Last summer, plenty of drama emanated from California’s Salinas Valley, epicenter of industrial vegetable production (organic and otherwise) and self-proclaimed “nation’s salad bowl.”

The season began amid grumbles among growers about a labor shortage. To paraphrase their complaint: Not enough Mexican workers are sneaking across the border, and ones who are are drawn into higher-paying construction jobs.

The season ended in an ignominious nationwide E. coli outbreak that killed three people and sickened hundreds of others.

About this time each year, industrial vegetable production shifts to Arizona’s Yuma County, source of 90 percent of winter vegetables in the U.S. and (gasp) 98 percent of its iceberg lettuce. Let the drama begin.

Yuma county growers are complaining bitterly of, you guessed it, a labor shortage. Yuma lies along the Mexican border, now teeming with cops and nativist zealots. If you were an undocumented worker, wouldn’t you stay away?

In a theoretical market situation, the growers would simply jack up their wages, draw in more workers, and pass the price on to the big supermarket chains, which would in turn pass the increase on to consumers.

In the real world, though, two factors prevent that scenario. First, few U.S. citizens are willing to spend their time in a field harvesting lettuce at any wage, and undocumented workers are staying the hell away from the border to avoid the cops.

Second, big buyers like Wal-Mart — erstwhile savior of organic agriculture — hold the trump card in this market. If Arizona growers jack their prices up, the Wal-Marts of the world will just buy from Mexico or elsewhere. The border may impede the flow of labor, but goods flow freely.

So when there’s a labor shortage in Yuma, growers typically find it makes the most sense to let crops rot on the vine. Brilliant system, huh?

Meanwhile, there’s another situation that should generate drama but doesn’t: Yuma County growers rely on the Colorado River for irrigation, and the river is polluted with perchlorate, the rocket fuel used by the Pentagon to fuel the U.S. war machine.

The Environmental Working Group has found significant traces of the vile stuff on lettuce; the Bush Administration says it’s no big deal.

I say, work with local farmers to invest in season-extension infrastructure, so you can get your winter vegetables under less, um, dramatic circumstances.

While you’re working on that, plant a winter garden under a cold frame.