Technically a tender perennial, many modern petunia hybrids are now grown as annuals in all USDA Plant Hardiness Zones. Their voluminous flowers also make petunias ideal for outdoor hanging baskets, but know that some varieties do require a bit of trimming and deadheading. For a low-maintenance, heat-tolerant variety that doesn't need deadheading, try 'Supertunia Vista'. "It can trail up to 4 feet in a container!" says Melissa Lallo Johnson of @fancyflowerfarmer, a master gardener based in the Midwest.