Lisianthus can be a challenge
to start from seed because it’s very sensitive to temperatures over
75 degrees. Be careful to keep temperatures below this throughout the process
or it will cause rosetting, or a resting stage. These resting stages can
last for weeks or even months, making it hard to get young plants large
enough to set out in your garden by spring. 
Sow seeds in early winter (mid-December to January,
or 16 to 22 weeks before your average last frost date). Because lisianthus
seed is so fine, you’ll usually find it already pelleted. Saturate
a good-quality, fine peat and vermiculite-type potting medium and spread
the seed on top. Cover the container with a plastic dome or a plastic
wrap secured with a rubber band to hold in the moisture. Place fluorescent
or grow lights ½ to 1 inch above the cover on your container. The
seeds should receive 16 hours of light per day until the seedlings start
to emerge, in about 2 weeks. During this time keep the temperature constant
— 70 to 75 degrees.
Remove the dome or plastic once the seedlings start
to emerge, and adjust the lights so they’re 1½ to 2 inches
above the top of the plants. Nighttime temperatures can be cooler now
— 60 to 65 degrees. But don’t let them drop much below 60
degrees. Water the growing medium from the bottom now and keep it moist
to the touch, not saturated. Provide good ventilation. You may start feeding
with a calcium-based fertilizer (13-2-13) at half strength once a week
now. At the end of this stage, roots and the first leaves, or cotyledons,
have developed.
Transplant the seedlings into 4-packs after 7 to 8 weeks,
when the seedlings have developed 2 or 3 sets of true leaves. At this
stage, the seedlings are not as prone to rosetting, so it’s not
as critical to keep temperatures below 75 degrees. As you move them, grasp
a leaf and use a small spoon to scoop out as much of the medium with the
roots as possible, as the roots are very sensitive. Plant the seedlings
so that the bottom leaves are just above the mix. Continue to bottom water
the containers, but increase the feeding to half-strength every watering.
Let the medium dry out a little between watering now.
Move the young plants out to the garden when they are
3 to 4 inches high and have 3 to 4 sets of true leaves (usually around
the end of May or beginning of June). Place them outside for gradually
longer periods of time to harden them for a couple of weeks first. Then
plant them in moist, well-drained soil where they will get at least 6
hours of sun a day. The plants bloom from July to frost if you keep them
deadheaded.
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