Adding leafy vegetables to your garden allows you to begin harvesting in early spring, often before warm-weather vegetables are even in the ground. Leaf lettuce, spinach and head lettuce are the most commonly grown leafy vegetables in home gardens. Most are ready for first harvest within two months, and they then continue to produce until the summer heat causes them to go to seed. It is best to start leafy vegetable seeds indoors for later transplanting, according to the Penn State College of Agricultural Research.
Fill a seed-starting flat with a well-draining potting mix. Sow the seeds at the spacing recommended on the seed packet, generally providing 2 inches of space between seeds in all directions. Sow seeds on the soil surface if the seed packet indicates light is necessary for germination; otherwise sow seeds approximately 1/4 inch deep.
Set the flat into a tray of water. Leave the flat in place until the soil surface becomes moist from absorbing the moisture. Drain the excess water from the tray, then set the flat back in the tray.
Cover the flat with a layer of plastic wrap. Place the flats in a 65- to 70-degree F room to germinate. Place flats in an area that receives indirect light if seeds require light for germination. Most leafy greens germinate within seven to 10 days of sowing.
Remove the plastic wrap once seedlings appear. Place the flat in a sunny window sill and water the soil from the bottom as before when the top of the soil begins to feel dry to the touch.
Harden off greens for transplanting when they are four to five weeks old. Set the flats outdoors in a protected area during the daytime for three to seven days before transplanting. Move the flats gradually into direct light over the course of the week to accustom them to outdoor conditions and temperatures.
Plant the greens into a full-sun, well-drained garden bed at the same depth they were at in the seedling flat. Space plants based on the recommendation on the seed packet. In general, space leaf lettuce 6 inches apart, head lettuce 12 inches apart and spinach 4 inches apart.
Water the greens when the top 1 inch of soil begins to feel dry, usually once a week. Irrigate in the morning until the top 6 inches of soil feels moist. Morning watering ensures the leaves on the plants dry before temperatures cool down at night.
Harvest the outer leaves of leaf lettuce and spinach when they reach the desired length, usually about 6 inches. Leave the inner leaves in place to continue production. Harvest head lettuce when the heads are firm but not hard by cutting them off the plant at the base.