Each year, the United States grows more than 4 million metric tons of lettuce. It’s been a part of our diet since Christopher Columbus introduced it to the New World, was a favorite in Colonial times and remains the country’s leading fresh vegetable crop today, with each of us consuming approximately 36 pounds of it per year.
It’s no wonder, really, that this leafy vegetable is so popular. It’s full of antioxidants and vitamin K, contains plenty of vitamins A and C (especially in darker-colored varieties), and is a good source of folate. Plus, it’s tasty, doesn’t require cooking—though many cooks around the world do so—and is easy to grow. There’s one more surprising attribute to add to the list of reasons for its popularity: Many lettuces also contain lactucarium—commonly known as lettuce-opium—a mild analgesic and sedative that can generate a weak opium-like sense of euphoria. The milky latex sap of lettuce was (and still is) harvested, reduced and used in lozenges and tinctures as a sleep aid and natural pain reliever. Even though the compound isn’t actually a drug or narcotic of any sort, many say you can obtain a “lettuce high” simply by eating a big salad.
Although feeling a post-salad sense of euphoria shouldn’t be your main reason for consuming lettuce, wanting to eat more of it certainly isn’t a bad thing. It’s good for you, after all, and lettuce’s ease of growth makes it one vegetable that even beginners can grow in abundance.
Pick Your Lettuce Variety
Most large-scale commercial lettuce production takes place in Arizona and California, but small-scale farmers across the country can reap the benefits of lettuce’s popularity by growing for farmers’ markets, farm stands, specialty markets and restaurant chefs.
Commercial production focuses largely on a small handful of varieties that are uniform in growth, have a decent shelf life and are shippable, but hobby farmers have far more extensive choices. According to a report by the Agricultural Marketing Research Center at the University of California, iceberg lettuce remains the most popular type, though its ranking is slowly falling as the popularity of romaine and leaf lettuces rises. With the increase in packaged lettuce mixes, small-scale farmers can turn a profit on colorful salad mixes and unusual varieties that are often more nutrient-dense than iceberg and are more appealing within today’s “buy local” movement.
Lettuce is generally categorized into five distinct groups:
- Romaine or cos lettuce varieties form an upright, elongated head. (Think Caesar salad.)
- Loose-leaf or leaf types have leaves of various shapes loosely arranged around the stem.
- Crisphead lettuces form a dense, compact head surrounded by a few looser leaves. (Iceberg fits in this category.)
- Butterhead (also commonly called Bibb, Boston or Buttercrunch) varieties form very loose heads of tender, sweetly flavored leaves.
- Stem lettuce varieties have elongated leaves with a very bitter flavor and are commonly used in Chinese cuisine.
The key to growing lettuce is to diversify.
“There are so many different varieties and colors and textures, and such a difference in flavor profiles amongst varieties,” says Josh Kirschenbaum, head of product development for Territorial Seed Company in Cottage Grove, Ore. “You would be doing yourself a great injustice if you only grew one type.”
“And along with the different colors, come different nutritional values,” he says, adding that “we eat with our eyes first,” so bringing diversity to the salad plate is a beautiful thing for many reasons.
Plant Lettuce Seeds
No matter what type (or types) of lettuce you decide to grow, a few simple steps will encourage your success. First and foremost, understand that lettuce is a cool-season crop and grows best when daytime temperatures are between 60 and 70 degrees F. In Oregon, that means Kirschenbaum is planting lettuce from early to late spring and then again at the beginning of fall. Linda Lehmusvirta, producer of Central Texas Gardener for PBS affiliate KLRU-TV, grows her lettuce throughout the winter, planting from September to mid-March.
Wherever you live, plan to plant lettuce when the temperatures are appropriate for the longest period of time. Most lettuce varieties need 30 to 50 days to reach maturity, so plan accordingly.
Lettuce dislikes heat and will bolt (i.e., go to flower) when temperatures rise and days lengthen. Gardeners in the extreme North can sometimes get away with growing lettuce in the summer months, but for most of the country, spring and fall are the most fitting. Position lettuce where it receives a minimum of six hours of direct sun (though summer-grown crops tolerate, and might even prefer, full shade) and amend the soil with plenty of organic matter. Lettuce grows best with a soil pH of 6.0 to 6.5. Test your soil every few years and adjust it accordingly.
There are two primary ways to get your lettuce crop started: direct-seeding outdoors or sowing seeds indoors under grow lights. Direct-seeding lettuce into the garden is less time-consuming and doesn’t require any special equipment. Seeds are sown according to package instructions when soil temperatures range from 40 to 70 degrees F. The disadvantages to direct-seeding are an increased risk of loss due to weather conditions, the overuse of seed (i.e., sowing too thickly) and the need to thin the resulting seedlings.
Many gardeners prefer to direct-sow lettuce seeds they plan to harvest in the “baby” stage, as young, undeveloped greens. Meant to serve as a “cut-and-come-again” salad, seeds can be intentionally sown thicker because full-sized heads will never develop.
Starting seeds indoors is also beneficial to many gardeners. The farmers at Cure Organic Farm in Boulder, Colo., have found that starting seeds in a greenhouse yields higher germination rates than direct-seeding. And because the resulting transplants are spaced properly in the garden, Kirschenbaum adds, it’s less wasteful, especially for varieties grown to maturity.
“The seed is very small and there are about 25,000 seeds per ounce and so if I direct sow, I’m going to have to thin and there will be dense patches and empty patches. I have more control over those issues by starting them indoors,” he says. “Starting the seeds is easy because you don’t have to keep them warm for good germination, so there is no need for heating mats. Nor is there a need to transplant them into larger containers. I start them in a 72-cell flat and try to get one seed per cell.” They get transplanted into the garden when they have two sets of true leaves and are a minimum of 2 to 3 inches high.
Nancy Knauss, a horticulture educator with Penn State’s Extension, adds that lettuce seedlings should be hardened-off for two to three weeks before moving them into the garden permanently. This process involves gradually increasing the amount of time the seedlings spend outdoors as well as their sun exposure. Providing extra protection to newly planted lettuce transplants during cold nights and days is helpful, as well. Covering the plants with glass or plastic cloches (old milk jugs with the bottoms cut off and the lids removed work like a charm) or with floating row covers increases their chances of success during those fragile first few weeks.
“All this is unnecessary, of course, if you start your lettuce by direct-seeding,” Knauss says.
Fertilize Lettuce Plants
Once your lettuce plants take off, caring for them is a breeze. Kirschenbaum fertilizes his lettuce at planting time with an organic granular fertilizer.
“Lettuce isn’t a heavy feeder at all, so we just use a little bit early in the season but then nothing later in the year,” he says. “But if you have very poor soil, or your plants look weak, you can use a liquid organic fertilizer with a slightly higher nitrogen content.”
Lehmusvirta echoes his thoughts: “I use an organic granular that contains alfalfa meal at planting time, and then during the growing season, I use a liquid fish emulsion or seaweed. After I do my Sunday harvest, I drench the leaves and soil with it and by the time I’m ready for my mid-week harvest, the ‘stinky stuff’ is gone.” Over-fertilizing can result in pest troubles, especially with aphids, so take care not to overdo it.
Water your plants adequately, providing them with at least 1 inch of water per week. They have a very high water content, and lack of moisture promotes early bolting and bitterness. Mulching lettuce plants with compost, leaf mold, straw or hay keeps moisture levels stable and cuts down on unnecessary watering. If possible, irrigate in the morning to discourage fungal issues and pest woes.
Lettuce harvests should take place in the morning, too, because the plants are more turgid at that time.
“The higher the moisture content, the longer the shelf-life,” Knauss says. You can harvest just a few young leaves or uproot the whole plant.
“If you harvest just baby greens, you can get several harvests from each row,” Kirschenbaum says. “Pinch off the older leaves with your fingers, but leave the growing point intact. Or you can use scissors if you want to.”
Lettuce is one of the easiest and most diverse vegetables to grow. It has gourmet-quality flavor and princely good looks with minimal investment of time and money.
“All the success stories involve cool weather,” Kirschenbaum remarks. “Remember that—no matter where you live. And if you don’t have a lot of experience growing different types, then get a seed mix and grow that to find out which varieties you like best. It’s one of those things that even if you don’t have a lot of space, there’s still opportunity—lettuce grows beautifully in containers. You really have no excuse not to grow it!”