UPDATED: April 2, 2019
In the late 19th Century, Americans and Europeans could walk to their local pharmacy and pick up a bottle of cannabis extract to soothe their stomach pain, headaches, insomnia, or any one of several every-day maladies that might be troubling them. However just a few short years later, in the early 1900s, that quickly began changing. Between 1916 and 1931, 29 states had outlawed marijuana, and in 1937, the Marihuana Tax Act was passed, and in 1970, the Controlled Substances Act effectively outlawed cannabis entirely.
The prohibition of marijuana didn't slow down America's love of the plant, however, and between 1973 and 1978, eleven states decriminalized cannabis possession. In 1996, California became the first state to effectively legalize medical marijuana when voters approved Proposition 215. Just over 20 years later, there are now more than 30 states in which medical marijuana is legal.
In December 2012, Washington State became the first state to officially legalize the recreational use of cannabis. Colorado followed close behind in January of 2013. Over the course of the next five years, an additional seven states joined the ranks, bringing the current total to nine states in which cannabis is legal recreationally. Keep in mind, however, that despite the fact that several states have legalized cannabis, counties may have their own laws. In order to ensure you are operating within the confines of the law, be sure to check any local ordinances regarding growing cannabis in your area.
Here are the current legal states, and their laws (as of April, 2019.)
Adults age 21 and over can possess, grow, and give away as many as six marijuana plants. Only three of the plants can be mature and flowering at any one time. (source)
Up to 6 plants per person, but no more than 12 plants per household. Plants must be grown within a closet, room, greenhouse, or another enclosed area that is equipped with a lock or other security device. (source)
As of July 1, 2015, Oregonians can grow up to four plants per residence, regardless of how many people live there (i.e. four adults in one residence does not mean 16 plants.) (source)
Despite the fact that marijuana is legal in Washington State, cultivation is currently limited to medical marijuana patients only. (source)
Up to six plants are allowed per Colorado resident over age 21, with as many as three plants flowering at one time. Beginning January 1, 2018, all residences will be limited to a maximum of 12 plants unless certain requirements are met. Be sure to check your local laws for specific details. (source)
Adults over the age of 21 may possess, grow, cultivate, process or transport up to 6 flowering marijuana plants, 12 immature plants, unlimited seedlings, and may possess all the marijuana produced by the plants at the adult's residence. (source)
As of July 1, 2018, adult cultivation in private of up to six marijuana plants (two mature and up to four immature) is no longer punishable by a criminal or civil penalty. Those who cultivate marijuana for their own personal use may possess at home the total quantity of their harvest. (source)
Adults over 21 may cultivate within his or her primary residence up to six marijuana plants, no more than three of which are mature. (source)
Adults over the age of 21 may cultivate no more than six plants, or a total of 12 plants per household. Cannabis plants may not be visible from a public place without the use of optical aids. Cannabis may only be cultivated in locations equipped with locks or other security devices. (source)
Possession of up to 2.5 ounces of marijuana is legal for adults 21 and older. Within a residence, adults may grow up to 12 marijuana plants and/or possess up to 10 ounces of marijuana (provided that any amount greater than 2.5 ounces is stored under lock and key). (source)