Dwarf Mexican Petunia/Katie Dwarf Ruellia Dwarf Mexican petunias are perennial and have dark green, lance-shaped leaves that will remain green until they get a hard frost. They will then go dormant until spring. In the summer, ruellia will be in full bloom through the hottest days. They love full sun and dry conditions. 'Katie' dwarf ruellia comes in pink, purple and white. This 'Texas Superstar' stays very short (6 inches tall) and can be used as a border or ground cover.