Understanding the growth cycle of a cannabis plant will help you appreciate what it takes to cultivate quality marijuana and make you a better gardener if you're growing your own crop. Cannabis is an annual plant, meaning it completes its entire life cycle within one year, and it needs different amounts of water, nutrients, and light during the various growing stages. For your convenience, here we touch on the basics of the growth cycle of a cannabis plant.
A cannabis seed will remain dormant until it becomes saturated with water long enough (24 hours to 14 days) to germinate and sprout a taproot, beginning the first stage of the plant's growth cycle. This taproot grows down, attaching itself to soil so it can absorb nutrients and create a stem that breaches the earth's surface and begin the next stage of the life cycle.
The emerging stem becomes the young cannabis seedling over the next 2-3 weeks. At first, two embryonic (cotyledon) leaves grow from the stem to take in the sunlight the plant needs to develop. The roots and first “true leaves” (which have the iconic fan shape we associate with cannabis) grow rapidly during this time, and as the seedling grows the leaves of cannabis plants develop more fingers until each leaf has five or seven fingers.
Once the cannabis seedling has established a root system and its first few leaves, the growth accelerates rapidly. The stem grows taller and thicker, foliage becomes larger, and the plant produces nodes which generate new branches and leaves. Cannabis plants in their vegetative phase benefit from lots of sunlight (some cultivators provide 24 hours of light), consistent watering, and nutrient-rich soils heavy with nitrogen as they grow to heights of 2-5 ft. over the next 2-10 weeks.
Sometime during the vegetative stage (anywhere between 1-5 months) cannabis plants enter what's known as the pre-flowering phase. This is when you can determine the sex of the plant; males produce a small sac at the nodes and none of the flowers that female cannabis plants are famous for.
A reduction in light duration to 12 hours per day triggers flower production, the final stage of the female cannabis plant's growth cycle. This stage can last 6-8 weeks as flowers develop, and once you can see the thick coat of resinous trichomes on their surface, it's time to harvest the crop.