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Master Gardener Journal  

A   B O U N T I F U L   G A R D E N

Lettuce for the Cool Season

by Laurel Reader, Master Gardener

Lactuca sativa is the botanical name for common garden lettuce. The name is derived from the Latin word "lactis," meaning milk, since a milky white sap is found in the stems and thicker veins of lettuce plants.

Head lettuce (Lactuca sativa capitata), also known as Roundhead or Crisphead, is the most widely sold lettuce. Although many people use the word "Iceberg" to describe head lettuce, Iceberg is but one variety in this category. It's name originated when growers began covering it with piles of crushed ice for shipping in the 1920s. Two other well-known examples of Crisphead lettuce are Imperial and Great Lakes.

Romaine lettuce (Lactuca sativa longifolia) is also referred to as Cos, Roman and Manchester lettuce. The name "Cos" comes from the Greek island where it originated, and the name "Romaine" came into use because it was highly favored in early Rome.

Leaf lettuce (Lactuca sativa crispa) is alternately called Looseleaf lettuce. Simpson lettuce is one of the most popular varieties in the leaf lettuce category.

Butterhead is occasionally referred to as cabbage lettuce. Buttercrunch, Boston and Bibb (also called Limestone) are among the most well known cultivars of the Butterhead family.

Celtuce is also known as Stem Lettuce, Asparagus Lettuce and Chinese Lettuce. It resembles a cross between celery and lettuce, thus the name "cel-tuce."

Of note: Another term you might see is "Mesclun." Mesclun is not a lettuce variety; it is actually mixture of lettuces and/or other leafy vegetables. Other common names for Mesclun are Baby Greens and Salad Mix. A Mesclun mix might include Arugula (Eruca sativa), Cress (Lepidium sativum), Mustard (Brassica spp.), Radicchio (Cichorium intybus), or Endive (Cichorium endivia), to name only a few. The word is derived from the word "mesclumo" (Provençal), meaning mixture.

A favorite of gardeners, lettuce is a basic component in most salads. The word "salad" is said to come from the practice of dipping greens into "sal" or salt.

There are thousands of different lettuce types, all cultivated varieties of the original wild lettuces (Lactuca serriola, Lactuca virosa) of Northern Europe, Asia, North Africa, and parts of North America.

Although lettuce is one of the easiest vegetables to grow, many gardeners-especially desert dwellers-hesitate to try it. Once they learn that the secret lies in choosing the right varieties, however, they often become converts.

Gardeners commonly tuck lettuce into small areas between ornamental flowers and plants. And indeed, there is a lot to be said for the beauty and use of lettuce in an ornamental garden, as a border plant, and as a container companion plant.

Lettuce is a fairly hardy cool-weather vegetable that thrives when average daily temperatures are between 55 and 70 degrees Fahrenheit. Although many forms of this edible perennial (usually grown as an annual) can produce under stressful conditions such as heat, drought and intense sun, it's important to note that high temperatures cause lettuce to bolt, producing seed stalks and bitter tasting leaves before the plants are ready for harvest.

Lettuce is native to Asia and Europe, with some sources reporting that garden lettuce first originated in Turkey or Iran, and others citing a range from Siberia to North Africa.

The Egyptians first cultivated lettuce as early as 4500 BC. Early cultivation was aimed at harvesting the edible oil in the seeds rather than the tasty greens. It may have been considered an aphrodisiac. Egyptian tombs have been found that contain paintings of lettuce with long, pointed leaves resembling Romaine. The Greek physician Hippocrates (born in Cos in 456 BC) believed the milky sap of lettuce would induce sleep. This leafy green vegetable was also popular with the Romans, who believed that Augustus Caesar was cured of a serious illness by eating it. History has it that the emperor actually put up a statue to honor its healing abilities. Early herbalists often used the bitter juice or sap as substitute for opium or laudanum.

The Romans introduced lettuce to Britain. Prior to the 18th century, however, it was mostly eaten cooked. It wasn't until the late 14th century that the English began mixing lettuce with herbs and other greens, and "mingling" it with oil, vinegar and salt-the early salad.

Since those times lettuce and salads have continued to rise in popularity. Modern breeding has concentrated on resistance to disease and bolting, as well as a variety of leaf shapes, flavors and colors. We now consume five times more lettuce per person than we did a century ago, with individual consumption currently exceeding 25 pounds per year.

Lettuce is classified into four major groups based on the plant's growth habits: Looseleaf, Butterhead, Romaine, and Crisphead. A fifth group, somewhat of a novelty, is Celtuce.

Looseleaf varieties form clusters of leaves instead of rounded heads. They mature the earliest, and are best for our short winter/spring conditions since they usually require only 40 to 50 days until maturity. They do not require exacting conditions, tolerating heat, shade and varying soil conditions. These lettuces differ in appearance, with colors ranging from a blonde-green to dark green to red, and leaf texture from smooth to wrinkled to frilly. All are exceptionally tender. They form no heart or head, and the leaves may be picked without cutting the whole plant, allowing for new growth.

Butterhead varieties have small, rounded, loosely folded heads with soft leaves. Leaf color ranges from pale-green to medium-green outer leaves with pale green, cream-colored, or yellowish inner leaves. There are even red varieties such as "Sweet Red Butterhead." Their flavor is sweet, and the leaves are tender and butter-textured. When choosing head lettuce, remember that Butterheads are rarely bitter; they mature quickly (in 50 to 75 days) and are more tolerant of poor soils and weather conditions than Crispheads.

Romaine lettuce produces tall upright plants that are perfect for fitting into tight spots. Their long narrow leaves are fairly stiff and heavy. Although the milky fluid in older leaves can be bitter (yet nutritious), the interior leaves are paler in color and have a sweet, delicate flavor. Regular-sized Romaines mature in 70 to 80 days, but the mini varieties (Little Gem, Little Caesar, etc.) mature as early as 55 to 70 days. Young, tender leaves of all Romaines may be picked as they grow.

Crisphead lettuce produces tight solid heads, usually light green in color due to lower amounts of chlorophyll in the plants. In general, many gardeners find Crisphead lettuce the most difficult to grow, especially in desert gardens. It requires a long season and is intolerant of hot weather, bolting in hot summer conditions. Luckily, "Iceberg" is the most widely available fresh lettuce available in supermarkets.

Although Celtuce is common in Asia, it is less familiar to Westerners. Though the name may imply such (as discussed earlier), it is NOT a cross between lettuce and celery but a variety of lettuce grown for its thick, edible 6-inch stem and Romaine-like foliage. Celtuce stems can be cooked like broccoli and taste somewhat like a mild summer squash or artichoke. The leaves can be used in salads.

Because we have a very short season before the summer heat comes upon us, it is important to choose lettuce varieties that have a short number of days from seeding until harvest. When planting in January, look for maturity within 45 to 60 days. (Harvest numbers are usually found on seed packages and nursery labels). Also, choose heat-tolerant, slow-to-bolt varieties. Good choices are Black Simpson, Slowbolt, Salad Bowl, Little Gem, Tom Thumb, and Red Sails.

Lettuce requires cool conditions, growing best in temperatures between 55 to 70 degrees Fahrenheit. (Seeds fail to germinate, and young plants begin to bolt in temperatures exceeding 85 degrees). Lettuce crops require moist, fertile soil with good texture. Do not plant lettuce in areas with poor drainage. The ideal range of pH for lettuce is 6.0 to 7.0; however, many varieties do well in soils with a higher pH.

Lettuce is happiest in light shade, and actually prefers afternoon shade in our hot climate. Consider interplanting this short-season crop between taller, later-maturing crops. This method exposes tender young plants to the warm sun in the early stage of growth, and allows for increased shade as temperatures begin to rise and surrounding plants gain height.

Lettuce can be planted from September through February, either by direct seeding or by transplanting nursery plants. When starting from seed, sow directly where the plants will grow, and barely cover the seeds (no more than 1/4 inch) with soil. Remember, it is important to keep soil moist for germination to occur. Water lightly to prevent seeds from becoming dislodged, and water often enough to keep the soil from drying out. Thin seedlings as they grow-between 4 to 6 inches apart for leaf lettuce, and 6 to 8 inches apart for Romaine or Butterhead. Use the tender thinnings in salads. When transplanting nursery starts, space plants accordingly.

For the most tender salad greens, grow lettuce quickly by keeping the soil moist and feeding every two weeks with a soluble nitrogen fertilizer.

Never allow your lettuce beds to dry out. Since lettuce is shallow-rooted, keep the soil evenly moist to a depth of about one foot. Mulch the soil around young lettuce plants to maintain even soil moisture, but be careful to keep the mulch away from the plant stems.

Lettuce may need watering up to twice a day in warmer weather. Regular attention to watering will encourage vigorous growth and minimize the development of bitterness in the leaves.

Monitor plants closely and often for pests and disease, making sure to look under the leaves where many pests reside. Aphids, caterpillars, and slugs are common pests of lettuce.

Planting marigolds around lettuce is believed to repel aphids. This method of alternating lettuce with marigolds also increases the beauty of your garden. Insecticidal soap may be used to control aphids as well; just be sure to dilute the spray and test a few leaves first before spraying the entire plant. Be gentle when spraying lettuce; most leaves are quite tender. And don't forget the undersides of leaves where pests might be hiding and doing the most damage.

Bacillus thuringiensis is a safe and effective product for controlling caterpillars.

One way to control slugs is to incorporate a clear dry patch of sharp river sand between their daytime hiding places and their evening meal. Keep the garden clean to eliminate potential hiding places.

Tipburn is a disease condition that causes lettuce to die back around the edges of the leaves. It results from changes in the moisture relationship between the soil and the plant. Frequent light watering helps to prevent this problem, and there are varieties available that are resistant to tipburn.

Foliage rots can be a problem, especially in hot or wet conditions. Providing good drainage and proper air circulation will minimize damage. It is also beneficial to avoid overhead watering; use a soaker hose or drip irrigation covered with mulch to keep the leaves dry and reduce the risk of foliage rot.

Leaf lettuce may be harvested whenever it is large enough to use. Picking just the outer leaves (the "cut-and-come-again" method) is a great way to harvest most types of lettuce, and regular picking will keep plants productive. Remember that lettuce leaves turn bitter as they get older, so frequent picking is important. When plants are mature, cut every other plant to the ground to allow remaining plants more space for growth. If the season is still cool enough, you may want to set out new transplants between the remaining mature plants.

Due to its high water content (nearly 95 percent), there is currently no method of preserving lettuce over the long term. It does not respond well to freezing, canning or drying.

For best flavor and optimal nutrition, eat lettuce just after harvesting while it is fresh and crisp. If it is necessary to store freshly picked lettuce, wrap unwashed leaves in plastic wrap, removing excess air in the wrap, and store in the coolest part of your refrigerator for a few days. Cooler temperature will keep lettuce fresh longer. The ideal temperature should be near 35 degrees Fahrenheit, but do not allow the temperature to go below 32 degrees, as this will damage the leaves.

Avoid storing lettuce with apples, pears or bananas. These fruits release ethylene gas, a natural ripening agent that will cause the lettuce to decay quickly.

Lettuce should be washed in very cold water just before serving. Ice water can revive limp leaves. For salads, pat lettuce dry with a clean towel so that dressings will cling to leaves rather than sinking to the bottom of the bowl. You should tear, not cut, lettuce leaves, since cut edges brown quickly. If possible, wait until just before serving to prepare lettuce. Damaged leaves lose vitamin C rapidly.

The nutritional value of lettuce varies with the variety. The darker the leaves, the higher the content of minerals and carotenoids, including beta-carotene. A green Romaine lettuce leaf can have six times as much beta-carotene as that of a paler Iceberg. All lettuces have high water content and very few calories. Additionally, they provide fiber and folate.

One-quarter pound of Iceberg lettuce provides 14.7 calories, 1.13 g. protein, 2.4 g. carbohydrates, 1.6 g. dietary fiber, 21.5 g. calcium, 374.2 IUs Vitamin A, and 4.4 mg. Vitamin C.

One-quarter pound of Looseleaf lettuce provides 20.4 calories, 1.5 g. protein, 3.9 g. carbohydrates, 2.2 g. dietary fiber, 77.11 mg. calcium, 2154 IUs Vitamin A, and 20.4 mg. Vitamin C.

One-quarter pound of Romaine lettuce provides 18.1 calories, 1.8 g. protein, 2.7 g. carbohydrates, 2.7 g. dietary fiber, 40.8 mg. Calcium, 2948 IUs Vitamin A, and 27.2 mg. Vitamin C.

Brookbank, George. Desert Gardening, Fruits and Vegetables, The Complete Guide. Fisher Books, 1991.

Cromell, Guy & Bradley. Desert Gardening for Beginners. Arizona Master Gardener Press, 1999.

Fish, Kathleen DeVanna. The Gardener's Cookbook. Bon Vivant Press, 1997.

McIntyre, Anne. The Good Health Garden. The Reader's Digest Association, Inc., 1998.

Ogden, Shepherd. The New American Kitchen Garden. National Home Gardening Club, 1997.

Owens, Dave. Extreme Gardening, How to Grow Organic in the Hostile Deserts. Poco Verde Landscape, 2000.

Trout, Darrell. Kitchen Garden Planner. Meredith Books, 1999.

The Organic Gardener's Handbook of Natural Insect and Disease Control. Rodale Press, 1996.

Master Gardener Manual, Chapter 10, pp 100-103.

Maricopa County Master Gardener Volunteer Information
Last Updated December 18, 2003, 2003
Author: Lucy K. Bradley, Extension Agent Urban Horticulture, University of Arizona Cooperative Extension, Maricopa County
© 1997 The University of Arizona, College of Agriculture and Life Sciences, Cooperative Extension in Maricopa County
Comments to 4341 E. Broadway Road, Phoenix, AZ 85040,
Voice: (602) 470-8086 ext. 301, Fax (602) 470-8092