I'm planning on enclosing a porch with glass. I will also add skylights.
Someone has told me that low E glass will stop all UV light which is
necessary for plants to live. If that is true, I'll not get the Low E
glass, but otherwise, I'd like to have it. Anyone with knowledge of this
matter?


They'll do just fine. They may see a net energy production decrease of a
couple of percent, but unless you're right on the very fringes of what the
plant needs, it will be completely negligible. The "absorbtion maxima" of
chlorophyll (where the light does the most good) are in the blue and red
areas, and the absorbtion is falling off pretty quickly at 400nm, where the
UV area is just beginning. Here's a plot:
http://www.biologie.uni-hamburg.de/b-online/e24/3.htm

steve