Hemp seeds are imported from the Netherlands, from Canada and from most marijuana growing countries. Hemp and marijuana grow well, from Okinawa to Hokkaido. There's plenty of rainfall and the cooler climate of the mountains is no problem, as marijuana also thrives in the mountains of Colombia, Mexico, Nepal and Switzerland. People grow it on wooded hillsides, in abandoned fields, hidden in bamboo or goldenrod. Increasingly marijuana is also cultivated at home, even in cities.
Many Japanese growers read sophisticated foreign literature about growing indors under lamps.
The information is freely available in numerous books and websites . Electricity may be expensive in Japan, but so is weed if it's purchased on the black market. Most of the home cultivated drug hemp is never sold. Even though the police is less interested in marijuana users than in speed users and their organized crime links, selling to people who later get busted for possession and snitch on you is still a good way to get yourself into a lot of trouble in Japan. So most growers take the safe route and only produce for their own personal use.