WASHINGTON — It’s not the promise of prompt delivery that has residents of Washington, D.C., spending fifty bucks for nondescript glass jars, nor is it the small jars themselves, which resemble something found on the bottom shelf of a Dollar Tree.

It is the unmentioned “gift” that a local online upstart, Trendingleafs, tucks inside each jar: fragrant clusters of Grape Ape, Purple Kush or Woody Harrelson OG. Or it might be cannabis-laced snickerdoodles or a vial of Lemon Haze concentrate.

The explosion of small businesses openly distributing thousands of such mind-altering “gifts” daily throughout the capital is not what Congress had in mind when it banned regulated sales of recreational pot in the nation’s capital, defying the will of local voters. Instead of shutting the legalization movement down, however, Congress has helped make this often-staid East Coast city the Wild West of recreational pot distribution.

Nowhere is more pot sold so openly and publicly without any of the rules and regulations that elsewhere have come with legalization.

Hawkers of bud here will tell you they are not selling it, but giving it away. They bestow gifts on strangers who make ostensibly legitimate purchases of other goods from them — a bottle of juice, for example, or a bag of cookies priced at $50, which happens to be the going rate for a delivered dime bag. Sometimes these companies forget to deliver the item they nominally sold. But the customers generally don’t complain, as long as the gift arrives.

Selling a token container of food or a pair of socks for fifty bucks and attaching a free bag of pot is technically illegal in Washington. But local officials are hardly cracking down.

Congress’ action left city officials unable to impose any oversight on the recreational pot trade, which local voters legalized by referendum in 2014. The congressional ban, adopted shortly after the referendum, prevented the city government from using any of its funds to implement legalization. Even holding a hearing on setting up a regulated legal market could constitute a felony.

The result has been to turn Washington into the country’s biggest experiment in largely unregulated marijuana selling.

“This is an enormous market over here,” said Joe Tierney, who plays a crucial role as the author of a blog called the “Gentleman Toker,” which guides smokers to start-ups providing pot gifts and posts exhaustive reviews. He counts 30 companies taking delivery orders through well-established web sites, and another 300 or so upstarts selling over social media on any given day.

“It is the only recreational market on the East Coast,” Tierney said. “People come up to buy all the way from South Carolina. They come down from Pennsylvania, Jersey, Ohio. Even companies out West are looking at how can they get in on this crazy market. It is a very interesting time.”

Local law enforcement hasn’t turned an altogether blind eye. Occasional raids do take place, typically directed at the most flagrant operators.

“The ones we come across are usually pretty brazen,” said Lt. Andrew Struhar of the Narcotics and Special Operations Division of Washington’s Metropolitan Police Department. “There are so many of these companies that we wind up just scratching the surface,” he said.

“This speaks to the fact that you can possess and use marijuana in your home, but there is technically no legal way to get it other than grow it,” Struhar added. “A lot of these companies are trying to fill a void, and they are trying to figure out a way to do it cleverly and legally.”

To some, the thriving industry of start-ups openly selling pot online, at head shops and at almost daily publicly advertised pot flea markets in bars, clubs and private homes throughout the city has become a symbolic snub of Washington’s congressional overlords.

On a recent weeknight at the XO Lounge, a few blocks north of the White House, each of three floors was packed with vendors collectively selling enough weed to keep the neighborhood of lobbyists and deal makers high throughout the Trump administration. House music thumped. The air was thick with smoke. The event was open to anyone who clicked on an easy-to-find Eventbrite link. Ten bucks or a toy donation for local kids got you inside.

Across town in Adams Morgan, the Funky Piece head shop alerts entering customers with a curbside sign directing them to ask about the free “gifts” that come with purchase of smoking accessories.

Even some legalization proponents worry Washington’s inability to impose any regulations over its rapidly emerging pot market creates public health and financial problems. The city lacks any of the safeguards in place in states that have legalized, such as those that will govern sales in California starting in January.

Marijuana here is not tested for dangerous pesticides or mold. Nor is it sent to a lab for an assessment, which buyers can use to gauge potency and potential psychoactive effects. The city is not collecting tax revenue on the sales, which could be used to fund public health programs.

At the same time, the path the city has reluctantly forged has kept it relatively free of corporate marijuana players, who have an outsize role in influencing marijuana rules in the states that have regulated pot sales. The entrepreneurs thriving in D.C. are all small operators, and they are a diverse group.

“It shows how you can have legalization without mass commercialization,” said Adam Eidinger, who led the 2014 legalization campaign. “There are some things about it that are really nice.”

And some who have studied markets elsewhere question whether the consumer protections other states promise are overblown.

“I’m not sure how valuable a lot of those regulations in other places are,” said Mark Kleimann, a professor of public policy at New York University. The product testing that some states require lacks rigor and may remain unreliable as long as the federal government refuses to get involved in setting standards, he says.

Critics of Washington’s situation typically direct blame at one man, Rep. Andy Harris, the Maryland Republican who wrote the budget amendment prohibiting the city from regulating the sale of recreational pot.

“One congressman from Maryland single-handedly created the least effective system in the U.S. for guarding against any challenges marijuana presents,” said John Hudak, a senior fellow of governance studies at the Brookings Institution.

Harris, who is a medical doctor, says he has no second thoughts.

The ban on recreational pot sales in Washington, he said, “sends a powerful signal to the rest of the country that other jurisdictions should think twice about this. It is a dangerous substance. We have not done the medical research necessary to outline what the dangers are.”

He says Washington is in a mess of its own making.

“I’m shocked they are not doing something about this,” he said. “They could choose to enforce the law.”

Yet even Congress is sending mixed signals on pot — maintaining Harris’ ban, but also keeping in place a prohibition on federal drug agents raiding medical marijuana businesses that operate legally under state laws. The restrictions on the Drug Enforcement Administration so far have been kept in place despite aggressive lobbying by Attorney General Jeff Sessions, who wants a free hand to go after legal pot.

In some ways, says Kleimann, Washington’s situation is a workable compromise — legalization without the proliferation of marijuana storefronts and marketing campaigns that in other jurisdictions create a constant temptation.

In Washington, Kleimann said, marijuana is easy to find. But at least you have to look for it.

“I like cannabis being available to people who want it,” he said, “without entrapping them into substance abuse.”