Lobelia plants (Lobelia erinus) are hardy annuals that enjoy shade, moisture and fertile soils. Lobelias bloom profusely with tubular flowers that range in color from white to purple or deep-blue, depending on the cultivated variety. These plants grow only 6 to 12 inches tall and wide, some of which are trailing varieties and others mounding. Lobelias will bloom right up until the first frost in fall and can be grown in the ground outdoors or in containers. Lobelias are often planted in flower beds, borders or hanging baskets.
Water your lobelia plants thoroughly once or twice each week to keep the soil moist to wet. Water the lobelias daily during dry spells or droughts.
Feed your lobelias once each month with a water-soluble or liquid all-purpose flower fertilizer. Follow the application directions on the package.
Shear back the lobelia plant's stems after the first blooming is finished to encourage a healthy subsequent blooming. You don't need to deadhead the flowers when they fade, because the spent blooms will fall off the lobelia plant naturally.
Bring container-grown lobelias indoors before the first frost in fall, if you want to keep the plants blooming into early winter. Keep the lobelias in a sunny, humid room during the winter, and then place it back outside after the last frost in spring.