Watertown planning officials will hold a public hearing Wednesday to discuss the possibility of imposing a one-year ban on opening medical marijuana dispensaries in town. The moratorium is gaining popularity in Massachusetts communities since Attorney General Martha Coakley deemed the approach lawful earlier this year. It would give town officials until June 30, 2014, to figure out where dispensaries should be located, according to the Watertown Planning Board. It would be enacted by amending zoning laws. The hearing will take place at 7 p.m. at Town Hall, 149 Main St. For more information, visit the town’s website, www.watertown-ma.gov.