Bronze Arrow Lettuce in Frost
- Lactuca sativa L.
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.
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
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:
||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
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
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
till next month,
Good Gardening and Good Eating
Doña Ana Extension Master Gardener