This is a large group of hardy annuals and perennials found wild in various parts of Europe. They are very popular salad plants commonly known as Lettuce. The most commonly grown kinds of Lettuce are derived from Lactuca sativa. These varieties fall into 4 classes, based on their shape and growth. Minor's Lettuce is a different species (see Montia perfoliata), but is also used as a salad green or potherb.
 
Butterhead Lettuce - This is a loose folded, small-headed lettuce surrounded by a rosette of ground hugging leaves. Some kinds are dark green and some are light colored or purple-red. When they are mature, their heads have creamy interiors.
Cos or Romaine Lettuce - This lettuce grows erect and has a cylindrical shaped head that is compact at maturity. It is a medium to light green color with a creamy interior.
 
Crisphead Lettuce - Sometimes mistakenly called "iceburg", which is a named variety within this class, Crisphead Lettuce includes the commercially grown kind familiar in grocery stores and a few dwarf varieties for small gardens.
 
Leaf Lettuce - This is very popular in North American gardens. This plant doesn't produce a head, but plain, rumpled, oaklike or frilly leaves, instead. They range in color from apple green through reddish-bronze.
The next plant described is a variety of Lactuca sativa.
 
Celtuce - Celtuce is also known as Stem Lettuce, Asparagus Lettuce and Chinese Lettuce. Though it has a common name of Celtuce, it is not a cross between Lettuce and Celery. It is just a variety of Lettuce grown for its romaine-like foliage and mainly for its thick, edible stem. The stem grows 6 to 8 inches long and about 1½ inches in diameter. They can be cooked like broccoli and tastes like a cross between a mild summer squash and an artichoke. The leaves can be used for salad.

Lettuce is a cold tolerant, cool weather annual that will bolt to seed in warm weather when the nights grow short. Lettuce isn't suitable for late spring or summer planting because of bolting and farther south the seeds won't germinate in soil warmer than 75 degrees. The soil should be well drained and fertile to force fast growth. The plants should be thinned early and severely to about a foot apart. If they are crowded their development will be checked. Raised beds are beneficial for early spring sowings. Beds of heavy clay should be topped with a ½- to 1-inch deep layer of sand to absorb the sun' s warmth and promote fast growth during cool spring weather.
 
Butterhead Lettuce - Don't grow an excessive amount of this Lettuce because it deteriorates quickly after reaching maturity and can't be frozen or canned. So, plant only a few feet of a row at a time. Begin to harvest lettuce as soon as the thinnings are large enough to eat. Take the whole plant or snap off outer leaves.
 
Cos or Romaine Lettuce - Space these plants 8 to 12 inches apart. Harvest like Butterhead Lettuce.
Crisphead Lettuce - Plants should be set 8 to 12 inches apart. Head lettuce may develop pink or brown interior streaks if the ground isn't kept evenly moist. Start harvesting when the heads are half grown. Cut the entire plant and trim off most of the outer leaves.
 
Leaf Lettuce - Leaf Lettuce is the easiest and most reliable to grow. Combine thinning and harvesting until plants stand far enough apart to reach full size. The whole plant may be pulled or only the outer leaves may be snapped off. Leaf Lettuce, especially the bronze varieties, may turn bitter in hot weather. Refrigerate it 2 to 4 days to reduce bitterness.
 
Celtuce - This grows best in cool seasons. Plant and cultivate like Leaf Lettuce. Space plants 8 to 10 inches apart. Use the young, outer leaves as greens. A few weeks later, the stalks will be ready to harvest. Peeled, they can be eaten raw or cooked.

Butterhead Lettuce - Plant seeds in early spring and again in late summer through fall. The best time is early autumn, when plants have just enough time to mature before the onset of very cold weather. To guarantee heading before hot weather comes, start seedlings inside and transplant them to the garden, but protect from heavy freezes.
 
Cos or Romaine Lettuce - Plant this Lettuce in late summer or fall, so it has plenty of time to form large heads. Romaine takes longer to mature than Leaf and Butterhead. Start and harden off spring plantings indoors; transplant them 2 to 3 weeks before the frost-free date to ensure heading. Set them 8 to 12 inches apart.
 
Crisphead Lettuce - This is the latest to mature so it is impractical as a spring crop where there are less than 60 days after the last hard frost before hot weather arrives. The best thing is to sow seeds in early fall. Thin plants to stand 8 to 12 inches apart. You can start seeds inside 2 to 3 weeks before the last frost free date, protecting them from hard frosts. Seeds will germinate better if they are planted in late summer and shaded to keep the soil cool and thus reduce evaporation.
 
Leaf Lettuce - Sow seeds in early spring and again after the very hot days of summer are over. In cooler climates, you can make 2 to 3 spring plantings, timed 2 weeks apart. Little is gained by starting seeds indoors.
Celtuce - This Lettuce is planted and cultivated like Leaf Lettuce. They should be spaced 8 to 12 inches apart.

Butterhead Lettuce - Cindy, Bibb, Buttercrunch (AAS), Dark Green Boston, Summer Boston, Kagran, Winter Density, Four Seasons (red).
 
Cos or Romaine Lettuce - Parris Island, Valmaine, Ballon.
Crisphead Lettuce - Ithaca, Great Lakes, Premier Great Lakes, Minetto (miniature), Red Grenoble, Valdor (cold-resistant), Tom Thumb (miniature).
 
Leaf Lettuce - Black Seeded Simpson, Grand Rapids, Green Ice, Green Wave, Royal Oak Leaf, Red Sails (AAS), Salad Bowl (AAS), Red Salad Bowl, Slo Bolt, Matchless.
Celtuce -

---

Green Ice Looseleaf Lettuce	Sweet Red Butterhead

---

Little Caesar Cos (Romaine)	Summertime Crisphead Lettuce

---