Pruning Japanese Maples

I have 2 large Japanese Maple plants that I am overwintering for a client in my greenhouse. I know they need to be cut back, but am hesitant on just how to go about it or how much to take off. I am posting a picture that I took of them last night; I'm hoping you can see how each plant is "growing" in regard to the stem, etc. The yellow one is really just one long stem with side stems. The other one looks to be a bit more tricky, as it appears that the top growth stem has been cut out (or just never grew more from the top) and has really heavy side growth. Both plants are about 4 feet tall, and getting to be extremely leggy, but are both blooming heavily. Arghhhhhhhh............what to do??? I know with my own red one it was about half died out/dried out and I just hacked the whole potful back to about an inch above the soil and said "live or die, punk, it is up to you". Grew back really nice and full. However, this was several plants in one pot. These are just one plant per pot. Any suggestions on how to do this properly and not kill it? Treat it like it was one of my own?

Thanks.

Hi Anna,
are these perhaps Abutilons? Kind of hard to tell, but that is what it looks like to me. I have several, they all live outside and bloom year around here. I prune them back whenever the mood strikes me. I have cut them down to within a foot of the ground with no ill effects, but usually I just prune to shape. I have one out front that is an actual tree and that is really leggy and never bushes, and I really butcher that puppy back to just little nubs off the trunk when it gets to where it is almost pushing itself over off the wall. The only reason I don't prune them in the winter is because the hummingbirds feed off them all winter and I don't have the heart to take away a food source.
Hope that helps. :~)
Donna

Definitely not Japanese maples with those flowers! I would guess abutilons as well, those have the common name flowering maples.

Here are a few sites with info on pruning abutilons, hopefully you'll find these helpful (there are lots more if you google "pruning Abutilon")
http://www.thegardenhelper.com/abutilon.html
http://www.whiteflowerfarm.com/growguide-1.html
http://www.logees.com/ftg/CULTURAL-abutilon.asp

I thought the 2 terms were synonymous...........abutilon and Japanese maple. Sorry.

No, Japanese maples are in genus Acer with all the true maples. Abutilon is in a separate genus and not at all related to maple trees. They got the common name flowering maple because of the shape of their leaves but botanically they're not related to maples at all, they're in the same family as things like hibiscus and hollyhocks.

Sorry Anna, got sidetracked and did not finish posting. I wanted to show you the pic of how overgrown my yellow tree can get and then show you how drastic I have pruned it, actually, a lot more then in this picture. I do this every spring/summer/fall as needed and it just comes back bigger and bigger. I do the same thing with all the others I have that are not under an overhang like this one and have never had any ill effects. The ones out back get so tall I just lop the whole top off to the height I want. Both the pics are a few years old, the tree is in the ground now and seems to actually thrive when I drastic prune, like in this pic. Your temps are so cold though, I would say wait until it warms up and then prune them to whatever you think they need.
These are a lot hardier then people give them credit for.
Donna

Ummm..........Donna..............that is a STICK!!!!!!!!!!!!! LOL

The ones I posted the pic of are in the greenhouse, I think if I'm gonna prune and have them respectable looking for their owner, I should do it now.

OT, Donna. What is the fantastic plant that is growing in-between the stepping stones.

LOL, Anna, I know, and I sometimes cut it back even farther! These are some tough puppies, I tell you!

Christi, it is dichondra between the stones. It was gorgeous and I loved it, but I could not keep the weeds out of it! It became a nightmare to keep up and keep wet enough, and I finally just sprayed it with Roundup and started over with regular grass. It is ok looking now, nothing like the dichondra but acceptable. Besides, I am never out front to see it so I can live with it. LOL

At least a couple of the references I found said they could be pruned back hard. I'm not sure if you want to freak out your clients though when they come to pick the plants up again, maybe a bit of more judicious thinning would be better in this case!