Sorry for the late response. I am concerned about rot also with plastic but I leave the ends open until the first heavy snowfall (usually later in December) to allow the soil to dry out further. I also leave a couple of small vents in the cover against the house foundation. I am starting to interplant bulbs with the cacti so see if the dry soil will allow me to grow a broader range here in zone 5. Suggestions for candidate bulbs are welcome! Regards, Phil From Michigan's zone 5 but currently in St. Louis where it feels as cold as Michigan today.