Romaine lettuce is known by many names, including Cos lettuce, Roman lettuce and Manchester lettuce. Although romaine is the most common name in North America, this variety will occasionally be referred to as Cos lettuce. Cos refers to a Greek island located off the southwestern coast of Turkey, where this lettuce variety is said to have originated. Originally used as a cooked vegetable, romaine lettuce is one of the oldest cultivated vegetables.
TYPES, VARIETIES & CUTS
Romaine is an elongated, heading type of lettuce with pronounced, firm ribs. A cool season crop, types and varieties will vary in color (green or red) and how tightly the leaves close, often referred to as “self-closing” or “loose closing” depending on whether the leaves curl inward at the top to form a head. Romaine hearts are the tender, yellow interior leaves known for their mild, sweeter flavor.
PESTS & DISEASE
Tip burn can be caused by several factors, including variety, soil conditions, and temperature fluctuations. Leaf margins can become damaged and susceptible to decay. Pink rib is prevalent with over-maturity and warm temperatures in storage. Ribs will take on a pink hue. Brown stain, as its name suggests, presents with yellow- or reddish-brown spots and stains on ribs and may expand and darken in time.
Soft rot is caused by bacteria and results in a translucent, slimy breakdown of infected tissue. Trimming outer leaves, rapid cooling, and low temperatures can reduce development and spread. Other disorders and diseases of concern include big vein, Botrytis grey mold, bottom rot, downy mildew, leaf drop, mosaic virus, and powdery mildew.
Pests to watch out for include aphids, armyworms, beetles, crickets, cabbage loopers, cutworms, leafminers, leafhoppers, thrips, whiteflies, and wireworms.
CULTIVATION, STORAGE & PACKAGING
Romaine requires nutrient-rich, well-drained soil and can be direct seeded or transplanted. Due to shallow roots, drip irrigation is the best way to maintain moisture. Mulch can help reduce weeds and regulate soil temperature.
Harvest is labor intensive and lettuce is either packed ‘naked’ or wrapped or bagged. Rib breakage can occur during harvest and packing, especially with over-mature heads, resulting in browning and higher susceptibility to decay. Product harvested early in the morning, when temperatures are lowest, is more vulnerable to rib damage.
A steady temperature of 32°F with 95% relative humidity will optimize shelf life for up to 3 weeks. Romaine can tolerate slightly higher temperatures during transit and handling, lacking other complications (such as ethylene gas). Romaine is sensitive to ethylene and damage can appear as discolored spots on the rib. These are generally larger and less defined than russet spotting on iceberg lettuce. Variety can dictate susceptibility. Common containers are bushels or cartons holding about two dozen heads.
There is only one grade for romaine lettuce, U.S. No. 1, and there are no grade standards for Canada. For U.S. No. 1 romaine, plants should be of similar varietal characteristics, fresh, well-developed, well-trimmed, and free from decay and damage including broken, bruised, or discolored leaves or ribs, tip burn or wilting, freezing injury, dirt, incidence of disease, or insects.
References: University of Arizona Cooperative Extension, University California Vegetable Research & Information Center, University of Kentucky Cooperative Extension, USDA.