So, what is the new black in floral fashion this summer? “The red mandevilla,” says Vincenzo Bomba, owner of Sun Valley Nursery (136 Croton Ave, Ossining, 914-762-6161). The Sol Parasols mandevilla, with its dark saturated-red blossoms, will climb trellises, fences—any place sunny—all summer, up until the first frost. Bomba notes they range in price from $28 to $100, depending on size.