Basic polytunnels add three or four weeks to each end of the season, which is often the difference between finishing a photoperiod CBD strain and composting it green. Heat builds fast on sunny days, so roll up sides or a fan are not optional, and mould pressure rises in autumn without airflow. Greenhouse specific notes, including light dep tarps for forcing early flower, are gathered on https://calmcbdseeds.com from a handful of northern growers. It is the cheapest upgrade for anyone above fifty degrees latitude.