Lettuce, endive and escarole are members of the Asteraceae plant family, and all three crops originated in the Mediterranean region. Their closest crop relatives are artichoke, chicory and sunflower. Endive and escarole are the same species, Cichorium endivia, whereas lettuce belongs to the species Lactuca sativa.
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 and frequently have curled or serrated edges. Today's consumer is looking for a firm, durable head. Butterhead or bibb lettuce is a head type with loosely folded leaves. The outer leaves are green or red while the inner leaves are cream or yellow. 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 outer leaves smooth and green and the inner leaves whitish green. Some think the leaves are more crisp than other heading types. Leaf lettuce, loose leaf or loose head are all names applied to the fourth general type. 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, adding attractive color to the salad or dinner plate.
Escarole has broad leaves that are arranged in a loose head. Endive, also knows as frisée, has slender curly leaves, also arranged in a loose head.
|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 to 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. If the fertilizer cannot be banded at planting, add the band fertilizer amount to the preplant broadcast application. Less nitrogen fertilizer will be needed if manure or legume sod was plowed down (see section on nitrogen credits).
|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|
|*SEE PLANT NUTRIENTS FOR INFORMATION ON NUTRIENT MANAGEMENT AND APPLICATION.|
Final spacing on crisphead lettuce, endive, and escarole should be 12" to 18" between plants (67 to 100 plants per 100 feet of row) and 12" to 24" between rows. Other types of lettuce can be 10" to 16" apart (75 to 120 plants per 100 feet of row) in 10" to 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 three to four 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 to 18 oz of seed are needed per acrre (0.0625 to 0.125 oz per 100 feet of row).
Lettuce will germinate at soil temperatures of 32°F, but the optimum and maximum soil temperature is 75°F. When seeded at a soil temperature of 80°F, the seed will not germinate but rather remain dormant until cooler temperatures prevail. 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. Because lettuce is generally harvested on a once-over basis, uniformity at harvest is essential. Growers should purchase the best quality seed available to help ensure the uniformity of the crop. Precision seeding, with modern planters, and coated seed can enhance uniformity. Irrigation immediately after seeding also promotes uniform emergence.
Since lettuce matures so quickly (40 to 50 days), and days to harvest is impacted by temperature, it is crucial to plant several plantings of lettuces to get consistent production throughout the summer.
Transplants are often used for lettuce production. Transplants can be used all season, from mid-April to August 1. Some growers find that the use of floating row covers over the bed in combination with early transplanting will provide an earlier lettuce crop for a specialty market. Hardened transplants should be transplanted when they are 3 to 4 weeks old. Hardening of lettuce transplants is accomplished by withholding water and gradually reducing temperatures for 10 days before the planned transplant date. If using transplants, use of a liquid starter fertilizer at planting time can reduce transplant shock. If using a starter fertilizer, mix at a rate of 2 lbs/50 gal water and apply 4 to 8 fluid ounces per transplant. Harvest will be in about 6 weeks. 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 on one surface and black on the other (white on black) for growing lettuce and other cool season vegetables. White-on-black plastic cools soil temperatures by up to a few degrees in high temperature conditions; this small amount of cooling can reduce the tendency of lettuces to bolt in high temperatures.
Harvest and Storage
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 (32F), but should be cooled as quickly as possible and maintained as close to 32F as possible with 98-100% relative humidity.