In June, the calls to Dennis Jensen’s Riverside County date farm in Southern California began to pick up. By July, he said, the calls took on a more urgent nature: “Send me some dates; save me!”

Wholesalers and grocers were rushing to put their orders in for Ramadan, the Muslim holy month that begins today. During Ramadan, Muslims fast from sunrise to sunset, followed by evening meals that commence with at least one date, a practice believed followed by the prophet Muhammad.

Preferences for the fleshy fruit run from the drier “deglet noor” to the sweet Medina to the hard, yellow “barhi.” But the most sought-after dates — especially among Middle Easterners — are the soft, plump “medjool.”

Nearly all “medjools” in the United States come from the Coachella or Imperial valleys in California. Growers here also sell dates to Europe, Malaysia, Indonesia, Australia and even some Middle East countries, where the local “medjools” are eclipsed by California’s.

But this year, the calendar has thrown a wrinkle into the date business. It will be the first time in a decade that Ramadan starts before the harvest season in September. The holy month follows the lunar calendar and moves forward each year about 10 days.

This means that most dates will come from last year’s crop, stored in freezers. Some fear a date shortage, or at least a scarcity of the most popular varieties.

“All the date-growers have known that Ramadan runs on a lunar calendar, so we’ve been watching this for several years,” Jensen said. “Mother Nature has other games and doesn’t care when Ramadan is.”

Last year, the Coachella Valley produced 20,687 tons of dates with a market value of $32.1 million, according to the annual crop report. Jensen’s farm produced about 480,000 pounds of dates, with roughly 70 percent going to fill orders for the Muslim observance.

By now, most of Jensen’s 2008 crop has been sold, but the calls keep coming. For the last several weeks, all that have remained are the jumbo “medjools,” the most expensive grade of the most expensive date. But as Ramadan nears, even this costly variety may become unavailable.

On a hot and humid July morning, Jensen turned his white pickup truck off a local freeway and onto the sandy roads that run through his SeaView orchard and into the groves.

“Buenos dias,” said Jensen, as he walked toward the workers and their foreman, stepping carefully over fallen fronds to avoid large palm needles and the occasional snake.

Here, on his 150 acres of date groves, Jensen is an observer. He watched the workers but didn’t say anything — in part because he doesn’t speak Spanish but also because he didn’t want to disrupt the chain of command.

Under shade from the palm fronds, workers in harnesses pulled white polyester mesh bags over each date bunch and tied them off at the top and bottom to protect the fruit until it is ready for harvest.

When that happens, most of the dates will be sorted, graded and packaged and sent directly to commercial freezers for next year’s Ramadan.

Although the date demand will be out of season for years to come, it turns out it is the ideal fruit to store in freezers for a year or more. Any changes to the fruit are more noticeable to the eye than the palate, including sugaring on the surface and skin breakage, Jensen said.

But the thought of year-old fruit remains unappealing and callers to SeaView insist on fresh produce. Some, unfamiliar with the ripening process, ask if the dates can be picked a few weeks early.

“The funny part is when they argue with you, ‘Why aren’t they ready?’ ” said Roya Jensen, Dennis’ wife, who oversees sales. “Because every year they’re ready in September.”

Growers including the Jensens have been dealing with the supply-and-demand crunch the last few years, with harvested dates rushed from the groves straight to markets. This year, growers have had to rely on last year’s crop going into the season.

In January, SeaView sent its annual Ramadan shipment to Malaysia as well as to France. In years past, the company has sent dates to Saudi Arabia and United Arab Emirates.