Lettuce is one of the most widely eaten vegetables in the world. These leafy greens are cultivated from North America to Europe and Asia, but lettuce is also one of the easiest vegetables to start in a home garden. Although many countries grow and export lettuce, nearly all of the salad greens in your grocery store were harvested from U.S. farms.
Lettuce is considered to be one of the simplest short-season, cool-weather crops to grow. Lettuce doesn’t require a high-level of maintenance, and gardeners tend to favor this crop since it is so reliable in its production. Being that it is a cool-season crop, lettuce is generally tolerant to light frost, but becomes susceptible to bolting in too high of temperatures.
Lettuce is able to be grown in a variety of states and countries since it is highly adaptable to many climates, and different varieties are more heat tolerant than others.
What States Grow Lettuce?
When it comes to U.S. lettuce, the state of California reigns supreme! In 2007 California grew 74% of our total lettuce, with farms stretching from the central coast all the way to its southern deserts.
Lettuce production is highest in Monterey, along California’s central coast. This region has famously mild winters; lettuce is harvested here from April all the way to November. Iceberg is still most popular, followed by romaine and leaf lettuce.
Arizona comes in second producing 25% of our total lettuce. This state might conjure images of sand and tumbleweeds, but the desert southwest has one of the longest growing seasons in the United States. Arizona’s warm winters are particularly ideal for lettuce.
In fact, if you buy any lettuce between November and March, thank Arizona growers! Over 90% of the United States’ winter lettuce comes from Arizona’s Yuma Valley. Most is iceberg and romaine, but the Yuma region also gives us spinach, leaf lettuce, and baby greens.
Other states that grow lettuce are Oregon, Mississippi, Maryland, and North Carolina. Both leaf and head lettuce grow successfully in Mississippi climates, and tend to be planted in the late Winter or early Spring.
In Oregon, leaf lettuce grows best in temperatures from 60 to 70 degrees, and tends to be planted in early Spring for a summer harvest, and in the late summer for harvest in the Fall.
In Maryland, leaf lettuce is grown from March to December with a break in July and August, considering those are the hottest months in the year.
In North Carolina, for example, lettuce can be grown as a spring and fall crop in eastern parts of the state, and during the summer in midwestern parts of the states.
What Countries Grow Lettuce?
China is far and away the world’s largest lettuce grower. China’s lettuce production in 2004 was a whopping 23 billion pounds. By contrast the U.S., although second worldwide, grew less than half this quantity (9.7 billion pounds).
Chinese lettuce is mostly stem-type, which sprouts leaves from a thick lower stem. Much of China grown lettuce is consumed domestically, meaning China actually exports less lettuce than the U.S. worldwide.
Globally, the U.S. is also second in terms of lettuce exports. Spain ships the most lettuce: over a third of the world’s total exports. Other big European lettuce exporters include Italy, Belgium, and the Netherlands.
Almost all the lettuce we eat in the United States comes from U.S. farms. Between 2005 and 2007, only 2% of the lettuce sold here was imported from neighboring Mexico and Canada. Most of this was specialty hydroponic lettuce from Canada.
The big reason for this is our country’s continuous production. Thanks to farms in California and Arizona, the U.S. can grow its own lettuce year-round. This eliminates the need for imports during the winter, for example.
Where Does Lettuce Come From?
Some sources claim lettuce originated in the Middle East; other sources say North Africa. However, most of our modern lettuces came from the Mediterranean region. It was domesticated here between 4000-8000 BCE, making lettuce one of the oldest cultivated vegetables.
Egypt has the earliest known records of lettuce. The ancient Egyptians domesticated “prickly” lettuce for forage and for its seeds’ oil. In fact, certain tombs in the Nile region were even decorated with artwork of what resembles romaine.
Lettuce soon spread from Egypt to Greece, where it became a popular vegetable crop. By 850 BCE leafy greens had developed a healing reputation. The Greek physician Hippocrates believed the milky sap from lettuce leaves could induce sleep and relieve pain.
Lettuce’s medicinal qualities are the origin of our modern salads. The Greeks ate lettuce coated in oil as a pre-meal dish, a custom adopted by the Romans. The Romans would later introduce lettuces to Europe.
During the medieval period, Europeans farmed a diverse variety of leafy greens. Romaine was probably first cultivated in Italy, while head lettuce appeared for the first time in the 16th century. Columbus’s second voyage in 1494 brought domesticated lettuce to the Americas.
Between 1850-1900, scientists in Europe and America made big leaps in lettuce quality. Careful breeding led to better leaf texture, better head formation, and less bitterness. This turned wild lettuce into something you might see at your grocery store.
Of course, crop scientists are still tinkering with lettuce today! Recent breeding has focused on everything from disease resistance to improving shelf life. Certain programs are dedicated to breeding low-nitrate lettuce, given the health concerns around nitrate consumption.
Where Does Lettuce Grow Best?
Lettuce is generally a cool-season crop, but each variety has subtle differences. The U.S. grows four major types of lettuce: crisphead, romaine, leaf, and butterhead.
Out of these four, crispheads like iceberg are the most picky. Iceberg lettuce prefers day temperatures around 73F and nighttime lows around 45F. Hotter weather will cause the lettuce heads to fail, while hard freezes will damage outer leaves.
Iceberg matures more slowly than other types, so it’s in danger of early bolting from stress. This lettuce likes to grow in mild climates without temperature extremes. For these reasons, iceberg grows best during the winters of California and Arizona.
Leaf, romaine, and butterhead lettuces all have temperature needs similar to iceberg’s. However, these types do mature faster than crisphead lettuce, so they can succeed in a warmer growing region.
Leaf and butterhead lettuces tolerate other poor conditions, like sandy soil, since this helps their shallow roots with drainage. As long as these roots stay cool and well-watered, leafy greens will thrive in the desertlike conditions of Spain, Italy, and the American Southwest.