Lettuce: A Garden Essential
by Steve Peters

Of all the plants that we grow in our gardens, the most popular, except for perhaps the tomato, is lettuce. It is easy to grow but must be eaten fresh to enjoy its full benefits as a refreshing, delicately sweet food. Most lettuce leaves, when broken, exude a small amount of white, milky liquid, which can also give lettuce a slightly bitter, more complex flavor that is often underappreciated. The presence of this "milk" is the reason why lettuce's scientific name is Lactuca sativa, since Lactuca is derived from the Latin word for milk. Although lettuce is often not highly regarded for its nutritional benefits, other than maybe dietary fiber, it is actually a very nutritious food. In particular, it is an excellent source of beta-carotene (a precursor of vitamin A), vitamin C, folic acid, manganese, and chromium.

Lettuce is native to the eastern Mediterranean region and western Asia. It has been in cultivation for several thousand years and was held in high regard for its therapeutic properties by the Egyptians, Greeks, and Romans. Lactuca sativa, cultivated lettuce, is closely related to wild lettuce, Lactuca scariola, which is a common weed throughout the United States. Lettuce is an annual crop belonging to the Asteraceae (Composite) family, the largest family of dicotyledonous plants, which includes sunflowers, zinnias, chicory, thistle, and many other lesser-known tribes.

Varieties
Lettuce is often categorized into four main types, which are recognized as subspecies or botanical varieties. These are 1) head (var. capitata) which includes iceberg, crisphead, and butterhead; 2) romaine or cos (var. longifolia); 3) looseleaf (var. crispa); and 4) asparagus or stem (var. asparagina).

The most widely grown commercial varieties are iceberg and crisphead types. These lettuces, however, tend to require a long season of moderate temperatures, such as that found in the famous coastal area in California, the Salinas Valley. Many home gardeners live in less than ideal environments for these types to thrive. Therefore, when most of us choose an iceberg or crisphead lettuce for the home garden, it is best to identify varieties that are more heat tolerant and are slow to bolt (i.e., go to seed). The beauty of these lettuces is that they provide a distinctive, mouth-watering crunch to a garden salad. While perhaps the least nutritious lettuce type, icebergs and crispheads still contain substantial quantities of folic acid and dietary fiber. A great example is Reine Des Glaces, which is somewhat heat tolerant and has a juicy crunch and distinctive frilly outer wrapper leaves that are attractive in a salad.

Butterhead lettuce, like iceberg, forms a compact head but is often considered a separate type. It has a soft, buttery texture and a delicately sweet flavor. The heads tend to be looser than an iceberg and the leaves are thicker. The outer leaves, in varying shades of green and red, are large and ruffled, while the inner, blanched leaves are extremely tender and cream colored. While they may not hold in the field as long as an iceberg—becoming bitter if not harvested fairly young—butterheads are more tolerant of a wide range of soil and weather conditions. Pirat is a gorgeous, light-red butterhead with a tender, compact heart. Sucrine is really a butter/romaine cross, yet it has that distinctively buttery texture and tight, savoyed leaves that hold up well in a salad.

Looseleaf lettuces are the easiest to grow since they don't form a head and can be harvested as individual leaves for several weeks (cut and come again). They come in a wide array of thick, thin, savoyed, flat, frilly, red, green, or speckled leaves. As they often are the quickest lettuces to bolt during the summer heat, they are typically grown during spring or late summer into fall. Some excellent varieties include Oscarde, a compact plant with deep-red, oak-shaped leaves; Thai Green, a light-green leafed and extremely heat-tolerant variety; and Green Deer Tongue, a distinctly pointed leaf shape with a slightly crispy yet buttery texture.

Romaine or cos lettuce has a columnar, upright form, and is best known for its crunchy texture, sweet, crispy heart, and sturdy outer leaves. It is also the most nutritionally rich type of lettuce. Like looseleafs, these tend to bolt and turn bitter in the summer heat, but they are exceptional under slightly cooler conditions and store better after harvesting than the other types. Superb varieties of this type include Jericho, a light-green plant with a large, dense head that is bolt resistant and stays sweet in hot weather; Forrellenschluss (German for "speckled like a trout's back"), a looser-leafed romaine with distinctive bronze speckles; and Cosmo-Savoy, a large, fast-growing, deeply savoyed variety that grows best in the fall.

Culture
Lettuce is best adapted to growing in relatively cool conditions, with an optimum temperature from 60 to 70°F. Some varieties will tolerate daytime temperatures up to 85°F providing that the nighttime temperatures are cool (below 60°F). Modification of the environment, however, is always an option. For example, in hot climates, shade cloth can be used to reduce intense sunlight, and misting plants throughout the day can cool leaf surfaces. Also, lettuce can thrive during the colder winter months when grown under cloches or cold frames.

Lettuce tolerates a wide range of soil types from clay loam to sandy loam and even muck (organic) soils, providing they are well drained. It is best grown on slightly acidic soils (6.0 to 6.7 pH) with high fertility and reasonably high levels of organic matter and water-holding capacity. Spreading a layer of high-quality, mature compost and lightly mixing it in the upper 2–3 inches of soil ensures that the shallow-rooted lettuce plants will receive the nutrients they need.

Direct seeding and transplanting are both good planting methods depending on the situation. If you have a smooth, clean seedbed that is easy to plant into, and it is likely that the next 60 or 70 days will have relatively moderate temperatures, then direct seeding usually works great. In coastal areas, this condition could exist for several months, while in interior, continental climates the best opportunity is in late summer with a midfall harvest. Direct seeding, however, almost always requires thinning, which can be tedious. Starting your plants indoors and then transplanting them in the field 4–6 weeks later is advantageous when you want to get an early jump on the season, and when your ideal window for growing lettuce is limited. This most often occurs in the spring when there are a few weeks of 65–70°F weather, and then it suddenly is summer and 90°F. Transplanting requires more initial labor, but is timesaving later, since thinning is unnecessary; in addition, transplanting may allow another crop to be grown before the lettuce is transplanted.

Because of the huge diversity of lettuce types with varying textures, shapes, colors, and growth habits, it is not necessary or even appropriate to always grow it to the full, mature head stage. Many lettuces can be harvested at the baby-leaf stage, which is as early as 15 to 25 days after planting. These varieties tend to be highly textured or savoyed and keep their "loft" in a mixed salad. Teenage or adolescent lettuce is harvested 25 to 40 days after planting, is great in mixed salads, and is more nutritious than the baby leaf. Finally, there is the mature stage, 40 to 65 days after planting. These full heads are the most nutritious and keep longest in storage. Crisphead lettuces can store for up to 2 weeks, romaines for about 10 days, and looseleaf types for about 4 days before they lose their freshness.

Several diseases can affect lettuce, although they rarely cause serious damage and can usually be minimized with cultural methods or choosing the appropriate varieties. Bottom rot (Rhizoctonia solani) is a fungal disease that causes damping-off of seedlings, and in more mature plants, a slimy, brown rot on the underside of leaves. It occurs during wet weather and is alleviated by growing plants on ridges, removing infected leaves and debris that accumulate underneath the plants, and avoiding additional watering. Romaine varieties, with their upright stature, are less susceptible to this disease. Downy mildew (Bremia lactucae) is a fungal pathogen present in cool, coastal areas. As in controlling bottom rot, avoid over watering, practice clean cultivation, and also eliminate nearby wild lettuce, which is a host for the disease organism. Regular crop rotation helps alleviates these and many other diseases. Another common malady is tipburn, which is not actually a disease but an abiotic physiological disorder. It produces brown spots along leaf margins, which can ultimately affect the inner leaves. It generally occurs during hot weather when the plants are growing rapidly. Foliar spraying with liquid calcium can mitigate its effects, and crisphead varieties generally exhibit more tolerance than other lettuce types.

Storage and Preparation
Lettuce is meant to be eaten as fresh as possible. Wilted leaves should be avoided, and any leaves with slimy, brown or yellow spots should be discarded. Romaine and leaf lettuces in particular should be washed and dried before they are stored in a refrigerator. A salad spinner is great for removing excess moisture. Wrapping the leaves in a clean, damp cloth and then placing them in a plastic bag before refrigerating will ensure the longest lasting, crispiest lettuce. Romaines can store for up to a week this way, while leaf lettuces last 2 to 3 days at maximum freshness. With butterhead and crisphead types, remove the outer leaves if they are discolored, and then refrigerate the whole head without washing. Butterheads will still only retain their freshness for 2 to 3 days, but crispheads can last for up to 10 days.

Just before eating, remove any remaining discolored leaves and chop off the bottom root portion. Leaves can be broken up by hand into mouth-sized pieces or cut into bits with a sharp kitchen knife. Include other dark green and colorful greens such as arugula, endive, radicchio, cress, and mustard to add zest, nutrition, and excitement. Place all of these leafy plants into a bowl of water and swish them around with your hands to allow sand and dirt to sink to the bottom. Repeat this rinsing and then dry in a salad spinner. Carrots, beets, cucumbers, celery, tomatoes, peppers, toasted nuts and seeds, croutons, fruits, and many other foods can also be added to create your one-of-a-kind gourmet salad that may not be found in even the finest five-star restaurants.

Dan's Dressing
Try this homemade dressing from Dan, our guy in marketing. It always gets rave reviews. You'll need:

• 1 cup oil, preferably organic olive or canola
• ¼ cup vinegar, preferably red wine
• 2 tsp brown or Dijon-type mustard
• 2 minced/crushed organic garlic cloves
• 1 tsp sugar