Our patch is in its fourth year and going strong. Haven't notice much expansion, but haven't really fertilized either. Do cut all of the ferns before first freeze and mulch. Texas winters (yes, I know, laugh!) don't phase them at all. We only harvest for three or four weeks and then let the rest grow to fern - this is how they store food for next year's growth. Not much makes it to the house though - it is sooo yummy right out of the garden!
