Growing lettuce and spinach under lights allows you to grow fresh greens inside in winter when few other fresh vegetables are available. These plants are suitable for fresh salads, or the spinach can be cooked in a variety of recipes. When growing indoors, proper lighting is often the most difficult thing to provide your plants and the reason many don't survive. Using grow lights, available at most stores that sell light bulbs, allows you to provide the proper spectrum of lights for your spinach and lettuce to thrive.
Fill seedling pots with a soilless potting mix. Soilless mixes drain well, providing an optimum medium for indoor growing.
Sow one to two seeds per pot. For lettuce and spinach, place seeds directly on the soil surface and cover with a 1/4-inch layer of soil. Mist the soil with water until it is moist, then cover the pot with a layer of plastic wrap.
Set the seed pots in a warm room, 70 to 75 degrees Fahrenheit, to germinate. Lettuce and spinach usually germinate within seven days.
Remove the plastic when seedlings emerge. Place the pots under grow lights so the lights are positioned 6 inches above the top of the seedlings. Leave the lights on for 16 hours a day.
Water the seedlings when the soil surface begins to dry, keeping them evenly moist at all times. Water once a week with a soluble fertilizer, following the application rates detailed on the fertilizer package.
Transplant the lettuce and spinach plants into individual 9- to 12-inch pots once the plants are 3 inches tall. Fill the new pots with potting mix and plant one plant per pot to the same depth as in its nursery pot.
Adjust the height of the grow lights as the plants grow, maintaining the 6-inch distance between the plants and the light. Keep the soil moist but not soggy.
Harvest the outer leaves from the lettuce and spinach as needed. Cut them off at the base of the plant and use within one to three days.