Image caption The WeGrow founder believes the marijuana industry will grow despite the federal ban on the substance

A retailer selling tools to grow cannabis has opened in the US capital, just a few miles from the White House.

WeGrow sells plant food and lighting - but no cannabis or seeds - to help cultivators grow medical marijuana.

The chain, dubbed the "Walmart of weed", launches its latest outlet just as Washington's medical marijuana laws come into effect.

Medical marijuana is legal in 16 US states and Washington DC to treat conditions from back pain to HIV/Aids.

Also on Friday, officials from the District of Columbia were due to announce who is eligible to apply for a permit to grow and sell marijuana for medical purposes.

Changing people's minds?

WeGrow's founder says he hopes his company will help create a "green rush" by selling the equipment needed to grow cannabis at home.

"The more that businesses start to push the envelope by showing that this is a legitimate industry, the further we're going to be able to go in changing people's minds," Dhar Mann told the Associated Press news agency.

Image caption The shop does not sell seeds or cannabis but has plant food, vitamins, ventilation and lighting

But despite medical marijuana laws, and decriminalisation of the drug in 14 states, federal law still bans its cultivation, sale and consumption.

Attitudes appear to be shifting. Almost 7% of Americans said they used marijuana in 2010, up from 5.8% in 2007, according to the Substance Abuse and Mental Health Services Administration, a federal agency.

Last year, a Gallup poll showed that half of those asked thought cannabis should be made legal, and as much as 70% supported medical use of the drug.

Many advocates for the legalisation of marijuana say the move would save money and improve efficiency in courts and prisons.

But the Obama administration has cracked down on medical marijuana dispensaries, leading some states to either delay or scale back their programmes.

Kevin Sabet, formerly a senior adviser to the president's drug czar, said that medical marijuana laws would encourage people to "make big money off an illegal drug".

WeGrow opened last year in Sacramento, California, and has since opened outlets in San Jose, California; and in Flagstaff and Phoenix, Arizona.

"It's been a don't ask, don't tell industry," Mr Mann said. "Most people still want to hide behind that facade."

According to research done for the American Cannabis Research Institute, the domestic market for medical marijuana was worth $1.7bn in 2011 and could grow to $8.9bn in the next five years.