A petition to allow medical marijuana in Florida is now available for signing — but don't bother stocking up on fertilizer and grow lights.

The proposed constitutional amendment would not allow people to grow their own. Cultivation and distribution would be restricted to state-regulated dispensaries.

The decision — which reflects a growing trend in medical marijuana states — was part legal and part strategic, said Miami political consultant Ben Pollara, campaign manager for the initiative.

Ballot language allowing both home cultivation and regulated dispensaries could run afoul of Florida law that limits constitutional amendments to one subject, he said. Beyond that, regulated dispensaries help authorities keep tabs on who is growing, who is selling and in what quantities, Pollara said.

"We are trying to be pretty meticulous in setting a real system for the distribution of medical marijuana,'' he said. "We want a tightly controlled system.''

Calvina Fay, executive director of St. Petersburg's Drug Free America Foundation, is skeptical.

"Other states have found regulating to be a nightmare,'' she said. "They are ignoring the fact that it is going to cost a lot of money to set up a regulatory structure.''

The amendment would give the Department of Health nine months after passage to set up rules and begin registering dispensaries, patients and caregivers. If the state misses those deadlines, Fay said, "we are going to open the floodgates for anybody to sue.''

The proposed amendment is the work of United for Care, headed by Orlando trial attorney John Morgan, who has pledged his personal wealth to help it pass. The state division of elections approved the petition's format last week. So signing can begin, though the Florida Supreme Court eventually must review the ballot language.

The group needs almost 700,000 signatures from registered Florida voters to put the issue on the November 2014 election ballot. United for Care's volunteers and paid signature gatherers will hit the streets in the next few days, Pollara said. The petition is available at www.united forcare.org, where it can be downloaded, printed, signed and sent in by U.S. mail.

For the first time, the proposed amendment fills in details about how a Florida system might compare with laws in 18 states and the District of Columbia that permit marijuana for medical use.

Some states restrict use to people with specific diseases. The Florida ballot proposal lists HIV, AIDS, hepatitis C, ALS, Crohn's disease, Parkinson's disease, multiple sclerosis, cancer and glaucoma — but also permits use for any debilitating condition if a doctor says benefits "will outweigh potential health risks."

Legal possession amounts in other states range from Alaska's 1 ounce to Oregon's pound and half. In Florida, the Department of Health would determine the allowed amount.

The state's ability to enforce driving under the influence laws would not change. Public smoking could be banned, as could its use in workplaces and schools.

States that approved medical marijuana in the late 1990s and early 2000s usually allowed only home cultivation. Problems arose when caregivers were allowed to grow and possess pot on behalf of patients. Some lined up hundreds of patients and produced pot in large quantities, making it hard to punish trafficking.

In southern Oregon, "the black market exploded,'' said state lawmaker Peter Buckley. "People … put together 45 growers, each saying they were growing for four patients.''

His bill to better control distribution through dispensaries while still allowing home growing just passed the Legislature.

States that passed medical marijuana in recent years allowed for both home cultivation and dispensaries or dispensaries only. All told, 15 states allow home cultivation, some under limited conditions.

The need to get marijuana to sick people, and not the black market, has created many regulations — and some problems.

People with drug arrest histories usually cannot work in dispensaries. Other provisions require security cameras, quality testing and audits. Violators can lose their registration.

New Jersey passed a dispensary-only law in 2010, but its only dispensary recently closed because it couldn't acquire enough high quality pot. Delaware passed a dispensary-only law in 2011 but won't register any due to a U.S. Justice Department memo stating large-scale distribution violates federal law.

Parrish resident Robert Jordan grows pot for his wife, Cathy, who has smoked for 27 years to relieve symptoms of ALS. They lobbied during Florida's last legislative session for a bill that would allow home cultivation, "and we still prefer that,'' Jordan said. "I don't like losing control of what she gets.''

But the Jordans will be out on Manatee Avenue on Saturday, with stacks of petitions.

"God bless John Morgan,'' he said. "He has brought more attention to this than anyone else. We are working with him.''

Contact Stephen Nohlgren at nohlgren@tampabay.com.