The effects of the four-year drought continues to rock California’s bread-and-butter – the agricultural industry.  

Due to water troubles, the drought could force some late summer lettuce production to shift from the Huron area in Fresno County to the south in the winter desert vegetable production areas in southernmost Imperial County and neighboring Yuma County, Ariz.

“Drought conditions in the West are affecting many different cropping systems,” said Kurt Nolte, director of the University of Arizona (UA) Cooperative Extension in Yuma County.

“We’ve been asked to investigate the possibility of growing lettuce in Yuma to fill the Huron slot due to drought.”

Nolte discussed this potential change during the 2015 Fall Desert Crops Workshop in Imperial, Calif. The event was sponsored by Western Farm Press along with commercial suppliers.

“If the Huron area were removed from the (California-Arizona) lettuce-growing program then the desert would have to pick up the slack,” Nolte told the crowd of desert growers, crop consultants, pest control advisers, and others.

Shift growing season up a month

If late-summer production moved to the desert, it would require lettuce plantings start a month earlier in mid-August, ahead of the traditional winter lettuce plantings which start in mid-September. Lettuce planted in mid-August would be harvested in mid-October, a month earlier than the traditional harvest start in mid-November.

There are so many questions on whether this could work. Could seeds tolerate the 110 F.-degree desert heat in August? Could a crop shift be economically viable for desert growers? What crop management changes might be required? Could a truly wet El Nino winter help ease water concerns in the Huron area and delay or eliminate the need to switch of the desert?

University of Arizona trials

In a search for potential answers, the University of Arizona (UA) has completed the first year of a three-year study on this feasibility with lettuce, mostly iceberg head lettuce, in the desert.

The study is sponsored by the Arizona Iceberg Research Council, largely through specialty crop grant funding through the Arizona Department of Agriculture.

Currently, growers in California’s Salinas Valley grow about 85-90 percent of the nation’s summer supply of vegetables, while Yuma and Imperial county growers produce about the same amount during the winter months. Huron growers help fill in the production slot as production shifts between the two top vegetable areas. 

Trials conducted this year focused on several growing options including direct seeding into fields a month earlier than usual.

Premature bolting?

Nolte said, “The challenges we face planting lettuce by direct seeding in July and August resulted in premature plant bolting – triggered by longer day length - where pre-mature flower stalks formed in iceberg, romaine, and leaf lettuce plants.

Nolte compared the problem to a car or truck.

“Turn on the engine for a long day and this triggers the plant to flower. Putting your foot on the gas pedal triggers the rapid growth of the flower stalk in lettuce.”

Besides direct seeding, lettuce transplants were grown from seed for field planting at Greenheart Farms in Yuma, plus at the main UA campus in the Controlled Environment Environmental Ag Center.

Transplants were also grown in much cooler locations, including on the California Central Coast, and Arizona locations in Flagstaff and Prescott locations.

Seed vs. transplant comparison

Nolte shared a busy PowerPoint slide, comparing the crop results from field tests: the traditional direct seed method in mid-September in Yuma, moving up the direct seed date to mid-August, transplants grown in the summer in Yuma and Tucson and then planted in fields in mid-August, and transplants grown in much cooler environments.

Here is a breakdown of the findings from each method.

Traditional method - direct seed in mid-September– Desert fields are typically direct seeded in Yuma in mid-September – sprinkler water germinates the crop - harvest begins in mid-November - head weight averages 1.25 to 1.5 pounds with good internal density - core length is 1.5-2 inches – with no plant bolting.

Direct seed in mid-August – Grown the same way as above but a month early - harvest in mid to late October – lettuce quality was poor with half the head weight - internal density was more puffy – plants grew too fast – the core was double the normal length.

Summer transplants grown by Greenheart Nursery and the UA in Yuma, planted in mid-August – results were similar to direct seeding in mid-August – it was too hot for the transplants – plants bolted, had long cores and puffy internal density – “Essentially not a very marketable crop,” said Nolte.

Cooler-grown transplants - growth chamber-grown seedlings in trays in greenhouses in cooler locations - drastically improved plant results – transplanted in mid-September and harvested in mid-October - head weight slightly less than normal – internal density about the same – core length was slightly larger – and no bolting.

Based on these results, Nolte says cooler-grown transplants have the definite edge to produce a good lettuce crop.

“These cooler-grown transplants showed that a good lettuce crop can be grown and harvested a month earlier in the desert.”

Many questions to explore

A huge question would be the costs of cooler-grown transplants. Nolte says transplants would costs more than direct seeding. However, transplants would eliminate plant thinning associated with growing from seed which would reduce growers’ labor costs. With transplants, there would be a shorter growing time in the field which could reduce bird damage.

In addition, less water could be required using transplants compared to irrigating an entire field from the seed-seedling stage.

Yet many questions remain.

Nolte said, “We are unsure about the survival rates of transplanted lettuce in August. We also do not know yet about possible crop management changes.”

Research over the next two years will focus on whether the crop could be grown even earlier with planting transplants as early as late July. 

The 26^th annual Fall Desert Crops Workshop was organized by the University of California Cooperative Extension Service in Imperial County.

Commercial workshop sponsors included: Platinum Level – Adama, BASF, and Bayer CropScience; Gold Level – Dow AgroSciences, Gowan USA, and Westbridge Agricultural Products; and Silver Level – ORO AGRI.