Lettuce (Lactuca sativa), endive and escarole (both Cichorium endivia) are members of the Asteraceae plant family, and all originated in the Mediterranean region. Their closest crop relatives are artichoke, chicory and sunflower.
Lettuce grows best at cool temperatures, making spring and fall the major production seasons in New England. While endive and escarole are also cool-season crops, they are more tolerant of high temperatures than lettuce and therefore make a good substitute for lettuce during the warmer mid-summer weather.
Types and Varieties
There are five common types of lettuce. Crisphead or iceberg is commonly found in produce markets. The leaves are thin and crisp, often with curled or serrated edges, and the head should be firm. Butterhead or bibb lettuce has a loose-leafed head with green or red outer leaves and cream or yellow inner leaves. Butterhead type lettuce requires careful handling as it bruises and tears easily. For this reason, it is best suited to local market sales. Cos or romaine is an upright plant with the smooth outer leaves and whitish green inner leaves. Some think the leaves are crisper than other heading types. The fourth general type is variously named leaf lettuce, loose leaf or loose head. Lettuce of this type does not form a head and the leaves may be serrated, deeply lobed or crinkled. Leaf lettuce color varies from light green to red to green with red speckles, adding attractive color to salad mixes. The fifth type is “one-cut” lettuce. Several different proprietary lines of one-cut lettuces are sold through various seed distributors. This lettuce type has a high leaf count and narrow leaf attachment, so can be harvested easily as a whole head (by cutting at the base) or loose-leaf (by cutting just above the base). Unlike most leaf lettuces, one cut lettuces are usually transplanted, which allows for quicker bed turnover. One-cut lettuces can have variable leaf shapes (smooth, lobed, serrated), colors (green, red) and textures (tender/butter-like, crisp/romaine-like).
Endive and escarole encompass many diverse types. Escarole and Frisée are types of endive (Cichorium endivia), both of which form loose and leafy heads. Radicchio and Belgian endive are forms of chicory (Cichorium intybus) that form small, tight heads. Belgian endive is grown in two stages: during spring/summer, the seeds produce large dandelion-like leaves and a large taproot, similar to carrot. In the fall, the taproots are dug, and potted and placed in the dark. The new growth from the roots produces small tight heads called chicons, which are marketed. Italian (or "culinary") dandelions form long leaves that are usually bunched.
|Lettuce, Endive and Escarole Varieties|
|Lettuce - Butterhead||Lettuce - Crisphead|
|Adriana - DM, LMV||Caretaker - TB|
|Buttercrunch - DM, LMV||Crispino|
|Milagro - DM, LMV|
|Skyphos (red)||Lettuce - Leaf|
|Lettuce - Romaine||New Red Fire (red)|
|Coastal Star||Starfighter - DM, HT|
|Sparx - DM||Two Star|
|Winter Density||Muir - DM, LMV|
|Rouge d'Hiver (red)|
|Resistant or tolerant to: DM: Downy Mildew; LMV: Lettuce Mosaic Virus; TB:Tipburn|
In general, lettuce, endive and escarole have the same fertility, spacing and seeding requirements. Apply lime according to soil test results to maintain soil pH at 6.5-6.8 and maintain soil calcium levels. Low soil calcium levels may increase the incidence of tip burn. Tipburn is a disorder that causes the margins of leaves to turn black and decay. It is of particular concern with iceberg and romaine types where tipburn on internal leaves may not be immediately obvious. Over-application of nitrogen on fertile soil can result in very rapid growth which can trigger tipburn. Banding the preplant fertilizer at planting is preferable, but if not possible, then broadcast and incorporate the initial application. Less nitrogen fertilizer will be needed if legume sod was plowed down or if manure was applied (see Table 1 and Table 7).
|PLANT NUTRIENT RECOMMENDATION ACCORDING TO SOIL TEST RESULTS FOR LETTUCE, ENDIVE, AND ESCAROLE|
|LETTUCE, ENDIVE, AND ESCAROLE||NITROGEN (N) LBS PER ACRE||PHOSPHORUS (P) LBS P2O5 PER ACRE||POTASSIUM (K) LBS K2O PER ACRE|
|SOIL TEST RESULTS||VERY LOW||LOW||OPTIMUM||ABOVE OPTIMUM||VERY LOW||LOW||OPTIMUM||ABOVE OPTIMUM|
|Broadcast and Incorporate||50-75||180||120||30-60||0-30||180||120||30-60||0|
|Sidedress 3-4 Weeks after Planting||30-50||0||0||0||0||0||0||0||0|
Generally lettuce, endive, and escarole have the same spacing and seeding requirements. Final spacing on crisphead lettuce, endive, and escarole should be 12-18" between plants (67-100 plants per 100 feet of row) and 12-24" between rows. Other types of lettuce can be 10-16" apart (75-120 plants per 100 feet of row) in 10-18" rows. Spacings should allow good air movement around the plants to minimize disease development. Many growers raise lettuce, endive, and escarole on 4' wide, raised, 4" high beds with 3 to 4 rows per bed. Crop rotation within and between seasons is recommended for disease management. For direct seeding, 10 to 18 oz of seed are needed per acre (0.0625-0.125 oz per 100 feet of row).
Lettuce will germinate at soil temperatures of 32ºF, but the optimum and maximum soil temperature is 75ºF. Temperatures above 80ºF will inhibit seed germination and cause bolting in lettuce. Temperatures below 70ºF will promote bolting in endive and escarole. Lettuce seed requires light to germinate and so should be seeded to a shallow depth.
For once-over harvesting, uniformity at harvest is essential. Producers for direct retail markets and CSA might prefer variable maturity. Precision seeding with modern planters and coated seed can enhance uniformity. Irrigation immediately after seeding also promotes uniform emergence.
Since lettuce matures quickly (40-50 days), and temperature affects days to harvest, plant several successions to get consistent production into the summer.
Lettuce is often started from transplants, which can be planted all season, from mid-April to August 1. Some growers use floating row covers over beds with early transplants for earlier crops. Hardened transplants should be set out when they are 3-4 weeks old. Hardening is accomplished by withholding water and gradually reducing temperatures for 10 days before the planned transplant date. Use of a liquid starter fertilizer at transplanting time can reduce shock and provide immediately available nitrogen and phosphorus in cold soil. Use a dilute solution to avoid injury to roots. In hot summer conditions, starting transplants in the greenhouse or shade house provides better germination than in the field.
Hot temperatures cause lettuces to develop a bitter flavor and promote bolting. White on black plastic mulch (white above, black below) can be used to cool soil temperatures and reduce development of bitterness and bolting. Shade cloth can also be used to reduce heat stress in lettuce. Choose heat-tolerant varieties for mid-season production.
Harvest and Storage
Head lettuces should be harvested when heads are well-formed and solid by cutting at the base. A few wrapper leaves should be left on each head to protect during packing. Leaf lettuces can be harvested by hand or mechanically; a single crop can be harvested multiple times.
Food safety issues from microbial contamination are often linked to leafy greens that are eaten raw. It is important to follow some basic practices that are in accord with the guidance outlined in the Food Safety section of this guide.
Lettuce, escarole, and endive are fragile and highly perishible. Heading lettuces, endive, and escarole are more easily stored than leaf lettuces. Cool to 32-34ºF as quickly as possible after harvest and store at 98-100% relative humidity. These crops are damaged by freezing temperatures (32ºF).