Hawai‘i Island Barefoot Gardener: Simply Lettuce
January 5, 2018, 11:45 AM HST
* Updated September 8, 10:58 AM
Many people love lettuce in a salad, though I have heard some people proclaim that it doesn’t have enough nutrients to stain your shirt. One thing is for sure though—love it or leave it, lettuce is will always be a standard in most gardens.
There are numerous types of lettuce. From hearty butter lettuce to delicate Romaine, these leafy greens come in enough cultivars to suit almost all tastes and climates. Lettuce can be visually appealing as well.
Lettuce has one of the longest domestication histories of any garden vegetable. Believed to have originated from wild lettuce (Lactuca serriola L.) in the Mediterranean basin, the earliest known accounts of lettuce are found in Egyptian tomb paintings dating back over 4,500 years ago. The first written accounts of lettuce describe its appearance on the royal tables of Persia in 550 B.C.; Hippocrates ascribed medicinal properties to lettuce in 430 BC and Aristotle mentions this prolific member of the sunflower family in 356 BC. Lettuce proved to be popular in ancient Rome, and it is believed that the Romans introduced it to Europe.
Christopher Columbus is credited with having introduced many vegetables to the New World, lettuce among them. The first commercial lettuce fields sprang up in New York. During the early part of the 20th century, brown blight decimated the New York lettuce fields, prompting the USDA to employ the expertise of plant breeder I.C. Jagger to develop blight resistant cultivars. The result was the “Imperial” cultivar. A later variation of Imperial also proved to be resistant to downy mildew.
It wasn’t until the 1940s that “Iceberg” lettuce appeared. Known for its firm, crispy leaves, mild flavor and high water content, Iceberg was wildly popular well into the 1970s. In 1975, the USDA released a crisp head lettuce cultivar called “Salinas,” which remains the most widely grown lettuce in the United States.
Regardless of which cultivar you choose, lettuce is a fast-growing and rewarding crop. If you wish to sell your produce at the local market or just have it for your table, you will find it quite easy to grow an abundant supply. The key to always having ready-to-pick lettuce in your garden is to start new seeds every two to three weeks.
Lettuce enjoys a well-tilled loam, high nitrogen, and a slightly acidic pH (6.0–7.0). When choosing lettuce seeds or starts, be sure to choose a heat-resistant variety if you live in West Hawai‘i or in the lower elevations. Cultivars that are not heat resistant tend to “bolt” early, meaning that leaves become tough and bitter while the plant sends up a central shoot that produces flowers and seeds. I have found that most Romaine varieties do quite well in a tropical climate. For cooler climes such as Volcano and Waimea, Black-Seeded Simpson is always a winner.
If starting from seed, sow them 1/8 inch in depth and approximately 9 to 12 inches apart. Like most garden vegetables, lettuce requires full sun; however, it will do well in an area that receives partial shade for the latter portion of the day.
Keeping lettuce cool in hot weather is important; using a mulch of bark and shredded leaves works quite well.
One concern on the Big Island regarding soil-grown lettuce is the presence of slugs, which carry rat-lungworm disease. There are several effective ways to deter slugs and snails from lettuce.
I have been successful using shredded bamboo leaves around lettuce, as insects, slugs and snails don’t like crawling over the stuff and bamboo’s high silica content keeps moisture in the soil and retards weed growth. If you decide to use bamboo leaves, do not allow it to touch the lettuce, lest it retard the growth of your crop.
Seaweed mulch is also an excellent deterrent, and is well worth the time to go out and gather.
Other effective slug and snail deterrents include crushed eggshells, diatomaceous earth (DE), citrus rinds, sandpaper and copper tubing.
Fertilize your crop with fish emulsion or an organic seaweed fertilizer every two weeks and you’ll have plenty of fresh lettuce in 45 to 65 days.