I try not to do any transplanting between the 4th of july and Labor day, the weather's usually awful, I get sunburned, the plants get stressed, and the chance of losing something is doubled.

I usually shoot for half-way between the trunk and the spread of the branches- I will be generous with soft-rooted things like azaleas, and a bit chintzier with tougher things.

when things start to wiggle a bit, run the hose over the cut, guestimate the size of the plug, and go dig the hole to recieve it, and fill it to the top with water.

THEN go lift the plant, knock about 1/3 of the dirt off the roots, and move it. I always like to add a scoop of mulch to the very bottom of the hole... if there's still water in the hole when you get back, you have 'heavy' (clay-bearing) soil, and it's not a bad idea to break it up a bit more, and mix ground mulch and compost into the bottom of the hole.

I purchased vervenas for my windowboxes but the boxes are not as deep as the vervena plants. I have planted them but they seem to be struggling. Would it be ok to cut the roots back to fit the pot and fill the pots again with a rich healthy soil. Sort of a bonsai kind of thing???
Or do they need to be planted at the depth they were purchased?