Planting strawberry seeds in cardboard egg cartons is a great way to recycle something that would otherwise go into a landfill and a fun way to grow strawberries, especially for kids. When you're ready to plant the seedlings outdoors, cut apart the egg carton and plant the seedling, cardboard and all. Start strawberry seeds indoors about a month before the last freeze of the season.
Fill the cells of a cardboard egg carton about two-thirds full with commercial potting soil. Sprinkle a few strawberry seeds on top, and cover with a thin layer of potting soil.
Mist the soil with a spray bottle and cover the egg carton with plastic wrap. Put the egg carton in a warm place where it will get light, but don't put it on a windowsill. It will get too hot there and the seeds won't germinate.
Remove the plastic and mist the soil if it appears dry. It won't require much water, because the plastic will keep the environment humid.
Watch for the strawberry seedlings to emerge in a few days, and then remove the plastic. Put the egg carton where it will continue to receive indirect sunlight, and keep the soil moist until you're ready to plant the strawberry seedlings outdoors.
Plant the seedlings in well-worked soil when the weather warms in spring, and there's no danger of frost. Cut the carton apart in sections and plant each seedling in its cardboard "pot," which is biodegradable.