Seedlings of different species require different conditions for best growth. In some species, the seedling prefers a temperature different from the germination temperature. Read your seed packet, and pick out ahead of time favorable places to move your seedling flat after emergence.
After emerging, your seedlings should be moved into a desirable location; your seed packet will indicate desired light and temperature. All seedlings need light to develop into strong, healthy plants. In dim light they will grow too tall, with weak, spindly stems. Fluorescent grow-lamps, greenhouses, or cold frames are a big help, but protected beds or sunny windowsills work well also. Avoid cold drafts for warmth-loving kinds.
Seedlings also need air circulation for good health, so avoid locations that are too closed-in. Remove the clear plastic cover from the flat as soon as emergence occurs.
Check the moisture of your growing medium in the flat. Air movement, bright light and warmth, while needed, also cause fast drying. Keep the medium less moist than while seeds were actually germinating, but still don't let its surface dry completely, until your seedlings grow a little bigger. You may need to cut watering back to every second or third day, rather than daily.
Watch seedling stems carefully. If some of them fall down, the base turning brown and collapsing though the leaves still look good, this may indicate "damping-off". This is a disease that is encouraged by too-wet soil and poor ventilation. Reduce watering and increase ventilation. A fungicidal drench may also help.
Seedlings whose leaves droop or shrivel, or whose stems, though not discolored, bend over along their entire length, are probably too dry, so soak the flat thoroughly.
You can begin feeding your seedlings even before they emerge! When you water your seedling flats, simply use a weak fertilizer solution instead of plain water. We recommend 1/4 teaspoon of Park-Start
Transplanting Seedlings from a Seedling Flat or Seedbed
When seeds have been sown close together in a flat, the seedlings grow together rather quickly. They soon become overcrowded, tall and spindly (this is why seeds should be sown thinly to begin with) from stretching in competition for light. After 4 true leaves have developed, and as soon as they begin to touch one another, it's time to transplant seedlings into pots or into a Bedding Plant Kit, where they will have more space.
Follow these steps in transplanting:
Transplanting from Park's Bio-Domes, Park-Starts
If you have sown seed into one of these kits, you can skip most of the steps for transplanting. As the seedlings grow larger and begin to touch, either space them further apart, if possible, or plant them into appropiate sized pots to avoid transplant shock. Or you may set them directly in the garden if the weather is right.