I typically sow several seeds in a small pot. Do I have to wait for the first set of true leaves before I transplant seedlings? What happens if I don't.
Seedlings are very delicate. The initial seed leaves or cotyledons are actually a part of the embryo. They provide food reserves to enable the plant to begin growth. Some die off quickly while others persist. In any case, they are essential to the health of the plants, and should not be handled.
The first "true" leaves are structural different than cotyledons. Once the true leaves are big enough to handle by the leaf, you can try replanting them. Never handle the seedling by the stem since damage in this part of the plant will likely result in death.