**most of my plant culture information comes from Wikipedia entries, opinions are all my own though.
Lactuca sativa, or lettuce, is a member of the Asteraceae family and actually makes a pretty little white or yellow flower similar to a dandelion if you allow it to bolt and go to seed. When cut its stems ooze a milky white substance, hence the reason for the name Lactuca. Some members of the Lepidoptera butterfly family eat lettuce. In Ancient Egypt lettuce was considered an aphrodisiac.
Lettuce grows best in a humus rich, light soil, with constant moisture. Lettuce prefers temperatures between 75 degrees and 45 degrees F. A hot or dry environment may cause it to turn bitter and bolt, though this is less of a problem with certain bolt-resistant or heat-tolerant varieties. Seeds can be direct sown into the garden or transplanted. With a protective cover to keep lettuce from freezing it can be grown in mild climates nearly year round.
The primary types of lettuce are butterhead, romaine, crisphead or iceberg, and loose leaf. Butterhead leaves have a buttery texture, they are similar to romaine, with less crispness and a shorter growth habit. Romaine, or Cos, grows long leaves with a firm central rib, it is more heat tolerant than other varieties. Crisphead, or iceberg, grows in a tight head similar to cabbage. They have a crunchy texture and are generally the mildest flavored lettuces. Loose leaf lettuce has tender, delicate leaves and doesn't grow a "head" but rather as a bunch of loose leaves. Summer crisp or Batavian lettuce has a mix of traits of iceberg and loose leaf, being crunchy in texture and having only a moderately dense head.
The less bitterness a variety of lettuce has, the higher the water content, and consequently the lower the nutritional value. All lettuce varieties will cross-pollinate easily, so be certain to allow only the cultivars you wish to harvest seed from to go to flower.
Lettuce is a fast grower, taking as little as 3 weeks to reach a harvestable size. Remember to keep your lettuce plants moist, and protected from heat. Slugs are the primary pest to watch for on lettuce, though cutworms can also ruin a planting by cutting the stems when seedlings first sprout. Defeat slugs by baiting, hand picking, or laying down a copper barrier. Protect from cutworms with a paper collar, or start lettuce indoors and move outside once they have a few true leaves on and have grown beyond cutworm edibility. Lettuce can be grown indoors over the winter under a grow light or in a windowsill.
Mix varieties of red, green, and mixed color lettuce in a salad for a more interesting presentation. Since lettuce varieties will cross so easily, try leaving two or three favorite varieties to cross-pollinate and see what exciting new crosses you can come up with. For butterhead, romaine, or loose leaf lettuces harvest only the leaves you need and allow the plant to continue growth; crisphead is best harvested as a whole head.
For planting: try planting lettuces under a fruit tree, in early spring they will receive full sun, and once the tree flowers and begins to put on leaves it will shade the lettuces leaves from the heat of the sun. SFG suggests 4 lettuce plants per square, and they can also be interplanted between taller growing brassicas to protect and shade them. If your tomatoes are ripening and you wish to have lettuces to go with them, try planting lettuce under the shade of the tomato plants, or in a shadier corner of the garden. If all else fails, grow them inside during the hottest part of the year, in the cool of the AC.
You are unlikely to be able to preserve lettuce at all; it manages fine in the fridge for a few days though. Be sure to stagger plantings every few weeks to ensure a crop all year and don't plant too many at once or you'll be swimming in fresh lettuce that HAS to be eaten, and can't be saved by preserving.
Happy lettuce growing!