There are two key things you should know about the cannabis industry, particularly in the U.S. First, it's still only in its early innings. Second, the potential market is huge. Those happen to be two characteristics that bode well for long-term investors.

Some cannabis companies are in especially strong positions to succeed -- and deliver great returns along the way. Here are three of the best marijuana stocks to buy in May.

Cannabis leaf on top of $100 bills

Image source: Getty Images.

Ayr Wellness

Pot stocks aren't known for being inexpensive. However, Ayr Wellness (OTC:AYRW.F) just might come as close to being a bargain in the cannabis industry as you'll find. Its shares trade at only a little over three times expected sales, well below the levels of other leading U.S. multi-state operators (MSOs). 

Ayr recently opened its 50th cannabis dispensary nationwide. The company expects to launch at least 10 more dispensaries by the end of this year. And Ayr is targeting some of the fastest-growing markets in the country.

The company operates in Arizona, Massachusetts, and Nevada, each of which has strong adult-use recreational marijuana markets. It's a key player in the expanding medical cannabis markets in Ohio and Pennsylvania. Ayr's recent acquisition of Liberty Health gave the company a significant presence in Florida, which is also home to a robust medical cannabis market. The company will also move into New Jersey this year once its pending acquisition of Garden State Dispensary closes.

Ayr expects to generate revenue of $725 million in 2022. If the stock continues to trade at its current price-to-sales multiple, that kind of sales growth could lead to Ayr doubling in the not-too-distant future.

Cresco Labs

Cresco Labs (OTC:CRLBF) stands out as another MSO with a relatively attractive valuation. Its shares trade at around 3.7 times expected sales.

Like Ayr Wellness, Cresco has grown tremendously through acquisitions. Its purchase of Origin House early last year vaulted the company into a leadership position among cannabis wholesalers. Cresco's acquisition of Bluma Wellness, which closed in April, gives the company a foothold in Florida's fast-growing medical cannabis market.

The company isn't finished gobbling up other players yet. Cresco's pending acquisition of Cultivate would make it a major contender in Massachusetts with a top-three market share in the state.

Look for plenty of organic growth, too. Cresco is one of a handful of cannabis companies poised to cash in on New York's legal pot market. The Empire State recently legalized recreational marijuana. Cresco is one only 10 operators currently licensed for vertical operations in New York state.

Planet 13 Holdings

Planet 13 Holdings (OTC:PLNH.F) isn't a typical cannabis company. Sure, it shares a lot in common with others in the industry. However, the company's SuperStore sets it apart from the pack.

Located just off the famous Las Vegas Strip, the Planet 13 SuperStore is a one-of-a-kind tourist destination. The store features interactive floors, 3D visuals, an aerial orb show, and -- of course -- lots of cannabis products to buy.

Planet 13's Las Vegas SuperStore won't be one-of-a-kind for much longer, though: The company is scheduled to launch its Santa Ana, California, SuperStore this summer. Planet 13 believes that it will be able to replicate its success achieved in Vegas in California and potentially in other destination sites across the U.S. in the future.

Don't be fooled by Planet 13's Q4 results missing analysts' expectations. Revenue grew briskly despite a lingering impact from COVID-19. Most importantly, the company had its best month ever in March. With Las Vegas bouncing back and the California SuperStore on the way soon, now is a great time to consider buying this unique pot stock.

This article represents the opinion of the writer, who may disagree with the “official” recommendation position of a Motley Fool premium advisory service. We’re motley! Questioning an investing thesis -- even one of our own -- helps us all think critically about investing and make decisions that help us become smarter, happier, and richer.