Japanese Maple – Complete GuideJapanese Maple – Complete Guide
Japanese maple is one of the most desirable and versatile plants available to the gardener and with such a comprehensive range of colors, leaf types, shapes and sizes, one can be found to fit in with any planting scheme. All are adaptable to a wide range of conditions and the perfect site is not a prerequisite for growing a Japanese maple successfully.
For a color-coded garden the choice is vast; from cream and the palest green imaginable through every conceivable shade (with the exception of blue!) to reds that appear almost black. And that’s just the spring color. In the autumn they provide a display of color that can’t be rivaled by any other group of plants.
Leaves range from dissected forms that look so delicate you would expect them to blow away in the slightest breeze, but in reality are amazingly tough, all the way to large, palmate shapes. Some dwarf forms have left no more than half an inch across whilst others can be up to six inches.
With such a wide range of cultivars to choose from, the need for a narrowly upright form, a wide-spreading form, a miniature shrub or a cascading or weeping form can be found to match your exact requirements. In terms of size, there are cultivars that are suitable for a window box all the way up to a garden of several acres and most are happy to grow in any shape or size of the container.
Because of their compact and non-invasive root system, they will happily blend in with other plants, be it a mixed border, rockery or large expanse of lawn and it goes without saying that they make perfect accent plants. Soil types are not a limiting factor and even the most apparently hostile soil will support them.
Should a Japanese maple be grown in shade?
Should a Japanese maple be grown in shade requires a very short answer – no. There are a number of reasons why it’s not advisable to shade them; first and foremost it’s unnatural. Most people think of a Japanese maple as being a shade tree but in reality, the only trees that are shading a Japanese maple are other Japanese maples.
In the wild, Acer palmatum will get up to sixty feet and in cultivation, they will reach, in time, a similar size also. The illustrations on this page are of Japanese maples growing along the upper Tomoe river by the Taijutsu Bridge in Aichi Prefecture in Japan. There is a distinct delineation between the maples and the conifers along the river bank – the former are growing where they can get the maximum amount of sun. And these are not small trees either; the people in the photos provide a sense of perspective.
The path from the river to the Kohjakuji temple threads through more maples and gives a better idea of how large these trees really are, whilst the first picture shows the nearby Mount Iimori – the maples are growing amongst the conifers and not underneath.
The other reason Japanese maples should not be shaded is because of the need for the sun to fully develop the leaf color. When grown in shade, or even dappled shade, what should last several months or be particularly intense, will fade very quickly or not develop the full depth of color that a particular cultivar is renowned for.
The argument that Japanese maples burn in full sun is nonsense and has nothing to do with the intensity of the sun but rather the quality of the root system. Commercial nurseries in New South Wales; Australia, the North Island of New Zealand and South Africa all grow Japanese maples out of doors with no shade cover without any ill effects – it would not make financial sense to grow them this way if they were continually getting scorched. In mainland USA the only place where Japanese maples are likely to encounter problems in southern Florida and that’s down to problems in the winter rather than what happens in summer.
If your garden only has space with dappled shade or sun part of the day, they are still going to grow but they are going to be slower plants with less developed color compared to a maple grown in full sun. The key, as I mentioned earlier, is the quality of the root system – easily achievable with plants in the ground but slightly more problematic with plants in containers.
Container growing in a hot summer climate can present something of a challenge if we’re looking for perfection but there are a number of techniques that can be utilized and I shall be looking at the options in detail in future posts.
A suitable Japanese maple for growing in a pot
A suitable Japanese maple for growing in a pot was a thought that occurred to me at a recent flower show I was exhibiting at. I was asked if I sold Acer palmatum Osakazuki and when I inquired if she had a large garden was told that is was for growing in a pot! It transpired that she wanted the autumn colors and didn’t know that it could get to thirty feet tall or more. We eventually decided on Acer palmatum Kamagata, with brilliant red autumn color and dwarf enough to spend many years in a container. Although there are many cultivars that are ideally suited to pot-growing, there are many more that are totally unsuitable after only a few years and pruning to keep them under control only encourages them to grow larger.
The other problem, of course, is the need for constant repotting; the alternative being the roots strangle themselves or smash the pot. And with a heavily congested root ball, the ability of the plant to obtain sufficient moisture is reduced each year. resulting in the all too familiar sight of crisp leaves as summer approaches.
Taking as an example the usual choices of Atropurpureum or Bloodgood for growing in a container, after ten years a tree of about eight or so feet tall with a trunk diameter of approximately two inches is going to need a container at least two to two and a half feet in diameter to be able to grow happily. I’m often told by visitors to my stand that they have plants of the same age but in far smaller pots and on enquiring am told that they are only two or three feet tall and never get fed. Further discussion reveals that the leaves dry out every summer but come back the following spring – an obvious sign that the plant is crying out for attention.
Once potted on into the appropriate growing medium they will effect a remarkable recovery but ultimately the larger cultivars are always going to be at their happiest when growing in the ground. As well as the three mentioned above, other popular cultivars that should be avoided are Sango Kaku, Seiryu and shirasawanum Aureum. These are only going to be happy in a container for a few years at most.
Of the cultivars that are going to make ideal container plants, the choice is huge and only limited by what is stocked by your local garden center or nursery. Any of the witches’ brooms can be used, these produce rapid growth for the first few years and then settle down to a lifetime of short, stubby shoots and would take twenty years or more to reach five feet. The Yotsuba forms such as Little Princess and Kiyohime are good choices also; these are wider than tall and form a low clump of dense foliage. Finally, the dissected forms, the majority of which are going to produce low, spreading, cascading plants and are the classic choice for a container.
Another consideration should be the aesthetics of the plant/container combination and this can be achieved quite easily when a dwarf form is chosen. If we take a cue from bonsai growers we can get an idea of what shape pot will go with a particular style of plant, bearing in mind though that the depth has to be consistent with growing a normal plant that is not going to get most of its roots chopped off each year. Look also at the pots that palmate leaved forms such as Deshojo are grown in; they are almost as wide as the plant itself.
Taking the time to select an appropriate plant will reap dividends in years to come as it will be happy to be containerized so long as you don’t forget to pot on occasionally. If you’re not sure when the plant will give you a hint when the leaves start crisping.
Potting mixes for a Japanese maple – peat-based
Potting mixes for a Japanese maple can use a wide range of materials but they must have one essential attribute – good drainage. Peat based potting mixes, of the type that’s commonly available in garden centers and DIY outlets, don’t, on their own, meet the requirement above. The problem is further compounded by their use in large containers where the plant might be in the same pot for five years or more. A multi-purpose potting mix is just that; a grade that is the best match for a very wide range of plants grown for the short term in small pots.
Whilst peat has two desirable attributes – it’s cheap and it retains moisture, the drainage potential is lacking in the sort of scenario we might to want to use it in. The main stumbling block is compaction as the weight of the water it can hold in the pot will gradually compress it and the action of regularly watering the surface helps to accelerate that compaction.
The solution is to add a skeleton, for want of a better word, that resists compaction but allows the peat to fill in the spaces and provide the water holding capacity we need. There are a number of additives we can use and their suitability is governed to a large extent by the size of the pot. Bark or wood chip, perlite, and vermiculite are the most suitable extras for improving peat and have the advantage of being a similar weight and density to peat, allowing for easy mixing and no separating out once in the pot. For that reason, gravel, stone chippings or similar should not be used as they will gradually migrate over time towards the bottom of the pot due to the disparity in density.
Vermiculite is best suited to small pots up to 8” dia. using either a medium or coarse grade, the medium being the most readily available. Perlite can also be used for small pots but because of it’s more rounded structure and better draining potential, can be used for larger pots up to 12”, particularly if the coarse grade rather than medium is used. Chipped bark, wood chips or a mixture of both, depending on the size used, are suitable for the smallest pot right up to containers of several feet in diameter. For pots up to 12” my recommendation would be to use chips graded approximately ½″ and for larger pots ½″ to 2″. For small pots, anything much below ¼″ is going to have little or no effect as we’re approaching the same size as the peat particles.
As to the types of chipped bark or wood to use, anything is suitable; from composted chipped pine bark such as that used for orchid composts (and the most expensive option) to home-produced wood chips. Sterilizing is not necessary as the fungi that will colonize the chips are concerned only with eating decomposing wood and will not affect your Japanese maple. Shredded bark or wood is not really suitable as it will not flow freely when mixing with peat and tends to form a more plate-like structure within the pot.
We now come to the question of concentration. The often seen instruction to add 10% perlite or whatever to improve drainage is a non-starter. Going back to the ‘skeleton’ analogy, for it to work the additives need to be in contact with each other or at least the majority. For that reason, anything less than 40% is not going to work effectively but for the purpose of simplicity, a 50/50 mix is ideal. The percentage additive can be increased up to 70% but it’s water holding capacity is going to reduce. That’s not a problem as watering frequency can be increased – it’s far easier to put water in than to take it out! This method will provide the ideal growing medium for your Japanese maple – perfect drainage but still with the ability to retain moisture, and overcomes the problem of creeping compaction and the side effects that cause with long term potting of Japanese maple.
Japanese Maple Questions and Answers
Further information regarding Japanese maple question no.4 has been received (re-printed below) and I’ll clarify all the points raised.
I think this was the second summer that I had the trees. I put them in these pots, using whatever dirt was in them, to begin with (I bought the apartment and the pots were on the terrace with dirt in them) – no idea what kind of soil it is. I believe the trees were close but not identical when purchased (at Home Depot). The healthy one gets more sun than the sick one – neither gets full sun. I am constantly weeding these and the other pots.
The watering system is a drip system. Both trees have 2 adjustable emitters in them, all were wide open. I had been watering them 2 x a day for 5 min. When it got hot this summer, the tree on the left (the one that’s in bad shape now) was looking like it needed more water. Also, most of the rose bushes looked like they needed more water, so I set the timing to 2 x 10min. The rose bushes had improved. The tree seemed like it was getting better, but that was short-lived and is now in the state you saw in the pictures.
I started reading online – came up with all kinds of funguses that it could have caught.
A few other notes: I use Miracle Grow – one scoop every month or so per pot. Not so scientific, and now not so sure it helps.
As soon as I got your reply, I turned the timer to 2 x 5min a day and shut one emitter (in each tree) off entirely, the other emitter I closed down to a drip (when wide open they squirt 6 little streams out). Do I need to worry about under-watering?
Today I got home early, and took a drill to the bottoms of both pots, putting a ton of holes in the bottom, and all the way around the bottom vertical side edge, and put a few holes even further up. Not an easy task – these things weigh a ton and I had to tip them and move them around. From this, I learned that there are stones in the bottom of the pots – maybe a couple of inches deep. I also learned that the dirt in the pots is dark black and pretty wet from what came out on the drill; not sure but these pots may be full of plain potting soil.
So from what you said in the web site, do I need to dig the trees out of the pots and try to get the dirt out of the roots? Won’t that hurt them? I’m not even sure I will be able to do that. If so, from what your article says, I should get a bag of peat moss, and a bag of wood chips (like when they shred a tree on the side of the road?) and mix them up, then mix that in to be about 40-50% of the soil in the pot? If I am going to try this should I do It now? Or wait till winter? I am in NYC.
My gut tells me that in the spring I will be finding out how extensive the damage to the tree is; should I cut off all the branches without buds at that time? I think a lot of it will probably live – it’s sending out new little branches with leaves on them in a bunch of spots now.
Oh – another question – why on the “healthy” tree have the leaves turned green?
Reply: The growing medium probably contains a large number of weed seeds so should be discarded and fresh potting mix used instead. As they are still in growth it’s best to wait until the leaves have dropped and they go dormant. What dirt can’t be removed by hand should be washed off so that you end up with completely bare roots.
The new growing medium of equal parts peat and chipped bark will require the addition of powdered dolomite (magnesium) limestone to neutralize the peat. Half an ounce mixed in with each gallon of peat will bring the pH up to neutral – they don’t need acid soil. Garden World in Queens (www.igardenworld.com) sells bags of Schultz peat and potting bark. You could also try Plantworks on 800 611 2270. If you can’t get straight peat, any multi-purpose potting compost will do but avoid anything with Miracle Grow on the bag! Roadside tree shreddings should be avoided as they will need composting for a couple of years before they can be used.
For feeding, a few ounces of fish, blood, and bonemeal mixed in with the growing medium will suffice, and then subsequently sprinkled on the surface once a year. Alternatively, a 12 or 24-month slow-release fertilizer can be sprinkled on the surface next spring. Again, do not under any circumstances use Miracle Grow. The two contacts above can probably advise you on suitable slow-release fertilizers.
When you repot, it’s not necessary to have any stones at the bottom of the pot; if you don’t have a free-draining growing medium a layer of stones or crocks will make no difference. It would also be helpful to mulch the surface – a sheet of plastic held down with a thin layer of stones will ensure moisture levels don’t fluctuate too much. In their present state, the likelihood of under-watering is probably non-existent as the root-ball sounds as though it is completely saturated and your revised settings will be more than adequate. The existing pots can be re-used.
As to a fungal infection – this can be discounted as the damage stems from the roots being water-logged and fungi are only going to be interested in feeding on dead and decaying wood. Any dead roots should be pruned back to healthy tissue once all the potting soil has been washed off.