It is extremely important to do field testing once plants are a few weeks into flower to ensure THC levels are below the required amount (0.3% in most states).  By regular testing, harvest timing can be planned in order to reach highest CBD levels while staying within legal limit of THC. It is recommended that you begin testing your field 2 weeks into the flowering cycle every 1-2 weeks until harvest so that you are very familiar with where your THC levels are at. Please be sure to choose a reliable and consistent accredited lab to work with so that you can be assured of the THC levels throughout the season.