I am providing a link to a little additional information on infrequent use. While this is from NORML
(an advocacy group) it has the citations for confirmation. The fact that "Hair tests are more likely to detect regular than occasional marijuana use" is a long standing problem(?) with the test.
Believe it or not, your hair color probably is in your favor. A major problem with HDT is that those with coarse dark hair are more than twice as likely to test positive (for all substances) than their fair haired counterparts.
Additive, DuPont (2008)
found that hair testing was "remarkably effective in
targeting the heavy, frequent user of illegal drugs rather than the occasional user of illegal drugs..." and relating to marijuana noted "hair testing is unlikely to be positive for marijuana until the tested student has used marijuana at a rate of about twice a week in the prior 90 days. (p. 8)"
The 2008 study is consistent with an earlier (2006) that appeared in the Journal of Forensic Sciences
which concluded "Drug testing technology that detects the residual presence of cannabinoids and/or their metabolites in the hair typically fails to identify occasional marijuana users."