According to the U.S. Department of Agriculture, zone 5 is most of the midwestern United States and parts of the Pacific Northwest and New England. Winters are long in zone 5, and springs can be unpredictable, with the occasional scorching heat wave or late, killing frost. If you want an early harvest in your vegetable garden, it's a good strategy to start seedlings indoors under grow lights in early April if you want healthy seedlings to plant by Memorial Day.
Buy fluorescent tube lights and fixtures. Whether you grow seedlings with these fixtures as a supplement to natural light or by themselves doesn't matter. The goal is to give growing seedlings at least 14 hours of strong light per day.
Fill flats with soilless potting medium. Plant or sow seeds according to the instructions on the packet. Moisten the medium, and cover the flats with plastic wrap to keep them from drying out while you wait for germination. Keep out of direct sunlight during this period.
When seeds germinate, remove the plastic and place flats on large tables beneath the fluorescent tubes. Position the lamps about 4 inches above the seedlings.
Expose the seedlings to 14 to 16 hours of this type of light per day to grow healthy seedlings with strong stems. After they get their third set of true leaves, seedlings can be moved to individual pots, and within a week or two, planted outdoors.