So if it takes your system 30 days to be clean of weed then your body will not start growing clean hair follicles until 30 days after you stop smoking pot! On average hair grows at a rate of .5 inches per month.or a first time pot user, thc will remain detectable in the system for a period up to 7 days. For some casual weed user who have smoked weed 2-3 times each week, thc can be detectable for a period up to 21 days. Chronic users who smoke pot everyday can expect to excrete thc toxins for up to 90 days.