Origin and Common Names:
Lobelia incisa Thunb. is a plant species that belongs to the Campanulaceae family. The plant is native to East Asia, particularly Japan, Korea, and China. The plant has several common names including Korean Lobelia, Japanese Lobelia, and Korean Bellflower.
General Appearance:
Lobelia incisa Thunb. typically grows up to 60 cm in height and forms a clump-like habit. The plant produces dark-green, glossy, lance-shaped leaves arranged alternately on the stem. The leaves grow up to 10 cm in length, and 4 cm in width, and have serrated edges. The plant produces spikes of showy, blue-violet, bell-shaped flowers during the summer months.
Uses:
Lobelia incisa Thunb. has several uses in traditional medicine and horticulture. In traditional medicine, the plant is used as an expectorant and to treat respiratory-related infections such as asthma, bronchitis, and cough. The plant contains alkaloids, lobeline, and lobelanidine, which are known to possess these medicinal properties. In horticulture, Lobelia incisa Thunb. is commonly used as an ornamental plant in landscapes, gardens, and as a container plant. The plant is prized for its striking blue-violet flowers, and it blooms consistently throughout the summer months.
Light Requirements
The Lobelia incisa Thunb. plant requires full sun to partial shade to grow properly. It thrives in bright sunlight but can also do well in shaded conditions. Too much shade can lead to stunted growth and reduced flowering. Therefore, it is recommended to grow the plant in a location that receives at least six hours of direct sunlight daily.
Temperature Requirements
The Lobelia incisa Thunb. plant is a hardy plant that can tolerate low temperatures. It can survive in temperatures as low as -15°C but thrives between 10°C and 25°C. In areas with harsh winters, it is essential to provide protection from freezing temperatures. In the summer months, the plant prefers cooler temperatures and will require frequent watering to prevent drying out.
Soil Requirements
The Lobelia incisa Thunb. plant grows best in well-drained soil with a slightly acidic pH of between 5.5 - 6.5. Avoid planting the plant in areas with heavy clay soils or in waterlogged soil as it can result in root rot and stunted growth. Prior to planting, it is recommended to prepare the soil by working in organic matter such as compost. Mulching the soil around the plant also helps to retain moisture and keep the roots cool during hot summer months.
Cultivation Methods
Lobelia incisa Thunb. is native to Japan and is usually grown as groundcover or border plant in gardens. It prefers well-drained soil and partial shade. The plant can be propagated through seeds or cuttings.
For seeds, sow them thinly in a seed tray and cover with a thin layer of soil. Keep the soil moderately moist and place the tray in a warm place with filtered sunlight. The seeds should germinate within 2-3 weeks.
For cuttings, take a stem cutting of about 4-6 inches long and remove the lower leaves. Dip the cut end in rooting hormone and plant it in a pot filled with a well-draining potting mix. Keep the soil moderately moist and place the pot in a warm and bright location with indirect sunlight. The cutting should root within 2-3 weeks.
Watering Needs
Lobelia incisa Thunb. prefers moderate watering. The soil should be moist but not waterlogged. Water the plant deeply once or twice every week, depending on the weather conditions. During summer, when the temperature is high, water the plant more frequently to keep the soil moist.
Avoid watering the plant from above, as it may cause the leaves to rot. Instead, water the plant at the base or use a drip irrigation system. Also, ensure that the soil drains well to prevent waterlogging.
Fertilization
Feed Lobelia incisa Thunb. with a balanced fertilizer once every month during the growing season. Choose a fertilizer with equal amounts of nitrogen, phosphorous, and potassium. Apply the fertilizer according to the manufacturer's instructions, and avoid over-fertilizing, as it may damage the plant.
You can also top-dress the soil with compost or well-rotted manure to provide the plant with nutrients. However, ensure that the soil drains well to prevent waterlogging, which may cause the roots to rot.
Pruning
Prune Lobelia incisa Thunb. regularly to keep it tidy and promote bushy growth. Remove any dead, damaged, or diseased leaves or stems as soon as you notice them. You can also pinch back the tips of the stems to encourage branching and increase the number of flowers.
After flowering, cut back the plant to a third of its height to promote new growth and ensure that the plant remains compact. Also, remove any spent flowers to prevent the plant from self-seeding and becoming invasive.
Propagation of Lobelia Incisa Thunb.
Lobelia Incisa Thunb. can be propagated through various methods like seed propagation, division, and softwood cutting.
Seed Propagation
This method involves sowing the seed of Lobelia Incisa Thunb. in a well-drained potting mixture at a depth of 2-3mm. The seeds are sown in spring or early summer. To ensure the germination of seeds, a temperature of 18-20 degrees Celsius is required. The seeds take almost 2-4 weeks to germinate. After that, the seedlings can be transplanted into bigger pots or directly in the garden when they have grown enough to survive.
Division
Division method involves dividing the mature clump of Lobelia Incisa Thunb. into 2-3 sections and planting them in new locations. This method is most successful in early spring when the plant is inactive. The plants should not be watered for almost a week after division, and the soil must be kept moist but not excessively wet.
Softwood Cutting
The softwood cutting method involves taking softwood cuttings in early summer and rooting them in a well-draining soil mixture. The cuttings approximately 5-8 cm in length should be planted in a mixture of compost and sand and placed in a shaded area. The soil should be moist but not excessively wet, and the cutting requires about two weeks for rooting. After roots have formed, the cutting can be transplanted to a larger container or planted in the garden.
Disease Management
Lobelia incisa Thunb. is susceptible to several diseases caused by fungal, bacterial, and viral pathogens, including:
- Botrytis blight: This fungal disease can cause stem rot and leaf spots. To manage this disease, remove the infected parts of the plant and avoid overhead watering.
- Leaf spot: Caused by several fungal pathogens, this disease causes yellowish-brown spots on the leaves. To manage this disease, remove the infected parts of the plant and improve air circulation.
- Crown rot: This fungal disease can cause rotting of the plant's crown, leading to wilting and stunted growth. To manage this disease, avoid overhead watering and improve soil drainage.
- Mosaic virus: This viral disease causes mottled yellowing of the leaves and stunted growth. Unfortunately, there is no cure for mosaic virus, so the best way to manage this disease is to remove and destroy infected plants.
Pest Management
Lobelia incisa Thunb. can also be affected by several pests, including:
- Spider mites: These pests are tiny and often go unnoticed until they have caused significant damage. To manage spider mites, regularly spray the plant with water to improve humidity and control their populations.
- Aphids: These pests are common on many plants and can cause distorted growth. To manage aphids, use insecticidal soap or neem oil spray to kill them on contact.
- Whiteflies: These pests are small and fly around the plant when disturbed. To manage whiteflies, introduce natural predators like ladybugs or hang yellow sticky traps to catch them.
- Slugs and snails: These pests can chew holes in the leaves and cause significant damage. To manage slugs and snails, handpick them from the plant or create a barrier around the plant with copper tape to prevent them from crawling up.
