Lettuce will germinate between 2 days and 2 weeks, depending on the temperature. 60 degrees is ideal. Lettuce that is direct seeded in the garden can take temperatures as low as 20 degrees once it is growing. When your plants are about 4″ high, they should be thinned to about 4 plants per square foot. You can easily transplant the thinnings as lettuce does not mind root disturbance. This transplanting will slow them down a bit, but that is advantageous. It will help extend the harvest and something that I always practice. Lettuce should grow quickly to get the best quality. This means do not let them get crowded, do not let them get overrun by competing weeds, and keep them well watered, especially in warm weather. I strongly promote the use of mulch. It will keep the soil cooler and hold moisture. It also keeps the lettuce cleaner. When rain hits a leaf mulch, it doesn’t splatter dirt onto the lettuce leaves.
Do not water very tender plants in the hot sun. It will tend to cook them. Rather, water them in the early morning or late afternoon/evening. You can feed the plants liquid kelp or a compost tea about a month before harvest to improve their size. Harvest plants 50 – 100 days after planting. We usually harvest by taking off the larger leaves on the bottom of the plant. Leave the smaller top leaves and allow the plant to continue to produce. The other option is to allow the plant to grow to maturity, which would be 12-18″ across and cut the whole plant off at the base. It is best harvested on the day you plan to eat it. If you must store it for a few days in the refrigerator, do NOT wash it until you are ready to use it. It will store better unwashed.
Fresh heirloom lettuce from the garden is wonderful! There is absolutely nothing in a grocery store to compare with it.
Saving heirloom lettuce seed is easy. Let the plant continue to grow and it will eventually shoot up a flower stalk around 2ft. tall. This will flower and then go to seed. I suggest you let some of your spring lettuce go to seed. In the fall, you may get frost before the seed develops and in the rains, it will not dry as well. When the seed is mostly dry, I cut the seed heads into a paper bag. Store the bag in a warm dry place for a few weeks. Then sift out most of the chaff. It is not a problem if there is fine chaff still with the seed. Store the seed in a cool dry place, the refirgerator in a glass jar with a tight lid is ideal.
Heirloom lettuce is very easy to grow. You can even grow it in a flower bed on in a large pot. Delicious!!