Recreational marijuana is now legal in Maryland. ‘Expect a lot of fun.’

As the clock struck midnight on Saturday, Maryland became the 21st state where recreational cannabis sales are legal.

Eager cannabis users camped out in the Green Ridge State Forest at a music festival that marked the occasion with a countdown to a 12 a.m. “bong drop.” The Maryland Marijuana Justice advocacy group gathered 30,000 marijuana seeds to hand out for free Saturday.

And dispensaries invited DJs and food trucks for the first day of recreational sales, where customers 21 and older with a driver’s license or other government-issued ID can...