Heat-loving Mexican petunia, or Ruellia brittoniana, is also called Florida bluebell, desert petunia, Mexican bluebell, wild petunia, garden ruellia and narrow leaf petunia. Violet-blue, white or pink flowers bloom summer and fall. Each lasts for only one day, but copious buds form continuously for extended blooming periods. Carefree and tender perennials hardy in USDA zones 7 to 9, ruellia die back from hard freezes. But unharmed roots bring them back in spring. Abundantly self-seeding, small colonies of Mexican petunias spread rapidly. Seeds easily germinated indoors by even beginners can be moved to sunny or partially shaded locations outside after frost.
Fill the cells of a seed-starting six-pack to a quarter inch from the top with seed-starting potting mix. Poke the tip of your finger lightly in the middle of each cell to make a small indent in the medium.
Drop several Mexican petunia seeds into each indent. Don't cover them with soil because they're very tiny.
Use a plastic spray bottle to carefully spritz the soil surface with warm water. The medium should be evenly moist but not soggy or waterlogged.
Seal the six-pack in a clear plastic bag, and poke some holes in it with a toothpick. This will ensure good air circulation within your mini-greenhouse nursery. Set the nursery in a warm, brightly lit location out of direct sun. The top of your refrigerator and a spot above a hot water heater are good choices.
Check the nursery daily to make sure that the soil remains moist. Seeds should germinate in three to five days. Move them to a sunny windowsill when they sprout. Continue to water enough to moisten the medium, and keep the plastic bag in place until the seedlings are about 1 inch tall.
Remove the plastic bag and keep the Mexican petunia seedlings moist. Transplant them outside when they're 2 to 3 inches tall and sustained temperatures remain above 50 degrees Fahrenheit.