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University
of Rhode Island GreenShare Factsheets
Lettuce
Lettuce varieties can be loosely categorized into four groups:
crisphead, butterhead, leaf and romaine or cos. Each group has
its own growth and taste characteristics.
Crisphead lettuce is probably the most familiar of
the four. It is characterized by a tight, firm head of crisp,
light-green leaves. Crisphead lettuce is generally intolerant
of hot weather and will readily bolt or send up a flower stalk
under hot summer conditions. Its long growing period also makes
it one of the most difficult of the lettuces to grow in New England.
The butterhead types have smaller, softer heads of
loosely folded leaves. The outer leaves may be green or brownish
with cream or butter colored inner leaves.
Leaf lettuce has an open growth and does not form
a head. Leaf form and color varies considerably--some cultivars
are frilled and crinkled and others deeply lobed. Color ranges
from light green to red and bronze. Leaf lettuce matures quickly
and is the easiest to grow.
Romaine or cos lettuces form upright, cylindrical
heads of tightly folded leaves. The plants may reach up to 10
inches in height. The outer leaves are medium green with greenish
white inner leaves. Romaine is the sweetest of the four types.
Lettuce is a cool-season vegetable and develops best quality
when grown under cool, moist conditions. Lettuce seedlings will
tolerate a light frost. Temperatures between 45 F and 65 F are
ideal. Seeds of leaf lettuce are usually planted in the spring
as soon as the ground can be worked. Butterhead and romaine can
be grown either from seeds or transplants. Due to its long-growing
season, crisphead lettuce is grown from transplants. Transplants
may be purchased or started indoors about six weeks before the
preferred planting date.
Lettuce can be grown in a wide range of soils. Loose, fertile,
sandy loam soils, well-supplied with organic matter, are best.
The soil should be well-drained and moist but not soggy. Heavy
soils can be modified with well-rotted manure or compost, or
by growing a cover crop. Like most other garden vegetables, lettuce
prefers a slightly acidic pH of 6.0 to 6.5.
Since lettuce seed is very small, a well-prepared seedbed
is essential. Large clods will not allow proper seed-to-soil
contact, reducing germination. Lettuce does not have an extensive
root system, making an adequate supply of moisture and nutrients
also necessary for proper development.
Fertilizer and lime recommendations should be based on the
results of a soil test. As a general
rule, however, apply three to four pounds of 5-10-10 fertilizer
per 100 square feet of garden area.
Seed may be sown in single rows or broadcast for wide row
planting. Wide rows should be 12 to 15 inches across. Cover the
seeds with 1/4 to 1/2 inch of soil. Water carefully but thoroughly.
Several successive plantings of leaf lettuce will provide a more
continuous harvest throughout the growing season. Leave 18 inches
between the rows for leaf lettuce and 24 inches for the other
types. To achieve proper spacing of plants, thinning of lettuce
seedlings is usually necessary. Thin plants of leaf lettuce four
to six inches or more between plants, depending on plant size.
Butterhead and romaine should be thinned six to ten inches between
plants. Crisphead transplants should be spaced 10 to 12 inches
apart in the row.
An organic mulch will help conserve moisture, suppress weeds
and keep soil temperatures cool. If weeds become a problem, pull
by hand or cultivate very shallowly to avoid damage to lettuce
roots. Planning your garden so that lettuce will be in the shade
of taller plants in the heat of the summer may reduce bolting.
All lettuce types should be harvested when they have reached
full size but are still young and tender. Over-mature lettuce
is bitter and woody. Leaf lettuce is harvested by removing individual
outer leaves, leaving the center leaves to continue to grow.
Butterhead or romaine types can be harvested by removing the
outer leaves, digging up the whole plant or cutting the plant
about an inch above the soil surface, usually allowing for a
second harvest. Crisphead lettuce is picked when the center is
firm.
Adapted from Marianne Riofrio,
Ohio State University Extension, 2000
Pesticides
are poisonous! Read and follow all safety precautions on labels.
Handle carefully and store in original containers out of reach
of children, pets or livestock. Dispose of empty containers
immediately, in a safe manner and place. Pesticides should never
be stored with foods or in areas where people eat.
When trade names are used for identification, no product endorsement
is implied, nor is discrimination intended against similar materials.
Be sure that the pesticide you intend to use is registered for
the state of use.
The user of this information assumes all risk for personal injury
or property damage.
For more
information, call the URI CE Gardening and Food Safety Hotline
at 1-800-448-1011 or (401)874-2929 from outside Rhode Island;
Monday-Thursday between 9 am and 2 pm.
University
of Rhode Island Cooperative Extension provides equal program
opportunities.
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