Many species germinate within a few weeks. When the seedlings first appear, they look like tiny green spheres. After they have sprouted, replace the Tupperware lid with a piece of stretched muslin secured with string or a rubber band. This will allow air circulation, which can be increased by placing a fan above the container. Adequate air circulation is essential as all green plants require plenty of CO2 to grow.
Seedlings are more sensitive to light than mature plants.
They should be dark green. If they are a reddish or brown color, they are receiving too much light, and additional pieces of muslin must be placed over the top of the container to shade them. If they are yellowish then they are not getting enough light. When the seedlings have germinated, place a thin layer of very fine aquarium gravel on the surface of the soil. This gravel will help to support the new seedlings and protect the surface from drying out too quickly.