Answer: If your lisianthus seeds are sprouting, then dying, the seeds are viable, they're just not getting what they need to thrive. Be sure to remove the plastic as soon as seeds sprout to provide good air circulation. Otherwise your seedlings can develop the fungal disease called damping-off.
Plants should be fertilized when they've developed their second set of leaves, and new seedlings should be given 12-14 hours of light each day. You'll have to supplement natural light with artificial light at this time of year to provide enough light. Use one cool and one warm light fluorescent bulb in a shoplight fixture, hanging it so the bulbs are only 2"-4" above the tops of the plants. Keep the light on at least 12 hours each day and turn them off at night.
Water should be applied often enough to keep the soil from drying out, but not so often that the soil stays soggy wet.
Try following the above guidelines and your next batch of lisianthus seeds should produce healthy seedlings.
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