- Lobelia seeds require temperatures above 65 degrees F for germination and can be started indoors, in spring, in areas colder than this. Bury seeds in a few inches of soil in a seed tray or grow pots, water in well and place the pots in a warm, sunny location kept between 65 and 75 degrees F. As outdoor temperatures get above 60 degrees F, you can begin to harden off the seedlings gradually before planting. To harden off the plants, place them outdoors for increasingly longer periods of time, beginning with a few hours per day. Transplant them outdoors after last frost has well passed. For direct outdoor seed sowing in warmer climes, select a sunny area with well-drained soil, amended with compost or well-aged manure. Space the seeds a few inches apart, covering with 1/2 inch or so of soil, and water in well.
- Lobelia thrives in a full sun to partial shade exposure and likes a well-drained, slightly acidic or neutral soil pH between 6.5 and 7.5. If you have alkaline soil, amend it to boost the acidity by tilling in some sphagnum peat moss or gypsum. Lobelia roots should be kept evenly moist, but never allowed to sit in water. Water lobelia at the roots and around the drip line, never over the foliage to prevent rust and leaf spot. Feed with a water-soluble, balanced fertilizer beginning in spring at two to three week intervals until bloom. Dose according to the product instructions. If you go to the trouble of deadheading spent lobelia blooms, it will encourage flowering. Using small shears or scissors will make an easier job of deadheading the small flowers.
