ROBERT SIEGEL, HOST:
As the snow melts, even in Minnesota and daylight lingers into the evening, people who like to eat with the seasons know what's coming, asparagus. But global trade is upsetting this vegetable's traditional time table. Almost 90 percent of American's asparagus now comes from abroad. NPR's Dan Charles reports.
DAN CHARLES, BYLINE: Later this month, Nora Pouillon will redo the menu for her restaurant, also called Nora, in Washington D.C. and she'll certainly add asparagus.
NORA POUILLON: Asparagus means the beginning of spring. It's spring. It's spring.
CHARLES: She'll serve those long green spears with salmon, the lower thicker part that people might not like so much, that goes into the soup.
POUILLON: And so I have soup on nearly every day, asparagus soup.
CHARLES: It's an elegant vegetable, Pouillon says, healthy, increasingly popular and different from any other vegetable.
POUILLON: It is sweet and bitter at the same time.
CHARLES: It's not just the taste that sets it apart. Asparagus doesn't grow like other vegetables either. It's a plant that demands patience and long term commitment. Just ask Scott Walker, president of Walker Brothers, the world's biggest asparagus seed company.
SCOTT WALKER: You plant this, this guy right here, and that will be with you for about 10 to 15 years depending on how well you take care of it.
CHARLES: We're in a big barn in southern New Jersey. It's cold in here. Walker is pointing at a pile of dirty tangled roots. These are asparagus crowns, one-year-old plants. Each one grew from a seed in a field in Michigan, a kind of open air asparagus nursery. Now, they're ready to go into production.
WALKER: We ship these all over the U.S.
CHARLES: They travel in refrigerated trucks. Farmers will drop these crowns, which look like big droopy spiders, into long ditches in their fields, cover them up and wait. That root will stay in the ground for a decade or more, growing.
WALKER: It gets to be a very, very large root.
CHARLES: And every year, when the soil warms up...
WALKER: That's when that spear starts to pop.
CHARLES: Farmers don't have a lot of control over the timing. It depends on the weather. But they have to react quickly. When the weather is warm, that root will send up spears that can grow a foot in a single day.
WALKER: I remember one year it went from cold to hot and that looked like the hair on a dog's back out there in that field. It was everywhere and we could not keep up.
CHARLES: Fields have to be picked every day, sometimes twice a day for about six weeks. Walker says there's always been a kind of natural calendar of asparagus production in this country. California is harvesting now.
WALKER: April, we start in Washington state. Late April, Jersey kicks in. Mid-May, Michigan, those guys get going.
CHARLES: But that rhythm is getting badly disrupted by trade and technology. You can get asparagus all winter long now from farms in Peru. Walker's seen those operations.
WALKER: They will harvest in the morning. That night, it's on a plane. The next morning, it's here in the U.S.
CHARLES: But there's also a wave of imports from Mexico right in early spring, prime asparagus season, is making life miserable for asparagus growers in California.
CHERIE WATTE ANGULO: The price is extremely depressed. We haven't seen prices this low in years.
CHARLES: Cherie Watte Angulo is executive director of the California Asparagus Commission.
ANGULO: I refer to this as a marketing train wreck because you have a huge amount of supply on the marketplace right at the time when we're coming on with our new crop.
CHARLES: The basic problem for California's growers is that harvesting asparagus takes lots of hands and labor is a lot more expensive here than in Mexico. So many of California's growers are not even bothering to harvest their crop at the moment. Instead, they're driving through their fields with sharp metal discs that cut off the asparagus spears before they emerge.
ANGULO: This delays production anywhere from a couple of days to a couple of weeks, knowing that in a couple of weeks, a new burst of asparagus will come through the ground.
CHARLES: The farmers are hoping that by that time, the flood of imports from Mexico will be done and prices will be higher again. But some are thinking maybe it's time to stop growing asparagus altogether. That's been the trend. Even though Americans are eating more asparagus, American farmers are growing less of it. Only about a third as much as 20 years ago. Dan Charles, NPR News.