Compositae Genus Lactuca
Place of origin: The Mediterranean region, the interior region of the Middle East
Optimal temperatures for germination 60-70℉ (15-20℃)
Seeds are dormant at 78℉ (25℃) and above.
Optimal temperatures for plant growth 64-75℉ (18~23℃)
Scientific name: Lactuca sativa
Lettuce likes cold weather with little precipitation. When temperatures are below 50OF(10℃), plants grow slowly, and when temperature are above 78OF(25℃), plants tend to bolt. If lettuce plants face a gradual change during their growing period. they can resist temperatures below 27OF(-3℃) and high temperatures above 86OF(30℃) for a short time. Lettuce is drought-resistant but is vulnerable to high humidity. Lettuce is highly adaptable to various soil types and is easily grown.
As the way of growing a head forming lettuce is almost identical as the way for growing a loose leaf lettuce, what follows is the method for growing a head lettuce.
The seeds can be sown in the spring or in the fall from the middle of August to the end of September. When sowing seeds that were saved in the same year, sow seeds that are forced to germinate and sprout at the same time.
Give enough water to seed trays beforehand, and sow each seed around ¾” (2 centimeters) apart. (Lettuce seeds are dormant for 3 months.) Plant seedlings at 3” (6 centimeter) intervals in lines on the ridges with 35-47” (90-120 centimeters) width. As lettuce seeds are heliophious (need light to germinate), cover the seeds with just enough soil so that the seeds can still be glimpsed. If the soil is moist, the seeds do not have to be covered with soil. Instead, press the soil down lightly, and protect the seeds from drying out by placing a cheese-cloth over them. After several days, the seeds will germinate together and the cloth should be removed.
After they germinate, the seedlings need good exposure to sunlight in order to prevent them growing spindly. Water the seedlings moderately, so that the soil doesn’t dry completely out. When growing seeds in the early spring, the seedlings will need to be sheltered from the extreme cold.
When neighboring leaves begin to touch each other, transplant the seedling or plant to is permanent location. The optimal time to transplant is when two leaves emerge after the cotyledon. The width of the ridges is 35-47” (90-120 centimeters), the space between plants is 4” (10 centimeters), and the space between rows is 5” (12 centimeters).
It is important not to plant the seedlings too deeply.
Planting Seedlings in Their Permanent Location
Young seedlings with 3 or 4 leaves after the cotyledon root well, but it is also ok to plant seedlings with 5 or 6 leaves. When growing seedlings in a seedbed, move the seedbed gradually outside for a few days before planting the seedlings.
The width of the ridge and the number of rows change depending on if it is when temperatures are low or if the temperatures are high.
In high-temperatures: plant the seedlings in a line on an 18-24” (45-60 centimeters) wide ridge with 10” (25 centimeters) between seedlings.
In low-temperatures: Planting in seedlings two lines or more lines. When planting in two lines, the ridge should be 36-48” (100-120 centimeters) wide, when planting three lines, the ridge should be 60” (150 centimeters) wide, and when planting in four lines, the ridge should be 70” (180 centimeters) wide. In all cases the space between plants should be about 14” (35 centimeters). It is also possible to zigzag the planting with about 8-10” (20-25 centimeters) between the rows.
If seedlings are planted too deep, their rooting is delayed. It is best to plant the seedling shallowly and not cover the original cotyledon. Good lettuce is produced by giving an ample amount of water, while at the same time by not over watering. Before harvest, don’t water the plants. Excessive watering along with high temperatures causes the lettuce to easily rot.
Seeding in summer and autumn: When temperatures are below 50OF (10℃) and the lettuce plant begins to form a head, cover with a plastic tunnel in order to promote head formation.
Seeding in the spring: As when growing the seedlings, material should be used for moisture retention after planting. If grown in tunnels or greenhouses, manage the temperature by closing or opening the tunnel during the plant’s last half of growth.
To harvest multiple heads of lettuce at one time, work when it is cool outside in order to keep the lettuce fresh. If a leafy ball is formed, the lettuce can be harvested. Don’t harvest lettuce on a rainy day to prevent it from being damaged.
When harvesting is delayed, lettuce begins to have a particular bitter taste, so try to harvest
lettuce in the proper period. Harvest the head along with a few outer leaves. After harvesting, a dry white liquid will emerge from the cut edge. Since the freshness can easily decline, keep the lettuce under 50 OF (10℃) for 3-4 hours after harvesting, as the respiration rate decreases and the shelf life can be improved.