You do not have to wait until the seeds sprout to use Osmocote. It is slow release so you can work it into the soil at planting time or if you forget, sprinkle the Osmocote into soil later. Lettuce is not a heavy feeder so I would use one tablespoon of Osmocote for a 30 inch planter. Remember that lettuce is a leaf crop and likes to have cool roots. A mulch on top of the soil once the seeds sprout and show for sets of new leaves will keep the young plants cool and moist. Keep growing, Marianne Binetti