Most JM's will do well in a pot for quite a while, but for a 4' tree in a 3 gallon, I'd repot it, as it may well be rootbound. JM's really don't like to freeze, so once it drops its leaves it would probably be best to put in the garage. Over the winter, I'd keep it moist, but not wet. I'm from the PNW, where it rains for 7-9 months out of the year in the fall-spring, so they don't mind being wet, as long as the soil they're in drain well.

Agree with all of the above - you need to keep the tree cold during its dormant period but don't allow it to freeze. The garage is a good bet.

To see pics of a mature, Google "Acer japonicum 'Aconitifolium'", which is the correct botanical name for this tree. Also called fernleaf fullmoon maple :-) Gorgeous in its fall color!

Quite often, when you get a Japanese Maple, it will have recently been bumped to a larger size can, so there is no real urgency to do an out of season repot in the immediate. At most, you should pot up after cutting some shallow slits in the outside of the root mass. Repotting should wait until spring, and be undertaken just as you see buds start to move in anticipation of the spring flush.

Once a plant has become root-bound to the point that the root/soil mass can be lifted from the pot intact (at any point in its development), the plant will be permanently and negatively affected because of the problem roots that develop from the congestion (entangled, crossing, constricting, girdling, j-hooked .....) so you should be sure you correct those problems during your repotting sessions. Potting up won't correct those problems, even if you do see what some might consider a growth spurt after potting up. In reality, if you do see a 'growth spurt' after potting up. it's actually evidence that the plant has been growing under limiting conditions. Potting up only partially alleviates the limiting congestion, allowing the plant to grow a little closer to its genetic potential. Repotting, and its accompanying root work, restores the potential the habit of potting up robs.

Your choice of soil (when you repot) will probably be one of the most important decisions affecting the trees growth/vitality that you'll make.

Al

Thanks for your advice everyone, I really appreciate it! The tree is not root bound at this point. I think I will wait until next spring to repot it.

Right now I have been keeping it in a shady spot. I eventually want to plant it in the ground. Can Aconitifolium take much sun? I live in northern Utah and currently have a Bloodgood planted in full sun with southern exposure and an Oshio Beni planted in partial sun with eastern exposure. Both of these trees have been planted for many years and are doing great and do not burn.

Thanks
Linda

It needs dappled shade to look its best, especially while in a container.

Al

Most trees and shrubs at outlets here are under-potted, in fact there is a tendency for ones in adequately large pots to not sell, ironically, because the bigger pot makes the top look small. When the wind comes up during the summer sales yards are often soon strewn with toppled trees in under-sized pots that do not have enough weight to support the top - this being worsened by the fact that these are often not getting the more frequent watering they need.

The main issues with outdoor container growing are keeping the roots cool and moist in summer, unfrozen in winter, and the heavily watered, often soil-less potting medium adequately fertilized. You also have to address the recurring problems of the roots soon filling the pot and the potting medium decomposing, needing to be replaced. You either move the plant into a bigger pot or tub ~every year or you have to shave the outside of the roots, replace the soil that comes away when that is done, in order to re-use the same container for some years. This is liable to have a dwarfing effect on the top, as does the annual cutting back of the roots of bonsai - which is done specifically to produce that outcome.

Most plants at nurseries are OVER-potted AND root bound. Root bound because of the economics of bringing a plant to market (repotting labor isn't cheap) and over-potted because bumping a plant a can size means instant profit - you get more for a 3 gallon plant than a 1-2 gallon, even though it might easily be the same plant.

Shaving roots off the outside of a root mass and potting up instead of repotting ensures the plant will suffer the limiting effects of tight roots in the remaining root mass. The limitations will affect the plant permanently - or until the congestion is remedied via repotting/root pruning. It's a poor substitute for repotting, which includes bare-rooting in either 1 or 2 repotting sessions at least a year apart, correcting root issues, removing large essentially useless roots, and replacing the old soil. The object is to maximize the number of fine roots and minimize coarse rootage.

Bonsai are repotted religiously, and roots pruned dramatically. It doesn't have a dwarfing effect on the trees. In fact, quite the opposite is true. A freshly repotted plant will have longer internodes, larger leaves (coarser growth) than a plant in need of repotting. There are a number of ways bonsai growers induce dwarfing (smaller leaves - more leaves, shorter internodes), but none are related to root removal.

Al