Any Japanese maple can be grown in a container, provided you correctly match the size of the tree to the size of the container :-) And this means matching both the size of the tree now (as determined by rootball, not height) as well as estimated mature size (height and spread) of the tree. Be aware that container grown trees seldom grow as fast or as large as the same tree inground - the container culture has a natural dwarfing effect.

How large are the containers these trees are in now? 2, 3 gallon? For long term container growth, I would be looking at containers that have a diameter of at least 20-24 inches and a depth of 18".......larger is not a problem.

You will need to pay attention to potting soils....either making your own or finding one textural and durable enough to stand up to time. Planting is as for any other container plant or for that matter, any inground plant. The other issues to consider are fertilization (should probably wait until spring now), the ongoing need for water, protection of both the pot and the tree in winter and the frequency of repotting and root pruning down the road.

You can certainly ask additional questions on the container gardening forum although I think we can answer pretty much anything here as well :-) I would suggest you read through the long-running thread on Trees in Containers on that forum. While not specific to JM's it does discuss a whole host of other container growing issues re: trees in general and is hugely informative.

Here is a link that might be useful: Trees in Containers, part 3 (with links to 1 & 2)

Thanks gardengal48, for your helpful and thoughtful response. I suppose I should post these questions in the Container Gardening forum; I'd like to post them here also but I'm thinking that might be a big no-no. :0)
But I do have questions regarding planting some additional Japanese maples in the ground. Thanks to you and others in this forum, I have a general idea about this but, with your indulgence, I'd like to review them in the event I've erred.
First, dig the planting hole at least twice the diameter of the container and no deeper than the container (possibly not as deep to prevent the plant from settling below the soil line); do not amend the native soil (unless it's hard clay or pure sand; tease out the feeder roots carefully, allowing them to radiate out from the rootball, but keep the rootball intact as much as possible; backfill with the original soil; mulch.
Now the questions. Is there any situation in which I should wash away the original soil medium from the roots before planting in the ground? What should be done with roots encircling the rootball (rootbound)? Between now and spring, what watering regimen do you suggest? Can you rootprune the plant at a later time? If so, why and when is it advisable?
I've asked more questions than is courteous. But, as my three-year-old grandaughter would say, "Take pity on my poor old paw-paw". :0)
Have a wonderful day.
gary

Any questions about maples - Japanese or not, grown inground or in containers - can be asked here. Many regular participants on this forum grow JM's in containers, myself included, and have a lot of experience and knowledge to share.

Japanese maples have quite delicate root systems that resent a lot of disturbance. While I would not hesitate to correct girdling roots or gently tease out the rootball, I would hesitate to wash or completely bare root the tree unless it was fully dormant. And even then I would want to be assured there was no significant root activity still going on.

Are these inground trees or containerized? If inground, watering is not really an issue, as winter rains/snows are more than sufficient. Containerized plants will also need moisture - not too much but you do not want to let them dry out completely. Take advantage of rainfall or if undercover, check soil periodically and water as appropriate.

Root pruning is primarily applicable only to long term containerized trees and it is a common method both to rejuvenate potbound plants and to maintain a containerable size. How often one needs to do so depends on the size of the container and the tree in question but with most JM's, maybe every five years or so? And you want to replenish/refresh the potting soil at this time as well. Again, as you are messing with the root system, you want to do this when the tree is fully dormant.

gardengal48_ Am much obliged for your suggestions. Knowing these maples can't survive with wet feet, I really want to guard against overwatering. With temps beginning to drop here in Virginia, I've pretty much stopped watering my deciduous shrubs, hostas, etc. With regard to only those planted in the ground, I'm assuming the same applies to Japanese maples: water when planting but, between now and the first frost, water a bit only if there is some leaf scorch or the tree looks stressed. Sound about right?

Oops.
Last fall I took a bunch of root bound container maples and pruned the heck out of their root system. Put them in new soil and kept them damp.

I'm wondering since we had such a mild winter here in Maryland last year, if that's why they survived.
I was very aggressive!

Have a question or two about the planting procedure I outlined above: namely, amending the soil when planting inground. I have read numerous times that, short of your soil being rock-hard clay or pure sand, it's best not to amend. This applies when you dig a planting hole twice the diameter of the container. Such a small hole creates a "saucer" which can hold water and lead to all kinds of problems for the roots. In addition, feeder roots growing through the amended soil may have a difficult time when they hit the native soil. Now, it's also been suggested that you can amend if you're amending a larger area. My questions (and I certainly mean no disrespect) are (1) how large must the area be if you wish to amend, and (2) wouldn't the feeder roots still encounter the same problems when they ultimately met the native soil?
Appreciate any responses.
gary

That's a great question, Gary. Ideally, you would want to amend an area equal to the mature root spread. But it is nearly impossible to guess exactly what that may be - roots do not necessarily grow in a perfect circle and depending on soil conditions, they usually just keep extending over the life of the tree. And very often, that is just not a practical approach in an already established garden.

If you feel you need to amend, do so over the largest area you can manage. And to avoid any 'bucket' or 'saucer' issues, dig a very wide but rather shallow planting hole and set the rootball high (above grade). Mound the backfill up to the top of the rootball but not over the top. Make sure the sides of the planting hole are very dished or sloped and roughed up (not smooth).

Feeder root will penetrate into the indigenous soil. It is just that if you make the planting hole too rich and appealing by amending, the roots are less inclined to extend properly and you risk them circling around in the original hole rather than extending laterally as they should. Roughing up the sides of the hole helps with this.

Thanks, gardengal48. Have followed your advice: wide planting hole, planted high and no amendments. Wish me luck!
gary

In some hard soils I have taken a pick to the sides of the hole and pried the soil loose so the roots and excess water has a place to go. That's a little more than just roughing up the edge of the hole, which works in most cases. The main thing you want to accomplish is to make it easy for the roots to explore out from the main root ball. Increasing the amount of interface works for me. You don't want a quick change from one soil to the other.
Mike

Thanks, gardengal48 and Mike.
I am also preparing to plant some Blue Pacific junipers and wonder if the same planting techniques apply. (Let me know if I should post this elsewhere, such as conifers or groundcovers.)
Have heard/read that juniper groundcovers like relatively infertile soil and the roots have no trouble penetrating clay. If true, there would be no need to amend soil. Right?
If amending is necessary, however, gardengal48 has recommended that it be done over as large an area as is feasible. I plan to place these junipers into an area 12' x 18' which is, for the most part, bordered by the south side of a house and a blacktop driveway. If I dig/amend this entire area and plant 4-5 Blue Pacifics (along with some perennials to fill in the bare spaces temporarily), should this accommodate the junipers' roots?
gary

gary, if you can get a shovel into the soil, then I'd just go ahead and plant the junipers.......no amending. Each juniper can be expected to fill about a 5' spread in time so space accordingly.

Junipers can be difficult to work around so I'd be cautious about the placement of other plants. And since the junipers stay so low, I'd be inclined to plant anything taller behind them.

Thanks gardengal48.
Got those junipers in the ground with no amending. Was planning on planting some perennials in the spaces between the junipers in the spring: coneflowers, black-eyed susans and other low maintanance, drought tolerant plants that are easy to divide. When the junipers begin to crowd them, can divide and transplant these plants in another sunny site. What hazards should I consider when placing these plants among the junipers?
(Also have a question regarding the crape myrtles I planted last month. Since this tree/shrub is not listed among the categories on this site, will you suggest one where I can post my question?)
gary

Probably Trees & Shrubs, but I can also help.
I have an OCD thing for anything red, which in addition to JMs, includes about 32 different varieties of CMs.

Other than the potential for crowding, the junipers can pose more hazards to you than to any perennials. They are pretty scratchy to work around and can promote phytodermatitis to those folks who may be sensitive. They are also big pollen producers if allergies are a concern.

Not to discourage you from using them - they can be great plants in the right setting - just wanted you to be aware that junipers are not necessarily the most user-friendly plants :-)

Crapes are generally considered to be shrubs, although they can grow to tree-like stature in appropriate settings.

Thanks again gardengal48 and CEFreeman.
I planted 6 Japanese maples (with 5 others overwintering in containers) and 4 Crape Myrtles last month. Three of the CMs ...Tonto, Natchez and Dynamite ... range from 4'-5' tall and their leaves are coloring nicely. On the other hand, Catawba is 8' tall; its leaves began dropping shortly after planting but that has stopped. What's surprising is that very tiny leaves are appearing on Catawba's branches. I assumed these trees were going into a dormant stage rather than putting out new growth. And since they produce flowers on new growth, these wouldn't be flower buds. And as I said, this is only happening on Catawba. Is this something unique to this particular cultivar? Is it a response of some kind to the initial loss of leaves? I'm a total novice to the world of trees and would appreciate any answers and advice.
gary