Salad greens will grow well in almost any container as long as it has adequate drainage holes. Fill the container with bagged potting soil to which 1 tablespoon of slow-release organic fertilizer has been added.
Mesclun is the French term for a mix of salad greens. The traditional mesclun mix contains various tender lettuces such as chicory, arugula and endive. Sprinkle the seeds over the top of the soil, aiming to get them about 1" apart. Cover the seeds with 1/4" of potting soil. Water well.
Keep the soil moist until the seeds sprout. There is no need to thin the seedlings as crowding maintains moisture and prevents weeds.
In a matter of weeks, the container should be covered with tender green plants. To harvest, snip heads of lettuces at soil level to create more room for nearby heads. Lettuce heads will continue to grow new leaves, so harvest just the outer leaves of the heads that remain after thinning.