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 to 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 yatsubusa 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 dissectum 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 it’s 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 about when the leaves start crisping.