% pozzolan, 30% composted pine bark, 20% pine bark chunks and 10% expanded perlite. We don’t sweat the details and measure or weigh; we just do it by eye until it feels right. If you take the resulting substrate and squeeze a handful together, it should immediately fall apart and not seem at all claggy or sticky. This is “maximum drainage” substrate. The nutrients mostly come from osmocote slow-release fertilizer applied in spring.

 

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Free draining substrate in a 12 liter pot

Others add some multi-purpose compost to their mix, like the famous John Innes no2 and no3 found in the UK, though it’s worth remembering that these may vary widely by brand. Another recipe for somewhat quick draining, but more water retentive, substrate is 60% peat or coir, 30% small caliber pine bark chunks, 10% multi-purpose compost. Yet another very successful container gardener simply uses 50/50 compost/composted pine bark.
The hotter your climate, the more compost you’ll want to add. Experimentation is the only way to find the right balance for your location.
Contrary to the popular myth, still spread by many non-specialist nurseries, Japanese Maples don’t need acid (or ericaceous) soil. They do best in slightly acidic to neutral soil.
One last thing worth mentioning: the substrate from the nursery, when you buy your maple, is often mostly peat or coir and stays very wet to support hot greenhouse conditions. In almost all conditions this wet compost will cause problems for maples at home.
Emery D., Normandie, France

 

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Many people wonder which is the ideal environment for their Japanese Maple: in a pot, or in the ground?  Here’s a “pros and cons” approach to the question.

Potted PROS:

• Can be moved around to suit the space you have.
• Can be moved into shade when needed.
• Correct soil can be used.
• Can control size.
• Suitable for smaller spaces.

Potted CONS:

• Can blow over, causing damage.
• Roots are vulnerable to freezing or overheating.
• Must be repotted every 2-3 years.
• Drys out quickly, so regular watering required.
• Needs taking care of if you go on holiday.
• Needs yearly feeding in Spring.

Ground PROS:

• Can take up nutrients already in soil. (no feeding).
• Requires less watering than pots.
• Can go grow to their full potential.
• More stability, less likely to blow over.
• Less time consuming. (No holiday worries).

Ground CONS:

• Cannot be moved into shade.
• May grow large if left alone, a problem in small gardens.
• Not all soils are equally suitable, e.g. clay can be difficult.

You can see that there are more pros for growing in the ground, but only slightly, so pots or the ground is suitable for your Japanese maple. These points are something to consider when making a purchase, and of course choosing the correct maple for the position in your garden: i.e. dwarf, mounded or upright, sun or partial shade.

There’s room for one maple in every garden, but planning on which tree you have is so very important and the impulsive purchase will more than often lead to problems.

Derek (aka Acerholic), Hampshire, England

Article should stress moving up gradually in pot size (stagnant water issues), don’t impede water flow by putting shards or gravel in the bottom of the pots, unimpeded drainage holes.

 

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I have found growing japanese maple from seed to be a simple and rewarding process. There are a lot of techniques: I have been most successful in growing Japanese Maples from seed using the refrigerator method. I collect my seeds from the last week of September through December, when they are fully brown or dry. Here are step-by-step instructions for growing Japanese Maples from seed using the fridge method.

1st Step. Collect your seeds. I sometimes soak my seeds the same day they are collected. Seeds that are not soaked on the day of collection are stored in a cool dry place. 

2nd Step. Soak your seeds. Soak the seeds for 24 to 48 hours in hot tap water. I use a jar because I collect hundreds of seeds at once. Within this 48 hour period, most of the seeds will sink to the bottom of the jar. I remove these and soak the seeds that are still floating after this initial 48 hour period for another 24 hours in new hot tap water.

3rd Step. Drain and collect the seeds that have sunk to the bottom. I use a colander to drain and rinse my seeds off .

4th Step. Place the rinsed seeds in a ziplock bag or jar in the fridge until they start to sprout (typically 60-120 days, sometimes more). Check the seeds weekly. Sometimes the seeds can mildew or grow fungus. If this happens, take the seeds out, rinse them and the bag off very well, and then place them back in the fridge.
Some people like to use a mixture of sand and peat during the cold period, with couple of drops of copper fungicide. But this is how I do it.

You’ll notice later that the seeds start to germinate.

You can either place them in individual cell seed trays or spread them over a cell tray with drainage holes. Cover seeds slightly with the growing medium and water them.

The tray with the cells makes it easy to slip pot/transfer into the next size growing pot.

With the solid seeds tray, the seedlings should be repotted doing late winter to early spring into their new growing pots.

Growing medium (soil or substrate) is very important. I have found pine bark mulch mixed with perlite to work best for me.  Whatever you use, make sure it is a free draining mix the doesn’t hold a lot of moisture. A mix that holds too much moisture can keep the root too wet, causing root rot.

Derek B., RI, USA

The Maple Society does not recommend use of chemical insect control or other phytosanitary measures.  Copper (Bordeaux Mix) pulverization (not paste or paint) is standard treatment for bacterial or fungal issues.

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In most climates maples in ground don’t need watering after being established except in cases of severe drought. So, mostly about pots, symptoms of over-, under-watering, drainage (see substrate), letting dry out.

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Don’t plant too deep, see the root flare.  Check for circling roots.  Don’t amend unless you’re on real clay.  Mound planting in wet areas.   Mycorrhizae.  Don’t stake when you don’t need to.

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Alain K. will hopefully provide this article.  Otherwise someone else will have to do it.

 

 

 

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