Lobelia erinus is commonly grown in window boxes or around the edges of gardens as an edging plant.
It’s got thin basal leaves and deep blue, purple, or white flowers.
The plant is native to South Africa and was first cultivated in the 1600s.
It’s become a popular choice for gardens around the world, resulting in hundreds of hybrids.
Lobelia erinus, pronounced [low-BEE-lee-a EAR-rin-us], belongs to the family Campanulaceae. The plant has a few common names, including:
- Edging lobelia
- Garden lobelia
- Trailing lobelia
There are also two main varieties — a long, trailing plant and a shorter, compact variety.
No matter which is grown, it’s an easy plant to care for and produces a mass of small colorful flowers.
Relatives include the old fashion bellflower Campanula plant and Isotoma axillaris the star flower.
Lobelia Erinus Care
Size and Growth
The edging lobelia is the shorter of the two main types.
It rarely grows more than 6″ inches high while the trailing habit lobelia can produce leggy growth up to 12″ inches.
Lobelia has thin leaves and delicate stems but may spread a couple of feet, making it great for edging borders.
Flowering and Fragrance
The plant blooms in the summer, producing hundreds of little white, pink, purple, violet or blue flowers with white eyes.
There are also many hybrids offering various shades and flower colors.
Bloom time runs from early summer until mid-fall.
Light and Temperature
The garden lobelia needs full sun or partial shade and mild temperatures.
It’s winter hardy to USDA hardiness zones 10 and 11 but it’s mostly grown as an annual in the cooler regions.
If protected against freezing temperatures, it can be grown as a perennial, continuing to grow the following summer.
Watering and Feeding
The plant should receive regular watering and feeding throughout the summer to help produce fuller blooms.
If it’s planted in the garden, water the plant twice per week and feed every two weeks. For container plants, water every during the warmer months.
In the winter, don’t feed and limit watering.
Soil and Transplanting
Garden lobelia grows best in rich soil that offers fast drainage. If grown as an annual, the plant doesn’t need transplanting.
When keeping the plant over winter, add fresh soil or transplant in the spring.
Grooming & Maintenance
If the plant is kept outdoors during extremely warm weather, it may stop flowering. When this occurs, trim back the stems and give the plant a thorough watering.
How to Propagate Lobelia Erinus
The plant may be propagated with cuttings or seeds. As it’s typically grown as an annual, collecting the seeds is the easiest way to keep the plant year after year.
Sow the seeds at room temperature or about 70 degrees Fahrenheit. It should take close to two weeks for the seeds to germinate.
NOTE: The seeds will germinate at lower temperatures but it takes much longer.
Use small pots or starter trays to sow the seeds on top of propagating soil. Sow in early spring and wait about one month before thinning seedling out into different pots.
When repotting, use rich, well-drained soil. Leave the plants in place until the end of spring when they can be transplanted into outdoor containers or gardens.
Propagating with cuttings requires planning. In the early fall, move the mother plant to a cool area of the house or yard. It should be below 70 degrees Fahrenheit most of the day.
Ensure that the plant gets plenty of light but limit the watering until February. Move the plant to a warmer spot and wait for the growth to start.
When the plant starts actively growing, trim a few stems and plant them in sandy soil or pure sand.
Keep the young plants in bright light and avoid overwatering. After they take root, transplant them into rich soil, the same as the soil used for the mother plant.
The new plants should flower around the start of the summer.
Erinus Lobelia Pests or Diseases
Lobelia erinus plants are toxic. The toxins in the leaves, stems, and flowers may be harmful to pets and humans.
Cats and dogs especially should be kept away from the plant.
Besides keeping pets and children away from the plant, a lack of water and spider mites are the main issues to worry about.
As mentioned, Lobelia plants may stop flowering in the summer.
This is often due to dry conditions from excessive heat but it can also be caused by underwatering. Cut the plant back and give it plenty of water.
Eggs and larvae are signs of red spider mite infestations.
The leaves of annual Lobelia may also start to turn brown or bronze before falling off as the mites take nutrition from the plant.
Mist the plant with cold water to help prevent attacks or stop minor infestations. If the problem gets severe, try using insecticide.
Suggested Uses For Blue Lobelia
The trailing Lobelia erinus variety looks great growing in hanging baskets or window box.
The edging variety works well for edging around garden beds or tubs, massed as a ground cover, used in rock gardens or bring color to a small balcony.
With either variety, consider planting taller plants behind the lobelia for a fuller look.