Egg cartons are a great biodegradable way to do seed-start gardening. Simply cut off the sides and lid from your carton.
Place the cut lid under the carton base to catch leaking water.
Fill the holes three-quarters full with potting soil. Place your seeds in the soil then cover them with a thin layer of the potting soil. Mist as needed to germinate. If you're using a different type of egg container, such as plastic, which doesn't drain, just punch a tiny hole in the bottom of each egg bed.
Paper egg crates can be transformed into these cute mini egg carton planters. Use them for starts or tiny plantings. This page contains a step up step project for making these outdoor planters.