University of Maryland Extension

Lettuce

lettuce

  • Hardiness: Hardy annual (can withstand light frosts but needs protection against heavy frosts or freezing).
  • Planting: Sow leaf or butterhead types as soon as soil can be worked in the spring, or in late summer. Crisphead and cos (Romain) types may be transplanted in early spring and fall. Tolerates partial shade (4-6 hours of direct light/day) but grows well with full sun in spring and fall. Baby leaf lettuce can be grown entirely in indirect light in summer.
  • Days to maturity: 40 - 80, depending on type.
  • Spacing: Leaf, cos, or butterhead, 4"- 10" in-row x 12"- 24" between rows; crisphead, 12"- 15" in-row x 20"- 30" between rows. Initial and eventual spacing (after thinning)depends on inteneded harvesting stage.
  • Fertilizer needs
  • Approximate yield: 2 - 10 lbs. per 10-foot row (depends greatly on lettuce type).
  • Lettuce problem:

Types of Lettuce

  • Leaf 

    Most gardeners raise this type, either with green or reddish leaves. Fast-growing and long-lasting, this type can be grown from March to December with a break in July and August. Sow 10 to 20 seeds per foot of row. Thin individual plants 4- to 8-inches apart, depending on variety. Leaf lettuce also grows very successfully in a wide-bed arrangement when seedlings are thinned to 4- to 8-inches on all sides.

  • Butterhead

    Bibb and Boston are examples of this loose-heading type with dark green leaves that are somewhat thicker than those of iceberg lettuce. Butterheads develop a light yellow, buttery appearance. Small-headed varieties are good choices for succession plantings. It may be started indoors for an even longer season. Bibb lettuce becomes bitter under high summer temperatures.

  • Romaine or cos

    Is typically less commonly grown by gardeners, but a very nutritious lettuce that deserves attention. Relatively easy to grow, forms upright heads with wavy, attractive leaves.

  • Crisphead (iceberg)

    It has a tightly compacted head with crisp, light green leaves. Many gardeners find this type difficult to grow because it requires a long, cool season and goes to seed as soon as temperatures rise. Select a slow-bolting variety and start seed indoors in late winter for late spring/early summer harvest, or late summer for fall harvest. 

  • Escarole, endive, and chicory

          All three are treated much the same as lettuces. Follow seed packet instructions.

Growing and Care of Lettuce

  • Lettuce is an easy-to-grow, cool-season crop that can withstand light frost.
  • It is best planted in succession or using different varieties that mature at different times for a longer harvesting period. 
  • 3 to 4 week old transplants can produce earlier harvests, eliminate the need for thinning, and increase garden productivity.
  • Increasing day-length and high summer temperatures usually cause seedstalk formation (bolting) and bitter flavor. Slow-bolting or heat-resistant varieties (e.g., oak-leaf types) are available and are recommended for extending the lettuce-growing season. 
  • Plant early spring lettuce in full sun or soil that will be warm enough for rapid growth. Plant long-season lettuces so that crops such as sweet corn, staked tomatoes, pole beans, or deciduous trees will shade the lettuce during the hottest part of the day. Interplanting or planting between rows or within the row of later- maturing crops like tomatoes, broccoli, and Brussels sprouts is a space-saving practice.
  • Some lettuces are very attractive and can be grown in flower borders.
  • Lettuce grows well in containers, Salad Tables™, and Salad Boxes.
  • Weeding - Cultivate carefully, as lettuce is shallow-rooted. Organic mulches are helpful in conserving soil moisture, maintaining even soil temperatures, and limiting weed growth.
  • Watering - Use frequent, light watering to encourage rapid growth. But, do not over-water, as this may contribute to root and leaf diseases. Overhead watering should always be done in the morning to give plants time to dry off during the day.

    salad table full of lettuce
    Growing lettuce in a salad table

Extending the Lettuce Growing Season

  • Plant successive lettuce crops in spring and use tall crops and trellises to protect the late spring lettuce plantings from direct aftrenoon sun. 
  • Interplanting – planting between rows or within the row of later-maturing crops like tomatoes, broccoli, and brussels sprouts – is a space-saving practice.  
  • Floating row covers are very useful in promoting rapid growth in the early spring and minimizing slug and other pest feeding.
  • Lettuce production can be also extended later in the fall with floating row covers or cold frames. 
  • Some lettuce cultivars may overwinter if healthy three-week-old transplants are planted around October 15.  These small plants will establish a root system and be able to withstand cold weather with protection. When spring arrives they will begin active growth and produce early harvests. 
  • Some recommended cultivars for overwintering include Black Seeded Simpson, Waldmann’s Dark Green, Salad Bowl, Winter Density, Brune D’Hiver, Winter Marvel, and Arctic King. 

Harvesting Lettuce

  • Leaf lettuce can be used as soon as plants are 5 to 6 inches tall. Use the older, outer leaves which contain high levels of calcium first. You may wish to harvest every other one of the largest plants to accomplish thinning.
  • Bibb lettuce is mature when the leaves begin to cup inward to form a loose head.
  • Romaine or cos is ready to use when the leaves have elongated and overlapped to form a fairly tight head about 4 inches wide at the base and 6 to 8 inches tall.
  • Crisphead is mature when leaves overlap to form a compact and firm head.
  • Cut and Come Again Harvesting: For continuous harvests of quick and easy salad greens. Sow a raised bed thickly with a mixture of your favorite salad greens (with maturity dates close to one another). Cut plants right above ground level with sharp scissors when they are 6 to 10 inches tall. They will quickly re-grow if watered and fertilized and be ready to cut a second time 2-3 weeks later. Sow a second bed. Turn under the plants when they become overly-mature and bitter. 

Storage and Preservation  

  • Very cool (32 degrees F), moist (95% RH) conditions; 2-3 weeks.  Crisphead lettuce will keep about two weeks in the refrigerator. Leaf and Bibb will store as long as four weeks if the leaves are dry when bagged. If lettuce is to be stored, harvest when dry, remove outer leaves but do not wash, place in a mesh or plastic bag, and store in the crisper drawer.

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