What color were the ferns? If they were light brown, fully dead, then it indicates that the plant is dormant, and it is fine to mow the ferns now. If they were still in the process of dying back, such as a bright yellow, then it might have been better, but not critical, to wait just a bit more, until the ferns wither and turn light brown. As I understand it, the yellow ferns, although no longer making food, still contain nutrient energy to transport to the crowns before the ferns totally die back. It’s best not to cut down green ferns, as they are still making food for the plant; if yours were still green, then hopefully the plant, at this late date, has enough food to get by for the winter and start up again in spring; there might be a chance, though, that the spears next year might be weaker, until the plant can recover; if this is the case in spring, you might avoid harvesting that year, so that the plant can catch up on food-making. Hope this helps!
What color were the ferns? If they were light brown, fully dead, then it indicates that the plant is dormant, and it is fine to mow the ferns now. If they were still in the process of dying back, such as a bright yellow, then it might have been better, but not critical, to wait just a bit more, until the ferns wither and turn light brown. As I understand it, the yellow ferns, although no longer making food, still contain nutrient energy to transport to the crowns before the ferns totally die back. It’s best not to cut down green ferns, as they are still making food for the plant; if yours were still green, then hopefully the plant, at this late date, has enough food to get by for the winter and start up again in spring; there might be a chance, though, that the spears next year might be weaker, until the plant can recover; if this is the case in spring, you might avoid harvesting that year, so that the plant can catch up on food-making. Hope this helps!