A bill in Colorado would set a statewide limit of 12 marijuana plants per residential property. Pictured: A marijuana plant flourishes under grow lights at a warehouse in Denver. (Ed Andrieski, Associated Press)

Colorado looks to ban co-op marijuana grows to block black market

Supporters say criminals are hiding under a Colorado law that allows medical marijuana patients to have as many pot plants as their doctor recommends, then selling that pot on the black market

DENVER — Colorado may ban collective marijuana growing under a bill that calls some patient-owned marijuana grows a “public nuisance.”

A bill up for its first hearing in a House committee Monday would ban co-op pot growing by setting a statewide limit of 12 marijuana plants per residential property.

Colorado currently allows medical pot patients to grow up to 99 plants, far beyond other marijuana states, and it also allows recreational users to group their allotted six plants into massive co-ops, entire greenhouses of pot that aren’t tracked or taxed.

The large-scale grows are inviting federal scrutiny because it’s too hard to tell if those plants are being legally sold, not sold on the black market, said Rep. KC Becker, a Boulder Democrat who is sponsor of the bill.

“Colorado has a target on its back in terms of these large-scale grows,” Becker said Monday.

She called Colorado’s generous plant limits a “big regulatory loophole” for black-market drug operations.

But the change would effectively force some medical marijuana patients to buy from a licensed grower instead of growing their own plants.

Colorado has about 19,000 medical marijuana patients whose doctors have recommended more than six plants. Some cannabis treatments, especially oils used by people suffering from frequent seizures, require great quantities of raw marijuana to produce.

Patient advocates say increased tax revenue is the real goal of the change.

Though medical pot in Colorado is taxed at just 2.9 percent — far lower than recreational pot taxes, which start at about 37 percent — the state still made more than $12.8 million in medical pot taxes and fees last fiscal year.

The change would also affect recreational pot users who band together to grow pot, sometimes to share expenses, sometimes because they prefer not to grow the plant at home. Becker pointed out that collective pot growing could still be allowed, just not on property zoned residential.

The bill would make it a felony to have too many marijuana plants at a single residential property. A fiscal analysis prepared for state lawmakers gave no estimate how many people may be charged with the crime.