ten
FACTS ON
LETTUCE
1 Although there are many varieties, all lettuces grown for
food are members of the species Lactuca sativa.
by Philip McIntosh 2 The genus name Lactuca comes from Latin, meaning
“milky sap,” and the specific epithet sativa means “cultivated.”
Popular the world over,
lettuce, in all its varieties,
is one of most
common plants seen in
hydroponic culture. 3 Although perhaps not the oldest plant in cultivation,
4 Flowers are not desirable on a lettuce plant destined for
5 Many plants possess a milky latex (Euphorbias and
milkweeds for example) but there are few edible latex producers,
Lactuca sativa being an important exception.
6 Some sources group lettuce cultivars into five groups,
7
lettuce does go way back, all the way to ancient Egypt (at least),
where it was considered useful for enhancing sexual performance
(unlikely), as well as for medicinal, ritual, and culinary purposes.
the table, but if allowed to flower, it is clear that all 50 or so members
of the genus are Asteraceae (in the aster, or sunflower family).
but the four main ones are: iceberg (large, tight, firm heads); bib
(a smaller tight head with looser leaves all around); cos (elongated
spoon-shaped leaves as seen with romaine); and, loose leaf
(narrow leaved and straggly looking without a well-developed head).
Known as a cool weather species, lettuce does best if
temperatures are kept between 45–80°F.
8 Lettuce will bolt (rapidly go into flowering phase) and
9 Experiments done by the U.S. Department of
Agriculture suggest that long days are more stimulating to
become bitter when exposed to a combination of high temperature
and long day length.
flowering than high temperatures, making lettuce more difficult to
grow during the summer, even in cooler climates.
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74
Maximum Yield
A combination of shading and cooling of the nutrient
solution has allowed lettuce to be grown indoors or in greenhouses
year round, even in warm climates.