I'm not sure about repotting it now...as I'm not familiar with the weather out there. Here it would be fine, but my trees haven't started budding and will not for a couple of weeks probably. Assuming yours has leafed out, it might still be ok if it isn't too hot out there. If you don't keep watering it after transplanting, you will lose some new growth though (and everything if it is really small).

I would recommend repotting every 2 years, although every year would also be fine.

Here's a photo of my JM. It's 2 1/2 ft tall. Is it ok to put it in the ground?
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Most folks would probably say you should wait a little longer on that little guy. In my neck of the woods it can actually be better to pot them when they are young because the pots can get too hot in the summer if left in the full sun (like over 120 F). However, If I were you I would plant it this fall after the leaves drop if you are dead set on it.

IMO you can plant trees anytime as long it isn't too hot or if the ground isn't frozen. So, I guess it would be ok now if you really want to, but I think it would be safer to do it in the fall to give the roots time to get established before the growing season.

It's my understanding that it's safe to repot plants anytime, as long as provide plenty of water. I have repotted my Japanese maples throughout the year and haven't had any problems.

Is it true that trees that are potted doesn't grow as big and fast as trees that are grown in the ground?

JimmyJumbo,

That isn't true at all. Nutritional aspects would be the cause as well as how much sun a plant is given in terms of poor plant citing or good.

Re: "Potting Up"
Pot them up as needed. Don't put a small rootball in a large container, i.e., graduate into each container otherwise poor root formation will be established. Don't let them, specifically the root system, get overcrowded. Specifically so that it becomes entangled. To prolong the life of a plant in a pot, the roots must be pruned, "untwisted", and in general terms, cared for. There are other care aspects such as food, water, location, etc, but just remember that you are caring for something in an un-natural way. So adjustment to meet the cultural needs from 'climate to climate' (will be necessary).

Dax

I'd have to say that potted plants CAN grow slower and smaller than plants in the ground as evidenced in bonsai culture...but they can actually grow faster in pots provided plenty of nutrients, water, space, etc (perhaps not larger because huge pots would eventually be needed)

In general, trees grown in a container will grow slower and smaller than those of similar size planted at the same time in the ground. The reasoning is very simple - containers offer a restricted growing environment in terms of both root run, nutrient availability and water. If the roots are not allowed to spread freely, access soil nutrients as needed and receive adequate moisture, top growth will not develop as rapidly as those without such restrictions. How this manifests itself is not uniform for all trees. Some will elongate in height rapidly but fail to fill in well or fully; other will just slow their overall growth. Techincally, mature size is only limited by how far the roots are able to spread. Given a large enough container, ulitmate height will not be affected, however it is pretty near impossible to supply any containerized tree (except for some dwarfed forms) with sufficient root space to achieve this end.

The only concern about sizing when potting up relates to the potting medium. If it is too moisture retentive, a larger sized container will hold too much moisture and this cause stress, lack of oxygen reaching the roots and encourages root rot problems. If the container medium is sufficiently well-draining, potting up immediately to a larger size is not really much of a concern. I grow many of my trees in containers and use a very fast draining potting soil and pretty much always plant up to a long term size immediately without any problems.

The container gardening forum has active discussions regarding this topic as well as many recipes for your own, homemade potting soils for a variety of plant types.