Outdoor growers on the other hand can use the seasons as a predictor of the ideal harvest t ime. In the Fall, once the length of day drops below 12 hours, the count-down to harvest will be begin. Weather conditons will affect the exact harvest day from year to year, but generally you can expect to harvest within the same two-week window each year. If you can avoid it, don't harvest during or immediately after a rainy spell. The best way to tell if the plant is ready is to examine the bud.
Many growers elect to pick each bud individually, as it reaches it prime.
When the plants are left in the ground, the resinous qualities of the plant may become more apparent. Frank and Rosenthal Marijuana Growers Guide pg 289, pg 295. Many cultivators prefer to pick some of their strains during this stage in order to produce marijuana with a clear cerebral, psychoactive effect. Robert Connell Clarke Marijuana Botany , pg 140. When the glands have swelled and the pistil has receded into the false pod, the bud is ready to pick.