You are right. It is due to lack of light. If you can hang them outside during the day it would help them but be careful at first as you do not want to burn the leaves. Perhaps under 50% shading or only direct sun in the early morning and late afternoon.

Thank so much. I live in AR so going "outside" this time of year is not an option. When spring rolls around I will prune them back and slowly move them out doors to avoid burning them.

have an east or south facing window you can hang them in front of?

In the late Spring through Fall I keep the Boston Ferns on the front porch that faces east. I probably could put a couple of them in front of the front porch window and might try that next year. They stringy frons are not unappealing, just as long as the entire plant is not stringy. I have brought the ferns in before and by the end of the winter I have lost interest in keeping them watered and fed but this year I have made a consistent effort and it has paid off as most all of the original frons are still intact and actually got "greener" when I brought them in. They were getting a bit "yellow" in the late Fall. Here is a picture of them while on the front porch. They really do well in this area.
http://i274.photobucket.com/albums/jj270/ArkyGardener/091607Mums.jpg

Opps Picked up the wrong URL. Here is the picture.

{{gwi:597752}}