Native Americans picked the plums for use in cooking, and early American settlers used them for jams and jelly.
"It's the end of the season and the start of a fall harvest," said Pat Vargo, vice president of Friends of Island Beach State Park, which raises money for and helps maintain the park between the ocean and Barnegat Bay. "People come from miles around just to pick these plums. They go crazy for this stuff."
Beach plums have endured the harsh weather and salty spray of the Atlantic Coast for centuries. Their existence was noted by European explorers as far back as Verrazano in 1524.
Notable patches thrive on Cape Cod in Massachusetts; Plum Island, a beach near Newburyport, Mass.; Plum Island, a small island off Long Island, where the U.S. Department of Agriculture has a research center; and a beach next to a wildlife management area in Delaware known as Prime Hook.
The shifting windblown sands help spread and expand the colonies. Their roots penetrate deep into the soil, and lower branches are often covered with sand. New roots often develop from those sand-covered branches.
The reddish-purple fruits don't grow much bigger than a thumbnail, and they're exceedingly tart. Picking and eating one right off a bush may well put you off them forever.
But cooked, simmered, and blended into jellies, jams, breads and alcoholic drinks, the beach plums come alive. Recipe books on sale for $2 at the festival have easy-to-follow directions and handy tips, such as "take the pits out before cooking," and "it takes about eight cups of plums to make a worthwhile batch of jelly."
Jelly and jam will be on sale at the festival, including a plum-jalapeno recipe whipped up by a Cape May group. Plum ice cream, which tends to sell out fastest, will also be available.
This season has been a good one for the plums. Although many spots have already been picked clean by park visitors, birds, and small animals, there are still plenty of plums left in other spots.
Beach admission is free on Sunday, but Friends of Island Beach State Park asks for a $5 donation, according to Rosemary Mason, the group's president.
The plum festival is its major fund-raiser for the year and helps pay for a lot of what the group does, including printing 30,000 visitor guides; planting dune grass to help stabilize the shoreline; purchasing equipment; and operating an osprey camera that lets people around the world watch birds of prey in their nest as they hatch and feed their young.
Environmental and nonprofit groups will be at the festival to explain their missions, particularly protecting the fragile Barnegat Bay.
Hands-on activities include a surf-fishing clinic and seining, the process of catching fish and other marine life by dragging large nets on poles through shallow water.
Last year, there were virtually no plums to pick. The group is at a loss to explain why the crop failed in 2011, but planted additional bushes in new spots this year to help ensure robust harvests in future years.
The festival runs from 9 a.m. to 4 p.m.