Members of the Lobelia can be either half hardy annuals or perennials.
The height and flower type varies upon the variety, with perennials reaching about 90 cm, and having minute blue or yellow flowers on terminal spikes; annual Lobelia are low growing (10 to 30 cm) and have massed blooms of purple, blue, or white flowers.
The annuals are ideal for growing in rock gardens and as edging plants, whereas perennial Lobelia are of use in borders.
Some of the common names for Lobelia are cardinal flower and Edging Lobelia.
Lobelia spicata - Pale Spiked Lobelia by Gmayfield10.
Common Names: Lobelia, Indian Tobacco, Pukeweed, Asthma Weed, Vomitweed, Cardinal flower. Lobelia: Edging; Trailing; Annual; Heath.
Life Cycle: Half hardy annual. Half hardy perennial.
Height: Annuals: 3 to 14 inches (7 to 35 cm). Perennials: 24 to 48 inches (60 to 120 cm).
Native: Worldwide except Central and Near Eastern Asia.
Growing Region: Annual: zones 1 to 10. Perennial: zones 2 to 10.
Flower Details: Red, blue, purple, white. Asymmetric. Five lobes. Tubes. Often in racemes.
Foliage: Simple. Alternate. Lanceolate; Oval.
Sow Outside: Start indoors.
Sow Inside: Surface. Use vermiculite. Water from below. Prepare perennials by first mixing seeds in the vermiculite, placing in a freezer bag, keep moist, then stratify by refrigeration for three months. Germination time: two to three weeks. Temperature 70 to 75°F (21 to 24°C). Eight or nine weeks before expected last frost. Transplant outdoors a few weeks after the last frost; temperatures should not fall below 41°F (5°C). Spacing: annuals: 4 to 6 inches (10 to 15 cm); perennials: 10 to 24 inches (25 to 60 cm).
Requirements: Full sunlight or partial shade. Good drainage. Soil pH 6 to 7.5. Hummus rich soil. Moist soil. Regular watering to keep the soil moist. Deadhead. Propagate: divide or take cuttings in autumn (warm areas) or spring (cooler areas).
If growing Lobelia plant from seeds it is best to start them off indoors.
The seeds of annuals should be sown on the surface of vermiculite about seven weeks before due to be transplanted, a few weeks after the last frost of spring, they should be watered from below.
The perennial seeds should be prepared about 14 weeks in advance. First the seeds should be imbibed by placing the seeds (within soil) in a black bag, then placing in the fridge for three months.
Seeds should then be sown out in vermiculite at a temperature of 18 to 24 degrees.
It should take about 3 weeks to germinate. Once growing they are susceptible to rotting so water from below.
The Lobelia seedlings should be transplanted with a spacing of 10cm (small Lobelia varieties) to 60 cm (large Lobelia species) apart.
Lobelia can grow in either a sunny or partially shaded part of the garden and prefer a moist humus rich soil that has a pH of between 6 and 7.5
Once established in the garden Lobelia require a little bit of looking after; they should be watered regularly to keep the soil moist in dry spells.
It is best to remove the dead heads of Lobelia flowers when growing.
If you require more perennial Lobelia plants then you can take divisions or cuttings of the plants in spring or summer.