root pruning is very old school ...

current thought is not to stress the heck out of them now.. and do it again at transplant ... when the time comes.. just do it ...

we are only a few weeks from the high heat of summer... in my z5 MI ... i am basically stopping all transplanting.. and holding stock over until fall ...

you would dig about 6 inches out.. from what you planted ...

if you tell us where you are.. someone might be more specific on dates ...

if you have to move them.. just do it ... but my suggestions is for the best time to move them ...

ken

Ken
Thanks for the suggestions. I'm just outside Roanoke, VA. Despite the mild weather thus far, history tells me we're in for some blistering hot days through July and August. (And September hasn't been exactly comfortable as of late.)
I usually do dividing and transplanting of perennials (hostas, for instance) in late September to mid-October.
The crape myrtle's planting containers were about 12" in diameter; the planting hole I dug was 24" wide and as deep as the container. (Actually, not quite as deep since I planted them just a bit 'high'.) Please bear with me: I want to make sure that I understand. You suggest digging 6" out from what was planted. If I go out 6" from the base of the trunk, I'll have a root ball the same size as it was in the original container. If I go out 6" from the original root ball (as it was in the container), I'll have a root ball about 24" in diameter. Of course, If I go out 6" beyond the planting hole I dug, I'm looking at a diameter of 36". Big hole! : ) I'm a bit slow sometimes; would appreciate if you'd clarify which of my interpretations is correct.

Ken, can you explain why root pruning is old school? Everything I've read from extension services has said that it improves survival rate after transplantation, especially when you can't provide adequate watering.

1. I believe this link will answer your first question: Planting a Tree or Shrub

2. & 3. Crape myrtles are tough and need very little babying. You can add trunk diameters (if multiple trunks) and get a rough idea of the rootball size from the table found here: Generic Rootball Size Guide

4. Root pruning is not necessary for crape myrtles. It might be beneficial for some much more finicky types of trees/shrubs, if you could do it far enough in advance. I see no benefit in the case of crape myrtles.

I would have transplanted the crapes in March or April prior to their coming out of dormancy for the best outcome.

But, since yours have not been in the ground all that long (and probably are not really established yet), you could probably get away with moving them now PROVIDED you trimmed back some of the new growth (maybe 2/3 of the NEW growth?) and water, water, water them all summer, deeply at least once a week.

Thanks everyone.
I've calculated the rootball diameter and depth for transplanting, using the guide provided by brandon7 earlier in this thread and will be listing the results.
But first .....
yesterday,a neighbor heard about my plans and said that I don't need to transplant. According to him, the crape myrtles are getting 'all the sun they need'. Being new to crape myrtles, I have no basis to disagree with him. I'd like to get your take on the situation.

'Tonto', the smaller of the two, gets full sun until about 2PM, daylight savings time(so actually 1PM based on the sun). By 3PM (true 2PM), it's receiving no direct sun. Is this, as my neighbor claims, sufficient sun for the crape myrtle to thrive and bloom? I was under the impression that they were sun lovers and needed all day or near all day sun.

I believe they would probably do better and be healthier and more full if given more sun. Whether or not they will have "enough" sun exposure in their current location, it's hard to say. My guess is that they would survive with the light they have now, but not not reach their full potential.

Do NOT "(trim) back some of the new growth" if you do move them!

After all the responses, I am leaning toward transplanting (for more sun) in the fall. I understand transplanting now is a possibility but am concerned about the stress the plant may experience during the summer.

brandon7: I used the rootball guide you kindly provided and calculated the diameter and depth of the rootball I will need to dig when transplanting. I'd appreciate it if you would look over my figures to see if my interpretation is correct.
(Both crape myrtles have three trunks coming out of the ground close together. I calculated the diameter with C = d x pi)
1. 'Tonto': The diameter of the three trunks are .68", .6" and .52", respectively. These add to a 'total trunk diameter' (that's what I'll call it for these purposes) of 1.8". Based on the guide, I'll need to dig a rootball whose diameter is 25" and depth is about 12".
2. 'Catawba': Trunk diameters are .83", .83" and .64", respectively, resulting in a 'total trunk diameter' of 2.3". According to the guide, I should dig a rootball with a 32" diameter and a depth of approximately 14".
Are these figures in the ballpark?
Thanks

Yes, you did the calculations correctly. These are just rough estimates (and may not be ideal for all species), but should work great for your crape myrtles.

I would wait till they go dormant in the winter. They are pretty tough, but I'd still wait till dormant. Much less stress...

Back again. I decided, after reading the suggestions_ and no offense to anyone_ to wait until late September to transplant.
I'd appreciate any suggestions regarding pruning that should be done before transplanting. (I'd like to train the plants into a 'tree', rather than a 'shrub', form.)

why would you want to cut off all the branches.. before you cut off all the roots...

one stress this fall.. move it...

once re-established.. then start cutting off its food making machines.. the leaves ....

ken