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Alert: Making Pesticide Applications in School/Community Gardens

Lettuce

Lettuce is a fairly hardy, cool-weather vegetable that thrives when the average daily temperature is between 60 and 70°F. It should be planted in early spring or late summer. At high temperatures, growth is stunted, the leaves may be bitter and the seedstalk forms and elongates rapidly. Some types and varieties of lettuce withstand heat better than others.

There are five distinct types of lettuce: leaf (also called loose-leaf lettuce), Cos or romaine, crisphead, butterhead and stem (also called asparagus lettuce).

Leaf lettuce, the most widely adapted type, produces crisp leaves loosely arranged on the stalk. Nearly every garden has at least a short row of leaf lettuce, making it the most widely planted salad vegetable. Cos or romaine forms an upright, elongated head and is an excellent addition to salads and sandwiches. The butterhead varieties are generally small, loose-heading types that have tender, soft leaves with a delicate sweet flavor. Stem lettuce forms an enlarged seedstalk that is used mainly in stewed, creamed and Chinese dishes.

Crisphead varieties, the iceberg types common at supermarkets all over the country, are adapted to northern conditions and require the most care. In areas without long, cool seasons, they generally are grown from transplants, started early and moved to the garden as soon as the soil can be worked. They are extremely sensitive to heat and must mature before the first hot spell of summer to achieve high-quality heads. If an unseasonably early heat wave hits before they have matured, they almost certainly fail. In many locations, crisphead lettuce plants started in late summer to mature in the cooler weather of fall have a much better chance of success.

Recommended Varieties

Green Leaf

Black-seeded Simpson (earliest to harvest)

Grand Rapids (frilly edges; good for coldframes, greenhouse, garden)

Oak Leaf (resistant to tipburn; good for hot weather)

Red Leaf

Red Fire (ruffles with red edge; slow to bolt)

Red Sails (slowest bolting red leaf lettuce)

Ruby (darkest red of all; resistant to tipburn)

Cos or Romaine

Cimmaron (unique, dark red leaf, Cos type)

Green Towers (early; dark green, large leaves)

Paris Island (long-standing)

Heading or Crisphead

Great Lakes (standard, holds well in warm weather)

Iceburg (medium, size, tender hearts; leaf edges tinged light brown)

Ithaca (tolerates heat; resists bitterness; slow to bolt)

Stem or Asparagus

Celtuce

When to Plant

Leaf, Cos and Butterhead lettuce can be planted anytime in the spring when the soil is dry enough to rake the surface. Two or more successive plantings at 10 to 14 day intervals provide a continuous supply of lettuce. Lettuce does not withstand hot summer days well and spring planting should be completed at least a month before the really hot days of early summer begin. Plantings started in late summer mature during cool fall weather. Watering is essential for seed germination and establishment of seedlings. Some shade may also benefit summer sowings. Heat-tolerant varieties (mainly loose-leaf types) may be grown in the shade of taller crops through most of the summer if extra care is taken about irrigation and soil selection.

Head lettuce must be transplanted in most locations and requires more care than other types of lettuce. Start transplants for a spring crop indoors or in a cold frame and set them in the garden as early in the spring as the weather settles. Harden transplants outdoors so that they become acclimated to the conditions under which they will be grown, but do not allow growth to stop entirely. Cos, butterhead and leaf varieties also can be transplanted for earlier harvest. In the heat of summer, lettuce seedlings started in a protected location in the shade can be transplanted later into moderate sites for some limited success.

Spacing & Depth

Plant seeds 1/4 to 1/2 inch deep (10 seeds per foot) in single, double or triple rows 12 to 18 inches apart. Thin seedlings to 4 inches apart for leaf lettuce and 6 to 8 inches apart for Cos or Butterhead. The seedlings removed may be transplanted or eaten. Transplant Crisphead seedlings 10 to 12 inches apart in the row.

Care

Because lettuce has shallow roots, it should be hoed or cultivated carefully. Frequent light watering causes the leaves to develop rapidly, resulting in high-quality lettuce. Overwatering, especially in heavy soils, can lead to disease, soft growth and scalding or burning of the leaf margins. Organic mulches can help moderate soil temperature and the microenvironment to produce quality lettuce in less than ideal weather conditions.

Harvesting

Leaf lettuce may be cut whenever it is large enough to use. Cutting every other plant at ground level gives the remaining plants more space for growth. Leaf lettuce reaches maximum size (6 to 12 ounces) in 50 to 60 days. Butterhead varieties form small, loose heads that weigh 4 to 8 ounces at harvest (60 to 70 days). The innermost leaves, that tend to blanch themselves, are a delicacy. Cos varieties have an upright growth habit and form a long, medium-dense head.

To store lettuce, wash, drip dry and place in a plastic bag in the refrigerator. Lettuce keeps best at 32°F and high (96%) humidity.

Common Problems

Aphids — Watch for buildup of colonies of aphids on the undersides of the leaves.

For more information on aphids, see our feature in the Bug Review.

Tipburn is a physiological condition that causes lettuce to "die back" at the edges of the leaves. It results from a change in the moisture relationship between the soil and the plant. Clip off any brown leaf tissue and use the remainder of the leaf. Frequent light watering helps to prevent tipburn. Some varieties are resistant to this condition.

Foliage rots can be a problem, especially in hot or wet seasons. Providing good soil and air drainage for the lettuce bed can help to minimize damage in most years.

Questions & Answers

Q. Why didn't my lettuce seeds germinate?

A. Failure of seeds to germinate is caused by insufficient moisture or old seed. Lettuce seed does not keep well and it is advisable to obtain new seed each spring. Store seed for fall gardens in a sealed container in the refrigerator. Some lettuce varieties (especially the white-seeded types) have seed that requires light for germination. These types should not be covered with soil but merely pressed into good contact with finely prepared soil. Care then must be taken to keep the seedbed moist, but not soggy, until the seedlings emerge.

Q. Seedstalks have appeared in the center of my lettuce plants. What should I do?

A. The formation of seedstalks is caused by a combination of long days, warm temperatures and age. When seedstalks begin to form, harvest your lettuce immediately and store it in the refrigerator.

Q. My lettuce tastes bitter. What can I do?

A. Lettuce may become bitter during hot weather and when seedstalks begin to form. Wash and store the leaves in the refrigerator for a day or two. Much of the bitterness will disappear.

Selection & Storage

Iceberg lettuce is the most popular lettuce in the United States. It is a head lettuce that is also low in nutritional value and flavor. Because of its superior shipping qualities, iceberg has been most available which accounts for it popularity. The most abundant nutrient in iceberg lettuce is water. Dark green lettuce leaves always indicate higher fiber, flavor and nutritional value.

Lettuce is a cool weather crop. It can be divided into two categories; head lettuce and leaf lettuce.

Growing lettuce in your garden will give you first hand opportunity to taste fresh flavorful leaves which (unlike iceberg) need little or no dressing. Leaf lettuce and romaine provide flavor and crunch and are excellent salad and sandwich selections.

Lettuce leaves should be free of wilt, rot and rust. Harvest crisp green leaves. Wrap fresh, unwashed leaves in plastic warp and store in the refrigerator for a few days if necessary. Cooler temperature will keep lettuce fresh longer. The coolest part of most refrigerators is usually on the first shelf against the rear wall.

Avoid storing lettuce with apples, pears or bananas. These fruits release ethylene gas, a natural ripening agent, that will cause the lettuce to develop brown spots and decay quickly. Toss lettuce that looks slimy or has black spots. The slime is the residue of bacterial decomposition and the black spots are usually mold.

Nutritional Value & Health Benefits

The nutritional value of lettuce varies with the variety. Lettuce in general provides small amounts of dietary fiber, some carbohydrates, a little protein and a trace of fat. Its most important nutrients are vitamin A and potassium. The vitamin A comes from beta carotene, whose yellow-orange is hidden by green chlorophyll pigments. Beta carotene, of course, is converted to vitamin A in the human body. The darker green, the more beta carotene.

According to the American Cancer Institute and the American Cancer Society, foods rich in vitamin A and C (antioxidants) offer protection against some forms of cancer. Along with other phytochemical, antioxidants reduce the risk of cancer of the respiratory system and intestinal tract.

Lettuce, except iceberg, is also a moderately good source of vitamin C, calcium, iron and copper. The spine and ribs provide dietary fiber, while vitamins and minerals are concentrated in the delicate leaf portion.

Nutrition Facts (One cup raw leaf lettuce, chopped)

Calories 9
Dietary Fiber 1.3
Protein 1 gram
Carbohydrates 1.34 grams
Vitamin A 1456 IU
Vitamin C 13.44
Calcium 20.16
Iron 0.62
Potassium 162.4 mg

Preparation & Serving

Rinse lettuce just before serving in very cold water. Pat dry with a clean towel. Limp leaves can be revived by immersing in ice water for a few minutes. Tear lettuce leaves into pieces. If practical, do not cut or sliced lettuce leaves in advance. Damaged cut lettuce leaves release an ascorbic acid oxidase, which destroys vitamin C. Cut edges also discolor quickly.

Dry leaves before serving. Salad dressing will cling to dry lettuce leaves instead of sinking to the bottom of the salad bowl. Toss with your favorite dressing just before serving (or serve dressing on the side) Lettuce leaves covered with dressing will quickly wilt.

Home Preservation

Due to the extremely high water content, 94.9%, there are no successful method of long-term home preservation for lettuce. Lettuce does not respond well to freezing, canning or drying. For optimal nutritional value, lettuce should be eaten while it is fresh and crisp.

Recipes

The mild flavor of fresh lettuce leaves are well complimented by fresh or dry herbs. The base of most green salads is lettuce. Two or three lettuce varieties are good for both taste and texture. Mix leaf lettuce (Black-seed Simpson or Oak Leaf) with crisp lettuce (romaine or other crisphead) and accent with fresh herb leaves. The simplest way to appreciate a tossed green salad is with a vinaigrette dressing. Keep it simple. When the dressing becomes too complicated, the mild garden greens can be overpowered.

Mixed Green Salad with Red and Yellow Pepper Vinaigrette

  • 4 cups mixed fresh greens (combine a leaf lettuce with crisp varieties) romaine, Boston, with red leaf or Oak Leaf or your favorite lettuce
  • 4 tablespoons Red & Yellow pepper vinaigrette
  • 2 tablespoons crumbled blue cheese or goat cheese (optional)

Wash and dry lettuce leaves. Tear into bite size pieces. Place in an oversized bowl with room for tossing. Place in refrigerator until ready to toss and serve. Can be prepared up to 2 hours in advance. Makes one cup of vinaigrette.

Pour 4 tablespoons of vinaigrette over the greens and toss well with two large forks to coat. Add crumbled cheese, if desired and toss to combine. Serve immediately. Yields 4 one-cup servings.

Red and Yellow Pepper Vinaigrette

  • 1 small yellow bell pepper, finely chopped (about 1/2 cup)
  • 1 small red bell pepper, finely chopped (about 1/2 cup)
  • 4 tablespoons red wine vinegar
  • 2 tablespoons extra-virgin olive oil
  • 2 teaspoons warm water
  • pinch of sugar
  • 1/2 teaspoon salt
  • Freshly ground black pepper to taste

In a medium bowl, whisk together all ingredients until combined well. This vinaigrette will keep, tightly covered, in the refrigerator for 3 days. Recipe may be doubled. Makes one cup.

Try these simple vinaigrette recipes with your favorite salad greens.

Citrus Vinaigrette

  • 1/4 cup fresh orange juice (juice of one small orange)
  • 1/4 cup fresh lemon juice
  • 2 tablespoons olive oil
  • 2 tablespoons canola oil
  • 1/2 teaspoon coarse Kosher salt (1/4 teaspoon table salt)
  • Freshly ground black pepper

Combine the juices and salt and pepper. Slowly whisk in oils until incorporated. A blender or food processor may also be used. Pour into a glass jar and seal. Serve over your favorite salad greens. The vinaigrette will keep, tightly covered, for a week in the refrigerator. To warm cold vinaigrette, place jar in a bowl of hot tap water for a few minutes.

Mustard Chive Vinaigrette

  • 1 tablespoon grainy Dijon-style mustard
  • 1/4 cup finely chopped fresh chives
  • 2 tablespoons white vinegar
  • 1 tablespoon water
  • 2 teaspoons honey
  • 1/4 teaspoon salt
  • 4 tablespoons olive oil

Add freshly ground black pepper to taste.

Using a whisk or fork, in a small bowl combine all ingredients except the oil. Slowly add the oil, whisking vigorously, until the vinaigrette is emulsified. Pour over your favorite salad greens and toss. Store remaining vinaigrette in the refrigerator, in a tightly sealed glass jar, for up to one week. To warm cold vinaigrette, place jar in a small bowl of hot tap water for a few minutes. Makes 1/2 cup.