Lobelia prefers coolness and some shade, making it a good choice for areas in the garden other plant don't thrive in. There are both annual and perennial varieties of lobelia available. It works well in beds and borders, or planted in hanging baskets so the tendrils of small flowers can overhang the edges. They bloom from early summer until the first fall frost, though growth and blooming slows during the heat of summer. Lobelia requires minimal maintenance and care to thrive throughout the summer and fall.
Place perennial lobelia seeds between two moist paper towels. Place inside a plastic bag and seal. Refrigerate for two months prior to planting in spring. Cold stratification is necessary in order for the seeds to break dormancy.
Start lobelia seeds indoors three months before the last expected spring frost in your area. Check a USDA gardening zone map to find your last frost date (see Resources).
Fill seed starting trays with a quality soil mix. Alternately, mix your own by combining 1 part vermiculite, 1 part peat moss and 1 part sterilized compost.
Sow lobelia seeds directly on the soil surface in rows 3 inches apart. Lobelia seeds are very small so sow as thinly as posible. Cover with a 1/8 inch layer of soil or vermiculite.
Moisten the surface of the soil by misting with a spray bottle. Cover trays with plastic wrap to preserve moisture and place in a 65 to 75 F room to germinate.
Remove plastic wrap once seeds germinate, approximately 14 to 21 days after sowing. Move to a well-lit window or place under grow lights and keep the soil moist at all times.
Transplant lobelia to a well draining garden bed in partial shade or transplant into permanent containers after all danger of frost has passed in your area.