Lettuce is a cool weather crop, so it’s perfect for growing in spring or fall. Here is everything you ever wanted to know about growing lettuce.
By Wendy Priesnitz
Lettuce – the king of salad vegetables – is part of the meals of people throughout the world. It is by far the most widely used salad crop in North America, and is also important in Australia and most countries in Europe and South America. Its popularity is increasing in Africa, the Middle East and Japan. Indeed, the importance of lettuce is established in nearly every cuisine around the world.
Lettuce (Lactuca sativa) has been cultivated for ages, possibly longer than any other common vegetable crop. Pictures of a pointed-leaved lettuce have been found in Egyptian tombs dating back to 4500 B.C. (Historical botanists think, however, that the Egyptians grew lettuce for the edible oil extracted from its seeds.) Herodotus spoke of lettuce being served at the royal table of Persian kings in the fifth century B.C.; Theophrastus named three varieties in his History of Plants, 350 B.C. In the year 1 A.D. the Romans mentioned 12 lettuce varieties. In ancient Rome, lettuce was a luxury crop for the wealthy and reserved for feast days.
Lettuce has been grown not only as a food but as a medicinal herb. Its milky juice is recommended in The Herbal as a sedative. In Germany, Lactuca vurisa, a close lettuce relative, was used to induce sleep. Elizabethan herbalists commented on the importance of lettuce and recommended that it be eaten at mealtime and before “indulgence in drink” – because, one of them wrote, “it staieth the vapours that disturb the head and cooleth the hot stomache which some call heart burn.”
Garden lettuce has been cultivated so long that its origin is uncertain. So far, it has not been found in the wild. Plant geographers and historians hold that its precursors originated in the Mediterranean area, possibly Egypt, and that its seeds were carried throughout the world by travelers, explorers and conquerors. Charlemagne’s historians credit him with bringing lettuce into France in 780 A.D.
Lettuce seeds were apparently first brought to the New World by Columbus, for it is recorded as being cultivated at lsabela, his first stop, in 1494. Dutch and English settlers brought lettuce to the northern part of America and it came with the French explorers to Canada.
By colonial times lettuce was a common vegetable in the gardens of upperclass families, if one can judge from the working kitchen garden planned by George Washington at Mt. Vernon. Of the sixty-one beds he mapped out for his near-acre plot, sixteen were planted with lettuce.
In 1806, a seedsman of the times, McMahon, listed sixteen varieties of lettuce in his catalogue. Le Bon Jardinier of 1880 lists forty varieties existing in France. A report of the New York Agricultural Experiment Station of 1885 describes eighty-seven varieties with 585 names of synonyms.
Garden Lettuce Types
Horticulturally, lettuce is categorized by most authorities into four groups based on growth habit. The groups are: head, semiheading, looseleaf and cos or Romaine.
1) Crisphead or head lettuce is the most popular type in North America. This is the type normally purchased from the produce department where it is often sold as “iceberg,” which is actually only one of several varieties of head lettuce.
2) Semi-heading lettuce is also called butterhead, or sometimes Boston or Bibb. In this form, the outer leaves do not wrap tightly together; instead, they develop an open, fairly flat rosette surrounding the inner leaves that barely overlap, forming blanched hearts. The broad oval leaves are soft and pliable and are usually greener and some consider more tasty than crisphead types. Butterhead types are a natural choice for home gardeners because their culture is not too demanding; and because they do not hold up well during shipment, they are seldom found in satisfactory condition at produce stands. Butterhead cultivars are widely planted by Europeans.
3) Most gardeners are familiar with looseleaf lettuce, regarded by many as the easiest to grow. Here the leaves grow up and out forming a loose rosette. This form is sometimes referred to simply as leaf lettuce or as curled lettuce. The looseleaf types considerably broaden the gardener’s palette because they supply a wealth of delicious leaves in different colours, textures and leaf shapes.
4) Cos (derived from the Greek island Kos) or Romaine (showing its Roman heritage) develops a distinctly upright, cylindrical head as opposed to the rounded form of crisphead. The inner leaves of cos become blanched naturally in the development of the head and are used for their crispiness and especially piquant flavor where they are a major ingredient in Caesar salad.
If one is planting a vegetable garden for the first time, lettuce would be a good beginning crop. Seeds sprout quickly in cool soil and plants grow rapidly. Lettuce plants can be transplanted and tucked into sunny open spots in the vegetable or flower garden, and make a good addition to planter boxes or hanging baskets. A large plot is not needed to grow lettuce; in fact, nearly all varieties are small enough to be grown in confined areas such as a patio, balcony, or courtyard garden.
A large planting of lettuce is usually unwise for the home gardener and while it can be refrigerated, its quality does not improve in storage. Experienced gardeners have found that at any one time a five to eight foot row of lettuce, preferably a mixture of varieties, is enough for a family of four. One of the keys to successful home garden production is sowing small amounts of lettuce seed every ten to fourteen days, except just prior to the heat of the summer.
A Cool-Weather Crop
Lettuce seedlings are hardy and can withstand light frosts. Seeds are customarily sown in early spring and again in early fall, except in the northern parts of North America, coastal fog belts, and cool mountain gardens where summer plantings can also be made. Summer plantings in other areas quickly shoot up flower heads (known as “bolting”) because, as the days grow longer and hotter, the reproductive system is set into action. Temperatures in the mid to upper 80 degrees F (20 degrees C) will trigger this bolting action. With the development of the seed stalk, lettuce leaves become bitter and tough, so the aim is to have a lettuce crop ready to harvest before or after the heat of summer. If mid-summer culture is attempted, choose a location with filtered shade all day or full shade from mid-afternoon on.
Succession plantings, the use of cold frames, cloches, and other protective devices, as well as utilizing cold-resistant varieties, all help to make extended-season lettuce a practical goal in the home garden.
Provided climatic requirements – especially temperatures – are met, lettuce grows successfully on a wide variety of soil types ranging from mucks, sandy loams, to clay or clay loams. It is a shallow-rooted crop that needs both good drainage and a steady supply of water. Abundant organic matter blended into garden soil helps service these needs. Because of the shallow root system, deep cultivation should be avoided.
Feeding and Watering
Lettuce is a moderately heavy feeder and usually responds dramatically to the application of fertilizer or compost. Average garden soils should be fertilized to produce a superior quality of lettuce. An application of organic fertilizer or compost should be blended into the soil prior to seed or setting out transplants. A second application should be applied in bands on both sides of the row when the lettuce plants reach a height of two to three inches. This application, called a side-dressing, should be lightly cultivated into the soil and followed by a thorough irrigation. In most garden soils the sidedressing can be a fertilizer containing just nitrogen, such as ammonium sulfate or ammonium nitrate.
As with other crops, the question of fertilizing lettuce boils down to no single correct answer for every situation. In garden soils that have been generously fortified with well-rotted manure or a rich compost, addition of fertilizer may not be necessary.
Soil pH should be in the range of 6.0 to 6.5. This assures availability of nutrients from the soil.
To keep lettuce growing rapidly and to develop the very best flavor, it should receive about an inch of water weekly. The very best lettuce is that which has grown quickly. This is assured by adequate fertilizing, steady water supply, and cool temperature.
To get an autumn crop where severe cold weather comes early, seed sowing may need to be advanced to late July or August when soil temperatures are not conducive to best germination. For mid-summer sowings, choose a spot in the cool, filtered shade of other crops such as pole beans or tomatoes and keep the seedbed moist to take advantage of evaporative cooling. Another approach is covering the seedbed with a layer of burlap kept moist. Be sure to remove it when the first seeds sprout.
Regardless of how or when lettuce seeds are sown, they should get a quarter-inch non-crusting covering during the cooler months, and a half-inch covering during the warmer months. Always keep the seedbed uniformly moist. In warm, sunny weather this may require watering once or twice each day.
Succession Planting and Transplants
By starting a new crop of lettuce every two or three weeks, one will always, in successive crops, have the making of a fresh, bright, crisp addition to any meal. Generally, the first crisphead and butterhead plants are started indoors four to six weeks and loosehead types two to three weeks, before the last average frost. This early planting not only extends the lettuce growing season, it produces young plants ready for the garden at a time ideal for lettuce growth. When the seedlings have two or three true leaves, they are transplanted, two inches apart in flats or other shallow containers. They can also be planted individually into peat pellets or to 2-1/4-inch peat pots. When the leaves start touching, the flats can be placed outside during the warm time of each day, or carried in a coldframe until the outdoor bed has warmed up enough to receive the transplants.
A well hardened-off plant, that is, a plant that has been exposed gradually to outdoor conditions, will adjust quickly after being transplanted to the garden. Do not allow lettuce transplants to become dry and overgrown because they do not recover readily. The young plants should be spaced six to twelve inches apart in the garden, depending on the variety; crispheads need the most room.
The first outdoor sowing can usually be made at the same time the young plants are set out. When sowing directly, sow seeds about a half inch apart either in rows or in wide bands. Remember that surplus seedlings should be removed while small; either to another row, tucked between other plants, or for an early salad. Thin out surplus seedlings by the time they develop two to three leaves.
Transplanted seedlings will mature about 10 days later than the original sowing. This delay adds to the succession process. As the plants enlarge, it is a common practice to harvest every other one as needed, thus giving those remaining more growing room.
Lettuce is susceptible to a few pests that can be real nuisances in the home garden. Slugs and snails can wreak havoc overnight, especially when seedlings are young and tender. Hand picking and clean garden practices are the first line of defense.
Birds can decimate a lettuce patch, and they like the same tender seedlings as do the slugs. One remedy is to cover small plants with mesh or wire; another is to start plants indoors and not transplant them until they are past the attractive stage (from the bird’s point of view).
Aphids, white flies, and leafhoppers sometimes become lettuce pests, not only for the damage they do to the plants, but also for the crippling plant virus diseases they carry. Sometimes aphids can be washed off with a stiff spray of water, or use a homemade garlic spray. Ladybugs and lacewings eat these pests, so encourage them in your garden.
Cabbage looper worms and other larvae can be destructive, but often there isn’t a big enough infestation to require anything but hand picking. For these chewing pests there are safe biological controls if your garden becomes overrun.
Seeds didn’t come up: Check for these causes: old seed, soil too warm, seedbed dried out, seeds covered too deeply, birds or other pests.
Plants went to seed before much was harvested: It is natural for lettuce to bolt (go to seed, causing an elongation of the core) during long days and warm temperatures. There are two approaches to this problem. Choose “slow-to-bolt” varieties. Genetic factors in these types keep them producing vegetative growth for a longer time during summer. Eventually, even they will bolt. Or make successive sowings, keep the plants cool, and harvest early.
Leaves were bitter: This is mostly caused by delaying harvest too long. Pick lettuce at its tender, tasty prime and keep succession plantings coming along. Bitterness can be brought on by slow growth due to poor growing conditions such as inadequate water or fertilizer. Temperatures in the 80s or above also cause bitterness. To a limited extent, bitterness is a genetic factor. Try several different varieties and discover some that are more suited to your taste than others.