Getting seeds started indoors can be as simple as re-purposing pressed-paper egg cartons. Egg carton cups are just the right size for starting seeds and growing seedlings on to size. Half egg shells and newspaper cones set in egg carton compartments will work just as well.
Poke a hole in the bottom of each egg compartment (or egg shell or newspaper cone) and fill with moistened sterile seed starting mix. Use the egg carton lid as a tray beneath the compartments.
Sow two or three seeds in each compartment and just cover them with seed starting mix; the rule of thumb is to cover seeds to a depth of three times their diameter.
Use a clear plastic bag as your seed-starting greenhouse. Place the egg carton in the plastic bag (don’t tie the bag–germinating seeds need fresh air) and set it in a warm, light place–on a kitchen countertop or under fluorescent lights. A consistent temperature of about 70 to 75°F is best to ensure quick sprouting. Keep the starting mix just moist until seeds germinate; remove the plastic bag if mold should start to grow.
When the seeds germinate (you’ll see green shoots), take the carton from the plastic bag and set it in a light but not too bright windowsill. (Direct sunlight through window glass may burn young seedlings.)
Let the seedlings grow two weeks–enough time to form true leaves–then use a small scissors to snip away the smaller and weakest of the seedlings at soil level. Leave the strongest seedling to thrive. (Avoid pulling seedlings from their starting compartments so as not to disturb young roots.)
Grow seedlings on for another two weeks being sure to keep the soil just moist–do not let seed-starting mix dry out. Use a liquid organic fertilizer at quarter strength when you water new seedlings. When more than two sets of leaves have emerged, give the seedlings up to one-third strength liquid fertilizer.
Four to six weeks after germination, indoor started seedlings will be ready for potting up or transplanting out in the garden. Before seedlings go into the garden they should be hardened off–placed in a sheltered outdoor place for a few hours each day and allowed to acclimatize to outdoor conditions, a process that can take up to two weeks depending upon the weather.
Once seedlings are hardened off, the seed-starting egg cartons, egg shells, or paper cones can be gently crushed or cut apart and then transplanted whole into the garden without disturbing the seedlings’ roots. Egg cartons, egg shells, and newspaper cones will decompose quickly once set in the ground. Most seedlings should be planted no deeper than they were in the seed-starting container.
Starting seeds indoors can give you a four to six-weed week head start over seeds sown directly in the garden.