Trailing lobelia (Lobelia erinus) is a popular annual flowering plant known for its abundant small blooms and cascading growth. It adds continuous color and a softening effect to garden edges and containers, making it an excellent choice for borders.
Why Trailing Lobelia Excels in Borders
Trailing lobelia’s prolific flowering habit provides continuous color from spring until the first frost. The plant produces numerous small, two-lipped tubular flowers, typically 0.5 to 1 inch long.
These delicate blooms come in various shades of blue, purple, white, and pink, sometimes with contrasting throats. Trailing lobelia (Lobelia erinus var. pendula) naturally develops a spreading or cascading form, reaching 6 to 12 inches wide and 6 to 9 inches high. This growth habit allows it to spill over the edges of garden beds, pathways, or raised borders, softening lines and providing a continuous groundcover effect.
Planting Trailing Lobelia for Border Success
Proper site selection is crucial for establishing trailing lobelia in a border. The plant thrives in full sun to partial shade, needing at least 4-6 hours of direct sunlight daily. In hot climates, afternoon shade can prevent decline and encourage continued blooming.
Trailing lobelia performs best in well-draining soil rich in organic matter. An ideal soil pH is slightly acidic, between 6.0 and 7.0. Amend existing border soil with organic compost to enhance nutrient content and drainage.
When planting, space lobelia 6 to 18 inches apart, depending on variety and desired coverage. Gently remove plants from nursery containers, teasing out any pot-bound roots. Plant them at the same depth as their original container, ensuring the base is level with the surrounding soil.
After placing, backfill holes with soil and lightly tamp to remove air pockets. Immediately water thoroughly to settle the soil around the roots and aid establishment.
Essential Care for Thriving Border Lobelia
Once established, consistent watering is essential for trailing lobelia, as it is not drought-tolerant. Keep the soil evenly moist but not waterlogged to prevent root rot. During dry or hot periods, increase watering frequency; check the top 1-2 inches of soil and water when dry.
Regular fertilization supports continuous blooming. Apply a balanced liquid fertilizer every two to three weeks during the growing season. Fertilizers with an NPK ratio like 5:7:7, 7:8:6, or a balanced 20-20-20 are beneficial, with higher phosphorus promoting more flowers. Mix and apply according to product instructions, avoiding foliage.
While many annual lobelias are self-cleaning, light shearing or deadheading encourages new growth and prolongs flowering. If plants become leggy or flowering wanes, trimming them back by up to a third can rejuvenate them. Trailing lobelia generally resists pests and diseases, though aphids, spider mites, or root rot can occur. Proper air circulation and avoiding overwatering are key to preventing these issues.
Maximizing Your Border Display
To maximize the visual impact of trailing lobelia, place it strategically. Its cascading habit makes it ideal for planting at the front edge of a border, spilling gracefully over low walls, rocks, or the perimeter. This creates a soft, flowing transition to adjacent hardscapes.
Trailing lobelia pairs well with companion plants sharing similar light and moisture preferences. Cool-season plants like pansies, violas, and sweet alyssum complement its colors and form. Other suitable companions include petunias, fuchsias, impatiens, ferns, and hostas (in appropriate light).