Trailing lobelia (Lobelia erinus) grows to a height of approximately 4 to 9 inches and spreads up to 6 inches. It grows best in moist soil. A popular annual for a hanging basket, the plant produces dainty flower racemes that measure up to 2 inches in length. Flowers appear in shades of blue, pink, white, purple and red. Available in a compact bush form or as a trailing plant, many cultivars exist. The plant adapts easily to containers. The trailing variety is often referred to as Lobelia erinus pendula, according to the University of Michigan.
Place any hanging basket that contains trailing lobelia in full sunlight for the best growth. In areas with exceptionally hot summers, the plant will benefit from partial shade in the afternoon.
Water the hanging lobelia basket often to keep the soil moist but not waterlogged. Apply the water to the top of the basket until it runs freely out the bottom and sides of the container. During the height of summer, the hanging basket may require daily watering to keep the soil moist.
Fertilise the hanging lobelia every other week using a general-purpose water-soluble fertiliser. Follow the directions on the label to mix the fertiliser into the water and apply.
Remove the spent blossoms of the lobelia as they appear by pinching or clipping them away. If the plant is allowed to produce seed after blossoming, it will gradually cease to flower because it is an annual plant and completes its life cycle in one season. Once seed production begins, the plant no longer produces flowers. Removing the spent flowers prior to seeds appearing will encourage the plant to continue to flower throughout the summer and into the fall.
Consider starting lobelia seeds indoors 10 weeks prior to the last expected frost. Plant trailing lobelia along the edge of the hanging basket so it cascades over the sides. Plant compact lobelia in the middle of the basket to form a dense mound. Applying a 2-inch layer of sphagnum moss around the lobelia plants will help keep the soil moist during the hot summer months.
Avoid fertilising the plants within the hanging basket with fertilisers high in nitrogen or the plant will produce abundant foliage and few flowers, according to Iowa State University.