Starting seedlings indoors in winter, when the light levels are still low from outside, calls for supplemental lighting. The top leaves of each seedling needs to be kept only a few inches from the light source. This will keep seedlings compact and strong, and prevent them from getting tall and leggy. Their energy will go into leaf production rather than growing tall and spindly. With the right lighting, you can grow all plants, including many food crops, indoors year round.