Lettuce
– the king of salad vegetables – rules in 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.
History
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 61 beds he mapped out for his near-acre plot,
16 were planted with lettuce.
In 1806, a seedsman of the times, McMahon, listed 16 varieties of lettuce in
his catalogue. Le Bon Jardinier of 1880 lists 40 varieties existing in France. A
report of the New York Agricultural Experiment Station of 1885 describes 87
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 by far the most widely consumed form in the
United States, accounting for 95 percent of all lettuce produced and sold
commercially here. 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 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 flavour where they are a major ingredient in Caesar salad.
Lettuce Culture
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, in planter boxes, or in 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 10 to 14 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.
Soil Requirements
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 provide 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 flavour 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.
Seed Sowing
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. Or fool mother nature by using the refrigerator technique.
The refrigerator technique consists of mixing two or three dozen seeds in a
cup of dampened sphagnum moss, storing the moss and seeds in a plastic bag in
the refrigerator during the day, and removing them at night. The alternation of
heat and cold will start seeds sprouting in a few days. When the first seeds
sprout plant them along with the moss, in a prepared bed and cover lightly with
sand. This should be done on a cool gray day, or in late evening, and the bed
should be watered well. Then, as in all other lettuce growing, the bed should be
kept moist.
Regardless of how or when lettuce seeds are sown, they should get a 1/4-inch
noncrusting covering during the cooler months, and a 1/2-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 6 to 12 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 1/2 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.
Pests
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.
Common
Problems
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.
Prepared with the assistance of the National Garden Bureau.
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