Soil extremes encourage bolting and bitterness as lettuces begin to mature. These extremes also discourage the rapid growth that is a key to taste and texture in leafy crops. Since harvest takes place when the plants are young, small and tender, you do not have to thin crowded seedlings as you might when growing lettuces and other greens in the usual way. Instead, begin cutting the leaves as soon as the plants are about two inches tall. Harvest Mesclun is at its crispy peak when picked early in the morning before the sun is strong.
Heat causes the leafy plants to wilt.
If you must harvest mesclun during the heat of the day, be sure to allow time to crisp the leaves in cool water before serving. Use scissors to harvest mesclun greens, beginning when they are only a couple of inches high and never let it get more than six inches tall. When you do this, the crop will continue to grow. Mesclun will make an attractive border to a perennial bed and, if you harvest with scissors rather than pulling the plants, they will regrow quickly. Cut leaves just above the growing crowns.