Cannabis may be legal in California for adults 21 and older, but it remains a highly regulated plant. Before growing at home, residents should understand state law, local rules, landlord or homeowners association restrictions, safety issues and the impact a grow can have on neighbors. Understanding Local Cannabis Growing RulesUnder California law, adults 21 or older may grow up to six cannabis plants at home. California allows property owners to ban cannabis use on privately owned property, and renters should check their rental agreements for restrictions. Cannabis plants should not be treated like ordinary ornamental landscaping.