Edging lobelia (Lobelia erinus) is a native South African flowering plant related to the bellflower. Edging lobelia is a popular garden plant for ornamental purposes and is often cultivated in hanging baskets and planters. Edging lobelia can be damaged by frost and cold temperatures and grows best in temperate climates.
I. Appearance and Characteristics
Lobelia erinus (edging lobelia, garden lobelia or trailing lobelia) is a species of flowering plant in the bellflower family Campanulaceae, native to southern Africa.
It is a low growing, prostrate or scrambling herbaceous perennial plant growing to 8–15 cm tall. The basal leaves are oval, 10 mm long and 4–8 mm broad, with a toothed margin; leaves higher on the stems are slender and sometimes untoothed.
The flowers are blue to violet in wild plants, with a five-lobed corolla 8–20 mm across; they are produced in loose panicles. About 0.5 to 4.5 inches long inflorescence stems are about 5 inches long, loose racemose inflorescences with many flowers. The hermaphrodite flower is zygomorphic with a length of up to 1 centimeter and quinate with double perianth. The five sepals are fused. The fan-shaped lower lip is trilobed. The color of the crown varies depending on the variety between white, blue, purple, pink or red and the center is yellow or white. The five stamens are 3 to 7 millimeters long.
The fruit is a 5–8 mm capsule containing numerous small seeds.
II. How to Grow and Care
Sunlight
For the most part, lobelia isn’t too picky about sunlight and can thrive in partial shade to full sun locations. However, if your summers tend to be very hot, it is best to plant lobelia where it will receive direct sun only in the morning and part-shade to shade in the afternoon. In areas with milder summers, grow it in full sun (as long as you water it regularly) to enjoy maximum flowering.
Temperature and Humidity
Annual lobelia does best in moderate temperatures and with moderate humidity. However, it can thrive even outside those conditions as long as you provide a little extra care. In hot climates, planting lobelia where it will be protected from the peak afternoon sun can help prevent scorch or plant death. Regular watering will help maintain enough humidity for the plant to do well, but in very dry conditions, the leaves might shrivel. If you take quick action with the hose or watering can, often the plant will revive. Annual lobelia will not survive freezing temperatures and is generally discarded in the winter.
Watering
Always keep the Trailing Lobelia uniformly moist. Especially when growing in pots, the substrate should never dry out completely. To prevent waterlogging we recommend adding a made of expanded clay or similar, at the bottom of the planting container.
Soil
Lobelia likes rich, well-drained soil. Don’t let conditions get soggy, however, which can cause root rot.
Fertilizing
Since lobelia is a prolific bloomer and heavy feeder, you’ll get the best results by fertilizing it every two weeks with a liquid fertilizer formulated for flowering plants. These typically are somewhat higher in phosphorus than in nitrogen and potassium, as phosphorus promotes more flowers.
Mix the fertilizer with water in a watering can according to package directions, and apply it to the base of the plant, avoiding its leaves. Continue to fertilize your lobelia regularly through the summer to keep it flowering.
Propagation
Like most annual flowers, it’s easy and economical to grow lobelia from seed. You will have more success with seeds than propagating lobelia in other ways. You’ll also often have a better choice of varieties when planting from seed, rather than from nursery plants.
In cold-winter climates, it’s recommended to start lobelia seeds indoors 6 to 8 weeks before the average last frost date for your area. In mild-winter areas, you can sow the seeds outdoors in the early spring, as long as nighttime temperatures are reliably more than 50 degrees Fahrenheit. Take these steps:
- Scatter the very tiny seeds evenly atop a seedling tray filled with seed-starting soil. Do not bury the seeds, however.
- Set the uncovered tray near a window that provides good light.
- Mist the tray with water to moisten the soil.
- Continue to mist the soil daily, or as often as required to keep it moist, not soggy. The seeds should begin to germinate two to three weeks after sowing.
- Once nighttime temperatures are regularly over 50 degrees Fahrenheit, it’s time to plant your lobelia in the garden. First, harden off the plants gradually to allow them to adjust to outdoor conditions. Then, gently separate the seedlings, taking care not to tear their roots, and plant them in your desired location outdoors, whether in the ground or a container.
- Space your annual lobelia plants 4 to 6 inches apart in containers and slightly further apart if planting directly into the ground.
Potting and Repotting
Lobelia is typically used to edge the front of a flower border, but it is also heavily used in a container garden or can be seen spilling over the sides of a hanging basket. Lobelia prefers moisture, especially in hot weather, but it does not like to be soggy. Any container should have plenty of drainage holes. Consider plastic containers to retain moisture but if you choose ceramic pots, just remember to check when to water the plant since it will dry out faster. If planting lobelia in a container or hanging basket, a good potting soil will keep this plant blooming all season long.
Overwintering
Wintering is only possible in very few Trailing Lobelia varieties. The ‘Richardii’ variety, for example, can be placed in bright winter quarters between 50 and 59 degrees Fahrenheit before the first frosts. When placed there, water it moderately and put it back outside after ice saints. As a rule, however, it makes more sense to collect the seeds in fall and sow the lobelia again next spring.
Pests and Diseases
Common Pests
The main pest that can damage lobelia is the spider mite. A minor spider mite infestation can be handled with gentle sprays of cold water. A severe infestation may require insecticidal soap, neem oil, or pesticides as a last resort. Corn earworms also like lobelia, and they eat holes in leaves which can make the plant vulnerable to developing fungal diseases. Manual removal and insecticides can help eliminate the corn earworms before too much damage is done.
Common Problems
This delicate plant can have its share of problems thanks to interesting pests and its light sensitivities. Here are a few signs to look for:
Browning Foliage
Overwatering is a common issue with lobelia. Since it doesn’t like hot weather, you may tend to overwater and as a result, the leaves will brown. On the other hand, lobelia turns brown if it’s overheated. Try moving the container to shade or add temporary shade if lobelia is planted in the ground but drying up under the sun.
Leaves Curling
Along with extreme heat, lobelia also can’t handle very dry conditions. If the plant is feeling any sort of drought conditions, the leaves may brown and start to curl up around the edges to protect themselves. Do as you would with browning foliage and give the plant more shade and watering.
Spotted Leaves
Mites may be attacking the plant by sucking out the juices from its leaves, turning them spotty. As soon as you see some spots, use insecticidal soap to remedy the situation.
Brown Base
If the foliage isn’t browning, but it appears as though the base of the mound is turning brown, you could have corn earworms, which is another type of insect infestation. This can be tough to treat if the damage is already done (holes in leaves). The damage can make the plant susceptible to fungi diseases so it’s best to remove damaged sections immediately so the problem does not spread.
III. Uses and Benefits
Most often you can find the Trailing Lobelia in the balcony or terrace. Tried and tested companion plants are nasturtiums or pelargoniums (geraniums). Tone-on-tone plants with, for example, blue daisies ensure a continuous sea of flowers. In the garden, lobelia are often used as ground cover, for bed borders or sunny flower beds.
Find Where to Buy the Best Lobelia (Lobelia erinus)
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