Lettuce

Lettuce (Lactuca sativa) is one of the easiest cool-season vegetables to grow. Although it withstands light frost, sunlight and high summer temperatures usually cause seed stalk formation (bolting) and bitter flavor. Slow-bolting or heat-resistant varieties are available and are recommended for extending the lettuce-growing season.

Most gardeners who grow lettuce raise the loose-leaf type, with either green or reddish leaves. This type is a fast-growing, long-lasting lettuce used for salads and sandwiches. Leaf lettuce basically needs only to be planted and harvested.

Butterhead or Bibb lettuce is a loose-heading type with dark green leaves that are somewhat thicker than those of iceberg lettuce. Butterheads develop a light yellow, buttery appearance and are very attractive in salads. A miniature variety of butterhead, Tom Thumb, is very easy to grow and requires a short growing time. Bibb lettuce will develop bitterness readily if temperatures go above 95 F.

Romaine or cos is less commonly grown by gardeners but is a very nutritious lettuce that deserves attention. It too is relatively easy to grow, forming upright heads with rather wavy, attractive leaves.

Crisphead, also known as iceberg, has a tightly compacted head with crisp, light green leaves. Many South Carolina gardeners find this type difficult to grow due to high temperatures.

Lettuce is a cool-season crop that prefers temperatures of 55 to 65 F for optimum growth. This crop prefers a loamy soil with a high organic matter content. Lettuce seedlings should be protected from the wind because the young plants are rapidly dried out from the wind.

The optimum soil temperature for seed germination is 60 to 80 F. Raw lettuce seed will not germinate at a soil temperature above 95 F. Use primed seed if possible.

Primed seed will ensure optimum seed germination at varying temperatures. Buy only certified fungicide-treated seed from a reputable source.

Plant leaf lettuce in rows 1 to 2 feet apart with seed one-quarter inch deep and 6 to 10 inches apart in the row. It is difficult to space this small seed precisely at the desired spacing; therefore, it will usually be necessary to plant thicker and thin the planting. Leaf lettuce should be thinned when the plants are 1 to 2 inches tall. Leaf lettuce can also be planted in 12-inch-wide beds with the seed broadcast over the bed.

Head lettuce should be planted in rows 3 feet apart with 12 inches between plants in the row. It is best to grow head lettuce from transplants purchased from a reputable garden center.

The soil should be well-prepared to provide good seed-to-soil contact and ensure rapid stand establishment of this small-seeded crop. Soil crusting over the developing seedlings may make it difficult to obtain a good stand, especially on heavy clay soils. Covering the seed with potting soil instead of garden soil will eliminate crusting problems.

A soil test is always the best method for determining the fertilization needs of a crop. Follow the results of a soil test to maintain a soil pH between 5.8 and 6.5 and optimal fertility levels. Information on soil testing is available in HGIC 1652, Soil Testing.

If a soil test has not been taken, apply 5-10-10 at 3 pounds per 100 square feet before planting. Lettuce should be sidedressed once during the growing season. Sidedress with ammonium nitrate (33-0-0) at 1 pound per 100 feet of row or calcium nitrate (15-0-0) at 2 pounds per 100 feet of row. More frequent sidedressing may be required if the garden is sandy or if leaching rains occur. Nitrogen is important for these crops to produce a high-quality, dark green product.

Water the garden frequently to maintain a uniform moisture supply during growth. The garden should be watered in the morning so that the foliage is dry before dark. Water the garden sufficiently to moisten the soil to a depth of 6 inches. Light sprinklings will encourage shallow rooting of the plants. The most critical period for moisture is during stand establishment. It is important to have a constant uniform moisture supply to produce a high-quality crop.

To have a continuous supply of leaf lettuce during the spring and fall, it is best to grow several plantings during each season. Head lettuce is generally more difficult to grow than leaf lettuce. Lettuce does not tolerate hot weather. If this crop is exposed to temperature or moisture stress, the lettuce will usually have a bitter flavor.

Lettuce seedlings are poor competitors with weeds, therefore weed control is very important with this crop. Cultivation for weed control should be shallow to prevent root injury.

Tipburn is a physiological disorder that can occasionally occur on lettuce. It is related to calcium nutrition. Proper soil pH and watering will help avoid this problem.

By using clear or black plastic mulch, wire hoop and clear plastic row covers, excellent lettuce can be grown all winter in South Carolina. On extremely cold nights it may be necessary to cover the clear plastic with a spunbond-type row cover material.

Leaf lettuce should be ready to harvest about 75 days after planting. It can be used as soon as plants are 5 to 6 inches tall. Bibb lettuce is mature when leaves begin to cup inward to form a loose head. Cos or Romaine is ready to use when the leaves have elongated and overlap to form a fairly tight head about 6 to 8 inches tall.

Head lettuce can be harvested as early as 55 days, depending on the variety. It is mature when leaves overlap to form a head similar to those available in the stores.

Store in the refrigerator in the coolest area. Crisphead lettuce can be stored for two weeks under optimal conditions. Leaf and Bibb will store as long as four weeks if the leaves are dry when bagged.

Insect problems that may be encountered with this crop include aphids, cabbage looper, corn earworm and leafhoppers. Diseases include gray mold, Rhizoctonia bottom rot and Sclerotinia drop.