Kate,

Post some pictures. Pictures are definately worth a thousand words.

Without seeing any pictures though I'd guess your trees are rootbound. 5 years in the same pot is a long time. Being in pots the roots have no where to grow but around the pot (circling roots) and this will prohibit the tree from taking up moisture and nutrients from the roots causing leaf and/or branch die back.

If this *is* the cause you have two options.

One: you can repot the tree into a bigger pot. Choose an appropriate size that one or two sizes up. For instance, if your trees are in 1 gal. containers pot them up to 2 or 3 gal. containers.

Two: You can prune back some of the roots. This allows you to keep the tree in the same pot. If you do prune the roots cut no more than about 1/3 of the roots. You should also prune back an equal amount of branches. If you don't prune back some of the branches the tree will suffer more die back as there aren't enough roots to feed the leaves and branches. After you've cut back the rootball add more soil to the pot. Keep the tree in open shade for a couple weeks to let it recover from the stress and keep it cool. Keep the soil moist (not wet) and don't let it go dry. You may want to give the tree some kelp exract to stiumulate root growth, but do not fertilize at this time.

Another reason your maple exprienced branch die back could be late season frost. The frost could've happened overnight causing damage. If this is the case snip the dead branch and monitor the tree for additional die back.

Hope this helps,

Layne