Lobelia: Indoor Sow Annual
How to Sow and Plant
Lobelia may be grown from seed sown early indoors and transplanted outside after frost
Sowing Seed Indoors:
- Sow lobelia indoors 8-12 weeks before the last frost using a seed starting kit.
- Sow thinly and just press into planting formula.
- Keep soil moist.
- Seedlings emerge in about 20 days at 65-75 degrees F.
- As soon as seedlings emerge, provide plenty of light on a sunny windowsill or grow seedlings 3-4 inches beneath fluorescent plant lights turned on 16 hours per day, off for 8 hours at night. Raise the lights as the plants grow taller. Incandescent bulbs will not work for this process because they will get too hot. Most plants require a dark period to grow, do not leave lights on for 24 hours.
- Seedlings do not need much fertilizer, feed when they are 3-4 weeks old using a starter solution (half strength of a complete indoor houseplant food) according to manufacturer’s directions.
- If you are growing in small cells, you may need to transplant the seedlings to 3 or 4 inch pots when seedlings have at least 2 pairs of true leaves before transplanting to the garden so they have enough room to develop strong roots
- Before planting in the garden, seedling plants need to be “hardened off”. Accustom young plants to outdoor conditions by moving them to a sheltered place outside for a week. Be sure to protect them from wind and hot sun at first. If frost threatens at night, cover or bring containers indoors, then take them out again in the morning. This hardening off process toughens the plant’s cell structure and reduces transplant shock and scalding.
Transplanting in the Garden:
- Select a location in full sun with good rich moist organic, well-draining soil. In areas with hot summers, choose a location with afternoon shade.
- Prepare the bed by turning the soil under to a depth of 8 inches. Level with a rake to remove clumps of grass and stones.
- Most plants respond well to soils amended with organic matter. Compost is a wonderful form of organic matter with a good balance of nutrients and an ideal pH level, it can be added to your planting area at any time. If compost is not available, top dress the soil after planting with 1-2 inches of organic mulch, which will begin to breakdown into compost. After the growing season, a soil test will indicate what soil amendments are needed for the following season.
- Space plants 6 inches apart in the garden.
- Water after planting.
How to Grow
- Keep weeds under control during the growing season. Weeds compete with plants for water, space and nutrients, so control them by either cultivating often or use a mulch to prevent their seeds from germinating.
- Mulches also help retain soil moisture and maintain even soil temperatures. For annuals an organic mulch of shredded leaves lends a natural look to the bed and will improve the soil as it breaks down in time. Always keep mulches off a plant’s stems to prevent possible rot.
- Keep plants well-watered during the growing season, especially during dry spells. Plants need about 1 inch of rain per week during the growing season. Use a rain gauge to check to see if you need to add water. It's best to water with a drip or trickle system that delivers water at low pressure at the soil level. If you water with overhead sprinklers, water early in the day so the foliage has time to dry off before evening, to minimize disease problems. Keep the soil moist but not saturated.
- Until plants become established, some protection from extreme winds and direct, hot sunlight may be necessary. Good air movement is also important.
- After new growth appears, a light fertilizer may be applied. Keep granular fertilizers away from the plant crown and foliage to avoid burn injury. Use low rates of a slow release fertilizer as higher rates may encourage root rots.
- Shear plants back after the first flush of bloom to encourage reblooming.
Growing Tips
- Annual lobelia grows best in cool areas or where nighttime temperatures are cool.
- Ideal for hanging baskets and window boxes due to its trailing habit.
- Good annual groundcover, or for rock gardens and as edgings.
- Plants are not heat tolerant but tend to revive in late summer when temperatures begin to cool off.
Common Disease Problems
Bacterial Leaf Spot: First signs are small translucent spots with a broad yellowish edge that slowly enlarge and become angular or irregularly circular with a reddish center. It thrives in cooler temperatures. The disease may also affect and disfigure flower heads. Burpee Recommends: Remove infected plants. Rotate crops with plants in a different family. Avoid overhead watering. Do not work around plants when they are wet.
Botrytis: This fungus causes a grey mold on flowers, leaves, stems and buds. It thrives in cool wet weather conditions. Burpee Recommends: Remove affected plant parts, avoid watering at night and getting water on the plant when watering. Make sure plants have good air circulation. Contact your Cooperative Extension Service for fungicide recommendations
Root Rots: A number of pathogens cause root rots of seedlings as well as mature roots. Burpee Recommends: Practice crop rotation and do not plant related crops in the same area for several years. Pull up and discard infected plants. Make sure your soil has excellent drainage. Contact your Cooperative Extension Service for recommendations.
Rust: A number of fungus diseases that cause rust colored spots on foliage. Burpee Recommends: Practice crop rotation. Remove infected plants. Contact your Cooperative Extension Service for recommendations.
Common Pest and Cultural Problems
Aphids: Greenish, red, black or peach colored sucking insects can spread disease as they feed on the undersides of leaves. They leave a sticky residue on foliage that attracts ants. Burpee Recommends: Introduce or attract natural predators into your garden such as lady beetles and wasps which feed on aphids. You can also wash them off with a strong spray, or use an insecticidal soap.
Corn Earworm: Worms tunnel into stems causing the stems to collapse as they cannot take up water and nutrients from the soil. Burpee Recommends: This is difficult to control once the larvae are in the stems, but removing affected clumps can prevent the spread to healthy plant stems. Contact your Cooperative Extension Service for recommendations.
Slugs: These pests leave large holes in the foliage or eat leaves entirely. They leave a slime trail, feed at night and are mostly a problem in damp weather. Burpee Recommends: Hand pick, at night if possible. You can try attracting the slugs to traps either using cornmeal or beer. For a beer trap, dig a hole in the ground and place a large cup or bowl into the hole; use something that has steep sides so that the slugs can’t crawl back out when they’re finished. Fill the bowl about ¾ of the way full with beer, and let it sit overnight. In the morning, the bowl should be full of drowned slugs that can be dumped out for the birds to eat. For a cornmeal trap, put a tablespoon or two of cornmeal in a jar and put it on its side near the plants. Slugs are attracted to the scent but they cannot digest it and it will kill them. You can also try placing a barrier around your plants of diatomaceous earth or even coffee grounds. They cannot crawl over these.
Spider Mites: These tiny spider-like pests are about the size of a grain of pepper. They may be red, black, brown or yellow. They suck on the plant juices removing chlorophyll and injecting toxins which cause white dots on the foliage. There is often webbing visible on the plant. They cause the foliage to turn yellow and become dry and stippled. They multiply quickly and thrive in dry conditions. Burpee Recommends: Spider mites may be controlled with a forceful spray every other day. Try hot pepper wax or insecticidal soap. Check with your Cooperative Extension Service for miticide recommendations.
Thrips: Thrips are tiny needle-thin insects that are black or straw colored. They suck the juices of plants and attack flower petals, leaves and stems. The plant will have a stippling, discolored flecking or silvering of the leaf surface. Thrips can spread many diseases from plant to plant. Burpee Recommends: Many thrips may be repelled by sheets of aluminum foil spread between rows of plants. Remove weeds from the bed and remove debris from the bed after frost. Check with your Cooperative Extension Service for pest controls.
Lobelia FAQs
Why did my lobelia turn brown over the summer? Is it dead? Lobelia can brown out when temperatures are hot and it has been underwatered. The plant tissues may die in these conditions. Watering can sometimes stimulate new growth. Try to bring plants into a shadier location, or out of the afternoon sun, if they are in a container. Be sure to not let the plants dry out. Many times lobelia will revive when temperatures are cooler at the end of the summer.
Are lobelias good for attracting pollinators? Yes, they attract bees, butterflies and hummingbirds.
Can I grow lobelias in a container? Yes, they are perfect for containers!
Are lobelias toxic? Yes, the plants are toxic if eaten.