Most vegetable seedlings are long-day plants that thrive with 16 hours of light (and 8 hours of dark). An artificial light is the easiest way to achieve this, especially for northern gardeners with short growing seasons.
While warmer temperatures between 75°F and 80°F are ideal for germination, most seedlings grow best at a high of 65°F to 70°F during the day and a low of 55°F to 60°F at night.
Bottom watering ensures the entire seed starting medium is moist and encourages roots to spread downward.
To promote good plant health and keep seedlings from stretching for light, space them no less than an inch or two apart once they develop the first true leaves.
This simple motion simulates an outdoor breeze and tricks the seedlings into thinking they need to grow thicker stems to hold up against windy conditions.