RACHEL MARTIN: Dollar for dollar, California is the biggest agriculture economy in this country. And lately, farmers in that state have been struggling with a new kind of problem. They don't have enough workers to harvest crops. Cardiff Garcia and Stacey Vanek Smith of our Planet Money team went to a celery farm in California to find out more.

CARDIFF GARCIA: We went to Oxnard, Calif., to talk with Tom Deardorff. His family has owned farms in this area for decades.

TOM DEARDORFF: There's probably 80 acres of celery here in the field that we're at right now. Every single stock of celery needs to get cut by hand.

STACEY VANEK SMITH: In the middle of the ocean of celery, there is a crew of about 30 workers? They walk in a row in big straw hats, hacking off celery stalks and tossing them onto this motorized platform which stretches across the field and chugs along behind them.

It is really hard and dangerous work, 10-hour days swinging a knife in the hot sun. And when the job market's strong, like it has been for the last few years, these workers have a lot of other options.

DEARDORFF: They move into - whether it's landscaping jobs, construction jobs, food service jobs.

GARCIA: So Tom Deardorff has had to compete for workers. He's raised their pay by actually quite a lot. Back in 2006, working the celery field paid about $8.70 an hour. Now it pays more than $21 an hour. We couldn't speak to any of the workers on Tom's farm. But Tom says his workers all are documented and that even doubling wages hasn't solved the labor problem.

DEARDORFF: Yeah I don't think it's an economic issue. I think it's a political issue.

GARCIA: Tom says the agriculture visas that the country offers - they're too difficult to get, they're expensive and there just aren't enough of them. Deardorff Farms used to hire more than 600 workers every year. But Tom says he can't make that happen anymore, so he's had to make changes to his business.

DEARDORFF: We've shifted away from the most labor-intensive crops - so things like vine-ripe tomatoes, we no longer grow anymore. We've also shifted a large amount of our production down into Mexico. So basically, the fact of the matter is that a foreign-born person is going to be harvesting your fruits and vegetables. So the decision is - do we want to do that within the United States, or do we want to have that foreign-born worker stay in his country and harvest your fruits and vegetables? So based on what we've seen in the political environment over the last 15 and 20 years, we have decided to go down there into Mexico.

GARCIA: And now with President Trump signaling that he wants to crack down on undocumented workers, the labor situation might get even harder.

VANEK SMITH: Even if Tom only hires documented workers, he could feel the pinch because if undocumented workers leave the area, the overall supply of farm workers goes down. So more and more farmers could find themselves moving their operations to Mexico.

GARCIA: How hard was it to make these kinds of decisions based on, like, what you were seeing?

DEARDORFF: I mean, if I was looking at spreadsheets all day long, it was a really simple decision and one we probably should have made five years before we made it. But I mean, these are ranches that my great-grandfather farmed, and we'd rather keep them active. But the economics and the politics of it are suggesting that we do otherwise. So...

VANEK SMITH: Tom says his business has become this constant calculation of how to harvest more with less because, in spite of everything - the higher pay, the different crops - his turnover rate keeps growing. Fewer and fewer of the same workers come back to his farms every year.