I had a similar problem, I grew some little catpiss plants inside till they were about 12 inches tall, then transplanted them outside in june... september comes around, and they've grown 3 inches! the roots didn't even grow out of their original soil (although the soil around them was actually better, forest humus (sp?). So check a few things, nighttime temperatures, soil ph/moisture, and light. I'd suggest just repotting them, using a very fluffy soil mix and seeing how that works for ya.