Late Fall to Spring Leaf Lettuce Trial
Results from four separate trial runs of nine leaf
cultivars
in NFT production systems
Dr. Natalie Bumgarner
Objectives
Hydroponic lettuce production in the United States
now encompasses a wide spectrum of lettuce types and cultivars. While Bibb
cultivars still occupy a large percentage of the market, many growers are also
seeking attractive and distinctive lettuce cultivars to meet consumer demand.
Due to these factors, leafy cultivars, including looseleaf and Lollo types, are
becoming more common in hydroponic greenhouses. However, some of these
cultivars have been more often grown in soil based systems, and there is a need
to better understand their performance in the greenhouse. Consistency in both
productivity and timing is important for greenhouse growers, and seasonal
conditions can have a large impact on cultivar performance. Trialing of
available cultivars under differing conditions is important in informing grower
decisions. Important points of evaluation are growth rate, yield and visual
coloration. The goal of this set of trials was to evaluate a selection of leaf
lettuce cultivars through a range of late fall, winter, and early spring
conditions to evaluate their potential for greenhouse growers in the Midwest
and northeast. Cultivars were obtained from varied seed suppliers to represent
a broad selection of cultivars available to lettuce producers.
Methods and Management
Primed and pelleted seeds were seeded by hand in
pre-moistened 1” x 1” x 1 ½” rockwool cubes. Seeds were germinated in clear
water in seeding trays in the nursery. Nutrient solution was added in the
nursery 7 days after seeding and lighting was used for the seedling phase (T5
florescent fixture) and seedlings were grown in flowing nutrient solution in
the nursery for approximately two weeks before transplanting. After
transplanting, lettuce plants were grown out in the channel for five weeks
prior to harvest. The nutrient solution was continually cycled through the
CropKing Fertroller where automatic pH and EC adjustments met programmed
solution set points. The pH was maintained at 5.8 by the addition of dilute
sulfuric acid. EC was maintained at 1.8 by the addition of concentrated
fertilizer solution and source water.
* It is important to note that these trials were
carried out over set periods of time and harvests were made regardless of plant
readiness for sale. Clear comparisons were the main goal, and this resulted in
low weights for some cultivars. Also, no supplemental lighting was used after
transplanting even under these low light northern conditions. In a commercial
operation, more time would have been give these heads to reach a saleable size
or lighting would have been added to increase growth rate and crop
quality.
Some Concluding Thoughts
There are always many interesting observations from
cultivar trials carried out across different seasons. From these trials, I would like to make a
couple observations in addition to the common trends of 1) decreased growth
under lower light/winter conditions, and 2) more dense, compact, and more
deeply pigmented lettuce grown under higher light levels.
The first important take-away from these cultivar
trials is the importance of understanding your customers and market demands
when selecting a lettuce cultivar. While it is a generally true statement that
different lettuce cultivars grow at different rates, these differences can be
clearly seen in this selection of leaf lettuces. For example, the Tropicana cultivar
is a typical green leaf crop sold for soil production that can also be grown in
the greenhouse. As can be seen in the images and yield numbers, this green leaf
lettuce has a more rapid growth rate than the Lollo Biondo (blond, such as
Livigna and Lozano) or Lollo Rossa (red, such as Carmesi and Orville)
