Slice the top off the empty egg carton carefully, using a sharp utility knife. Set the top aside for later use.
Use the nail to poke a small hole in the center of the bottom of each egg cup. Proper drainage is crucial for basil to thrive.
Fill the egg cups to the top with the potting soil. Add a few drops of water to each section to moisten the soil. Avoid overwatering -- the soil should be slightly damp, not soggy. Keep the soil damp by checking daily and watering if the soil appears dry.
Put three to four seeds in each cup. Gently press them into the soil about 1/4 inch. Slip the top of the carton beneath the container for a handy tray.
Place the seed tray in a sunny window, preferably on the south side of your house. If there is less than full sun for six hours a day you may need to place the seeds under a fluorescent light for up to 10 hours a day.
Remove the seedlings from the egg carton after germination by gently squeezing the bottom of each section in turn to loosen the soil so you can gently hold onto the seedling and its dirt. Germination takes about one week. Transplant the 1-inch seedlings into a bigger pot or outdoors.