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 four 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 green inner leaves whitish green. 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 the salad or dinner plate.
Endive and chicory encompass many diverse types. Radicchio forms small, tight heads. Escarole and Frisée are types of endive, both of which form loose and leafy 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|
|Butterhead Lettuce||Crisphead Lettuce|
|Adriana - LMV, DM||Keeper|
|Buttercrunch - LMV, DM||Summertime|
|Romaine Lettuce||New Red Fire|
|Medallion - LMV||Red Sails|
|Green Forest||Slobolt - TB|
|Green Towers||Tehama - TB|
|Winter Density||Two Star|
|Rosalita||Vulcan - TB|
|Valley Heart||Green Vision|
|Salad King||Full Heart|
Resistant or tolerant to: DM: Downy Mildew; LMV: Lettuce Mosaic Virus; TB:Tipburn
Generally 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 affect 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 or 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, page 2 and Table 7, page 15).
|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|
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 grey mold (Botrytis), bottom rot (Rhizoctonia), and drop (Sclerotinia). Many growers raise lettuce, endive and escarole on 4' wide, raised, 4" high beds with 3-4 rows per bed. This enhances air movement and drier soil conditions for disease control. Growers are also urged to rotate lettuce wherever possible to reduce problems with drop and corky root rot, which can be common when double cropping in the same field. For direct seeding, 10-18 oz of seed are needed per acre (0.0625-0.125 oz per 100 feet of row).
Lettuce will germinate at soil temperatures of 32º F, but the optimum and maximum soil temperature is 75º F. When seeded at a soil temperature of 80º F, the seed will not germinate but rather remain dormant until the temperature lowers. Lettuce that is already established and subjected to high temperatures will bolt and form a seed head. Generally lettuce, endive and escarole have the same spacing, seeding and fertility requirements. 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.
Transplants are often used for lettuce production and can be used 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- to 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. Varieties that do well as transplants even in mid-summer and are very slow to bolt include Adriana (Boston), Slobolt (green leaf), New Red Fire (red leaf), and Green Forest (Romaine). In hot summer conditions, starting transplants in the greenhouse or shade house provides better germination than in the field.
Many growers that use polyethylene mulches for water conservation and weed control prefer to use plastic that is white above and black below (white on black) for growing lettuce and other cool season vegetables. It can cool soil temperature by up to a few degrees in high temperature conditions and can reduce the tendency of lettuces to bolt.
Harvest and Storage
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. In general, lettuce, escarole and endive are fragile. Heading lettuces, endive and escarole are more easily stored than leaf lettuces. Low temperatures and high relative humidity are needed to prevent wilting. These crops are damaged by freezing temperatures (32º F), but should be cooled as quickly as possible and maintained as close to 32º F as possible with 98%-100% relative humidity.