The best way to know whether your marijuana plants are ready for harvest is by observing the development of the trichomes on the buds. Trichomes are small semi-transparent lollipop-shaped sticks that appear all over the flowers. In other words, the so-called resin is formed by trichomes and it's there that the plant's cannabinoids are. When 30 % of them turn amber, it means your buds are ready to be harvested. Other telltale signs that could also help you are these:

• The resin production has reached its peak
• The buds have stopped growing
• The secondary leaves have started to discolour and most main leaves have fallen

More info: When is the best time to harvest your cannabis?