Starting annuals from seed is a cost effective way to repopulate the garden with colorful flowers each spring. Lobelia is easy to grow and well-suited for borders, edging and as bedding plants. One of the best tips for starting lobelia seeds is to sow the seeds indoors in winter. By the time spring comes around and the ground thaws out, the plants will already be growing vigorously, ready to add color to the garden. A low-effort alternative is to simply scatter the seeds over the soil in the garden once the weather warms up and let the seeds come up on their own.
Lobelia seeds can be started indoors or in a greenhouse 12 to 13 weeks before the last frost date. Starting seeds early is the most cost effective way to have a supply of annual plants to transplant into the garden in spring. Nurseries and markets sell annual seedlings in spring, but they cost a lot more than a packet of seeds and some potting soil.
One of the best tips for starting lobelia seeds indoors is to use a seed-starting flat or cell packs and quality seed-starting mix. Seed-flats are commonly at least 2 inches (about 5 cm) deep and rectangular. Cell packs come in groups of two, four, six or eight. They have individual compartments that are 1 inch (about 2.5 cm) deep and 1 inch (2.5 cm) wide.
Commercial seed-starting mix is formulated to be light weight, sterile and to hold moisture. A sterile environment is important for starting lobelia seeds. Regular garden soil is heavy and can smother the the seeds, causing them to rot before they can germinate. One of the best tips is to mix the seed-starting mix with water before filling the seed-flat or cell packs. The mix should be crumbly and damp without being saturated or muddy.
After filling the seed flat or cell pack, the lobelia seeds should be placed on top of the soil. A thin layer of the damp seed mix should be spread over the top of the seeds. Lobelia seeds require light in order to germinate. Burying them too deep will result in poor or no germination.
Consistent temperature is important when germinating seeds indoors. The optimum temperature for lobelia seeds is 75°F (about 23°C). It is important to keep the soil evenly damp throughout germination and early growth. Seeds and developing seedlings can dry out quickly and perish without enough moisture. Lobelia seeds germinate in about 21 days.
Lobelia seedlings can be planted outdoors in spring after the last frost date. A spacing of 6 inches (about 15 cm) creates a dense planting while giving each lobelia space go grow and develop. New transplants should be kept consistently damp for the first few weeks until they get established.
To save time and effort, lobelia seeds can be sown directly into the garden bed after the last frost date. The garden bed should be cleared and raked flat, then amended with compost or manure to improve soil texture and nutrition. The seeds can be scattered onto the soil and raked in. It is a good idea to over seed when planting directly out, as germination rates are lower than greenhouse-started lobelia seeds.