(in zone 5a)
My system uses three types of lettuce. Crisp heading types such as Gemini , Ithaca, or Summertime are sown in the spring for harvest during each week in June. These are "cut and come again" types, however the hot weather usually causes them to bolt after the second cutting. A loose heading Batavia lettuce such as Sierra or Nevada is sown in May, for harvest each day during the summer. Batavia lettuce can be cut again and again without bolting.
The supreme of all lettuce, Jade Pagoda - Michihili, a Chinese cabbage, is sown on July 1st for table use during October. A second sowing is made before the end of July for final harvest in November, but actually the exact day on which a killing frost (26º or less) is forecast for that night. Fourteen to eighteen heads of michihili are placed in a large refrigerator in the freeze-protected (36º) garage. This lettuce lasts in perfect condition through the end of May. Each head weighs from four to ten pounds, and there is little resemblance to those skinny heads of Chinese cabbage seen in the supermarkets. Here are the growing details:
Crisp head lettuce is a cool weather crop which requires well drained soils, but constant moisture. These lettuces often require shading from overhead and afternoon sun. The Batavia and Michihili lettuces love the sun. Lettuce requires neutral soils high in nitrogen. No controls for insects are required with the proper soils.
The Michihili, crisp head, and Batavia style lettuce are sown in ordinary garden soils which carried onions during the previous season. Since I use a little calcium nitrate and garden compost for fertilizing onion rows, these are ideal the following season for lettuce, with no further amendment. All of the looseleaf varieties are sown in soils manufactured from ground up Christmas trees. This soil has a very high moisture retention in the hottest temperatures without becoming wet because they drain rapidly. This type of soil is so friable and loose that root growth and travel are not impeded. The pH is constant at 6.5 and requires no liming. Slugs hate this type of soil.
Seeds for the Crisphead lettuces are sown indoors on March 12th, and transplanted to their permanent site in April. All other seeds are sown directly. Lettuce seed must have light to germinate. I like to make a shallow furrow in the soil, sow the seeds, then cover the furrows with a dusting of peat based germination mix to retain moisture.
I use a 60% shadecloth stapled to 2ft x 8ft and 4ft x 8ft lattice panels. These are light in weight and easy to move from one patch of lettuce to another. They are placed on supports like pepper cages, and have proved wind resistant. Another panel leans against the West side of the patch to protect from late afternoon sun. A lath house would be nice.
All plots use drip hose manufactured from recycled auto tires. The longevity of this type of hose is preserved by careful control of water pressure. Since each plot has its own water tap, I simply control the pressure by opening the tap only the amount necessary to get the hose to start to drip. If the hose is emitting fine sprays of water into the air, the lettuce will get wet, and the life of the hose will be diminished over time. Without a constant supply of moisture, every variety of lettuce will bolt sooner, and will develop a sharp taste. Like tomatoes, lettuce does best if soil moisture does not change from one day to the next. I apply only enough water to keep the roots in moisture, but not enough to moisten the soil at the surface. It is important to check the moisture levels daily if the surface of the soil is dry.
I prefer the Michihili lettuce above all others because of its sweet flavor and its variable crunchy textures. It does not have the rubbery texture or the cabbage flavor of other Chinese cabbages, all of which require cooking. I especially like it and the crisp heading Gemini or Ithaca because no water washing of the lettuce is required. Once the outer wrappers have been peeled off, even a lazy man can put his own salad together.
Starting from the base, I cut the Michihili heads into 3/8" thick slices as you would cut a loaf of bread. As you place the slices into a lettuce crisper or into vegetable storage bags (with holes), they break up into individual strips ranging from 2 to 6 inches long. Each strip is thick and crunchy in the center tapering off to leaf at each end. The strips are pleasant to eat as is, and when in salad, respond well to every type of dressing.
While in storage in the garage refrigerator, it is best to stack the heads vertically. When that is not possible, they should not be stacked more than two high, as they do best when there is plenty of air circulation. By March, the heads are attempting to search for water with fine white root hairs at the crown. Do not mistake the root hairs for mold. If your lettuce is going to rot, it will do so from the inside out, and you should not notice any softening of the centers until near the end of May depending upon refrigerator temperature which should average about 35ºF.
I should repeat the importance of allowing the Michihili to suffer several light frosts before harvest, as this is the source of the sweet flavor. Once frozen, however, the lettuce has no further value as a raw vegetable, so it is important to make your harvest on the day on which you have received your first weather report of an expected killing frost (26º or less).
While I am fond of all the lettuce I grow, I would not grow any of the other lettuces if I could have Michihili all year long. The method described is a lot of work, but if you really love your salads, you will grow as many varieties of lettuce as you have room for.