What is Lettuce, You Ask? | UC Agriculture and Natural Resources

October 14th, 2024

Stanislaus

Green container holding two types of lettuce mentioned in the article. — Lettuce growing in a container.

Lettuce is a leafy annual green, almost exclusively eaten raw. There are four main types of lettuce: romaine (or cos), which forms tall and loose oblong heads; crisphead, which grows in tight heads that resemble cabbage; butterhead, which grows in soft, thick-leaved heads; and looseleaf, or leaf lettuce, which grows in a loose rosette of tender leaves off the stem. Within these four varieties, there are more than enough subvarieties to try a new one every day of the month.

Romaine Lettuce

One of the most popular lettuces in the country, romaine lettuce is crispy and fresh and perfectly mild.

Crisphead Lettuce

Iceberg lettuce is the most common crisphead lettuce variety. Look quickly, and you might mistake it for a green cabbage.

Green and Red Leaf Lettuce

Leaf lettuce grows with leaves that branch from a single stalk loosely rather than forming a tight head. It's got thinner, more tender leaves that ruffle and frill in gorgeous ways. The taste of green and red leaf lettuce is quite similar: a little bit pleasantly earthy and totally refreshing.

Butter Lettuce

Butter lettuce, which includes Bibb and Boston lettuces, have tender leaves with a very mild, buttery flavor making it an excellent addition to salads and sandwiches. Butter lettuce is known for its small, round, loosely formed heads with soft, buttery-textured leaves.

For best results, lettuce should be started indoors. If you do not have access to a greenhouse, lettuce can be started in a flat, atop a simple heat mat, or in a warm spot in your home. Lettuces, although some are cold hardy, will still germinate best when temperatures are above 35 degrees°F. Lettuce is generally a cool weather crop that grows best at 60-65°F. It should be expected to germinate best at temperatures below 70°F.

Although they are considered a cool season crop, it should be noted that there are varieties available that are more heat tolerant and can do well even in 90-100 degree temperatures. Two such varieties I have found are ‘Nevada Green' and ‘Cherokee Red.'

These plants are still going strong even though here we have been experiencing a huge number of triple digit temperature days over the last 2 months.

How to grow lettuce

Hand showing how small lettuce seeds are next to a penny. — Lettuce seeds.

Lettuce prefers fertile, well-drained soils rich in organic matter for best growth.

Before planting, determine fertilizer needs with a soil test. work the fertilizer into the top 6 inches of soil. If you fertilize with compost, apply no more than 1 inch of well-composted organic matter per 100 square feet of garden area.

Lettuce seeds are very small and should not be planted too deep. They should be kept moist but not saturated to properly germinate.

Lettuce can be grown from seed or transplants. Seeds should be planted ¼-½ inch deep and thinned when plants have 3-4 true leaves. Plants removed at thinning can be transplanted to adjacent areas if some roots are maintained. Thinned plants can also be eaten. Transplants provide an earlier harvest. Transplants should have 4-6 mature leaves and a well-developed root system before planting out. Generally, 5-6 weeks are required to grow transplants to this size.

Seeded or transplanted lettuce should be spaced 8-12 inches between plants in the row with 12-18 inches between rows in a location that will receive full sunlight. Dense plantings will reduce weed pressure. Lettuce grows best when temperatures do not exceed 75 degrees F. Temperatures down to 32 degrees F do not seriously damage young plants. Transplants should be planted near the last frost-free date for the growing area. Seeded lettuce may be planted 2-3 weeks earlier. High summer temperatures reduce growth, decrease quality, and cause bitter or off flavors to develop. For fall lettuce, select early maturing cultivars and plant 50-75 days before the anticipated maturity date. The maturity date should be about 1-2 weeks before the first fall frost. Plants can be left in the garden after light frosts.

Water lettuce regularly supplying 1-2 inches per week. Water requirements depend on soil type and temperatures. Use drip irrigation, if possible, to conserve water. A mulch around the plant also helps conserve soil moisture and reduce weed growth. Moisture fluctuations will cause leaves to become tough, slow head development and contribute to off flavors. Wet and dry periods favor the development of tip burn, a browning of the edge of some of the internal leaves.

Apply ¼ cup of a nitrogen-based fertilizer (21-0-0) per 10 foot of row (or according to packing instructions) 4 weeks after transplanting or at thinning to encourage rapid plant growth. Place the fertilizer to the side of the plants and irrigate it into the soil.

Plastic mulches help conserve water, reduce weeding and allow for very early maturity, especially with transplants. Fabric covers are used to protect seedlings and transplants from frost. Apply organic mulches such as grass clippings, straw, and newspapers to cool the soil when temperatures increase, reduce water stress, and help control weeds.

Leaf lettuce is considered a cut & come again plant, meaning you can remove outer leaves as you need them for consumption or cut off the entire top leaving at least an inch or two which will then regrow for you.

So, enjoy your lettuce in your salads or sandwiches and keep on gardening!