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frosted Lettuce
Bronze Arrow Lettuce in Frost

Lettuce - Lactuca sativa L.
Compositae Family

Lettuce is considered by most to be a cool season crop best planted in early spring and again in late summer or fall in more southern climates. That is a good practice, but if you enjoy green summer salads, you can now grow lettuce year round by changing varieties and culture methods.

Heritage

Cultivated lettuce originates from the wild ancestor Lactuca scariola, today found widely scattered around the world. Its original home is the trans-Caucasus Mountains of Iran and Turkistan. Its not as old as many other cultivated edibles, but Greek and Persian writers wrote about lettuce in the 6th, 5th and 4th centuries BC and Roman writers described a dozen distinct varieties with many of them quite common.

Lettuce also shows up in Chinese writings in the 5th Century BC. There’s even a description of a wild “stem lettuce” harvested for its tall fleshy edible stem. “Stem lettuce” seed is available today in specialty catalogues and can be grown in the home garden. However, if you want something similar, let your lettuce plants bolt and eat the bloom stalk (delicious when baked!).

Lettuce was a well-established crop throughout Europe by the time of Columbus’s second voyage (1493) and settlement (Isabella) on the north coast of modern-day Dominican Republic. He introduced lettuce there, but it did not grow well in the hot moist climate. The first record of lettuce in New Mexico dates to the Juan de Oñate’s settlement expedition in 1598.

Varieties and Seasons

Varieties matter when growing lettuce on a year-round schedule. During the cooler seasons when daytime temperature remain below 90F nearly all lettuce varieties will grow well and remain sweet until they bolt. However, during late spring and summer when daytime temperatures exceed 90F only those varieties that are bred to be heat tolerant will deliver edible lettuce. I have grown the following heat tolerant varieties and I am satisfied with their growth and taste:

Heat Tolerant Varieties Nevada - Batavia
Red Sails - Loose Leaf
Matchless - Bibb
Red Butterworth - Looseleaf
Jericho - Romaine
Buttercrunch - Bativia
Sweetred - Butterhead
Torenia - Butterhead

Growing in summer

During summer you will need to start seed under lights and set out transplants when about 3 weeks old – do not delay transplanting beyond 4 weeks for best results.
Space transplants on a 12-inch grid, allowing more root space than for cool season plantings. These plants require more water to cool off through transpiration. Based on water use experiments I did last July and August each plant needs about a gallon of water daily when full grown. Since even heat tolerant lettuce varieties can become bitter with water and/or nutrient stress – grow them in rich soil with plenty of root space.

Ideal timing for summer lettuce is 20 days from seed to transplant and 20 – 30 days from transplant to full head development. There can be 10-20 days difference in growing time depending on variety as some summer varieties are quick to bolt and some are slower. For more information about growing lettuce during the hot season – refer to the article Summer Lettuce.

Growing in cool seasons

You can grow both “cut and come” and heading lettuces during the cool season. For “cut and come” sow seeds closely and shallowly, then harvest individual leaves at about 3 weeks and two successive times after that. Eventually those plants will begin to grow leaves that are tough and make poor salads.

You can sow seeds in “stations” on an 8-inch grid and harvest the outer leaves as the plants grow, and/or let the plants come to maturity before harvest. During the cool seasons, you can also start lettuce under lights and set out transplants – but it is not necessary to do, as the seed will germinate easily with soil temperatures below 80F. Remember to sow seeds very shallowly, barely covered, as lettuce seed needs light to germinate.


Biology and Nutrition

To grow quickly and well until mature, lettuce roots need soil that has plenty of available nitrogen, phosphorous, potassium and calcium. Our soils are generally high in potassium, but may not contain adequate available calcium for maturing lettuce. The last two weeks prior to full growth and while holding in cooler weather your lettuce may develop tip burn or browning on the outer edges of the older leaves. Uneven watering and calcium deficiency can be the cause. During this time, lettuce stops growing new rootlets, which are the most efficient at calcium uptake. Adding bone meal before planting will usually prevent the problem.

With minimal space and effort and a little knowledge you can “grow your own” lettuce year-round. Your garden space can be pots on the balcony or any space that receives at least six hours of direct sunlight daily throughout the year.


till next month,
Good Gardening and Good Eating

Darrol Shillingburg
Doña Ana Extension Master Gardener

December 2010

 

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