Marijuana is legal in Massachusetts, but it will be at least another year and a half before retail shops are allowed to sell it.   It means – for now – the only way to get pot legally is with a medical marijuana card or by attempting something that’s becoming increasingly popular:  grow it at home.

“It’s people in their sixties, 21 and up, anyone and everyone wants to do it,” said Charis Dunn, who works at Boston Gardener in Roxbury.   She says since the law legalizing marijuana went into effect in December it’s been a struggle to keep the shelves stocked with supplies for growing it.   “We have back orders for people.”

One customer, who did not want to be identified, told WGBH News he’s spent $800 dollars for a home grow operation that includes a tent, lights, fan and exhaust system.   He set it up in a spare bedroom inside his Boston apartment and pointed with pride at the six plants he’s grown from seed.

“It’s a great little hobby.  I’ve enjoyed it every step of the way,” he said. The man did not want to reveal his identity because he’s worried the plants could make him a target for thieves.   He figures each one is worth about $200.

“If this was taken from my home there’s nothing that makes it legal or illegal except the person that possesses it,” he said.  “When it grows fully, it will have a high value and that could be easily turned into a street value with a simple burglary.”

Concern about the black market is echoed by Nicholas Vita, the chief executive officer of Columbia Care which runs medical marijuana facilities in Massachusetts and six other states.    He says he’s seen sophisticated underground operations develop when home grown pot is legalized.

“If you look at any market where there’s been an introduction of these programs,” said Vita, “you also see an increase in black market activity.”

He says home growers who flaunt the law can sell their product for less and don’t need to comply with the standards required for medical marijuana operations.    He says laws allowing residents to grow marijuana also make it difficult for police to trace its origin.

“Law enforcement doesn’t really know how to distinguish and they aren’t able to distinguish between a black market product that’s imported from Mexico or Canada or somewhere else and something that’s grown in Massachusetts,” said Vita.  “There’s no trait, characteristic or bar coding that would allow them to actually go back to the primary source.”

Vita stops short of calling for more regulations on home grown pot.  He says he just wants a level playing field.  He compares the practice to home brew beer.  Most people, he says, will decide the store bought variety is better.

Inside his Boston apartment the grower who does not want his name published is hopeful his marijuana plants will continue to thrive.  He says he was spending as much as $300 a week buying medical marijuana.

“I’m growing it just for my own medical consumption,” he said.  “It’d be so much better to have it for free.”