Epiphyllums can grow to be quite large (several feet in Diameter) it's in their genes. But you can trim out old growth that has become shriveled. The older growth will not produce blooms any more and can become a drain on the plant. Trim the old stems out about 2 inches from their starting point. this gives the cut room to die back and callus over naturally.
Epis look best in hanging baskets for the most part sense they are epiphytic in nature or at least their background is. A 14 inch basket is as big as I would ever go. That would be for a really big specimen. Just remember sense they are epiphytic They don't like to be over potted.
The best thing you can do is contact some growers in your area and ask their advice.

Bob

oh man, I was just at the Huntington yesterday and if I had seen this before going I would have taken a pic of the palm eating epi. It's about 10 foot tall and maybe 5 foot around completely covering an old dead palm stump.

I do like to keep them in hanging baskets. I actually have most of them on pulleys so that I can lower them down to have a good look. The one which prompted this note was the last to be put into a basket. All the others fit quite well into 12 inch baskets but this last one just has a big root ball.

Well, I will see how it does and will try to trim back some of the older shoots. Thanks for the advice.

I'll bet that palm-eating epi was one of the "Queen of the Night" ones.

a.m.