You can’t say no, the caller beseeched, in a mock-threatening tone best reserved for dear friends. “I’ve already volunteered your services,” the message continued.

Fortunately for umpteen thousands, Ellen Dubinsky said yes. Her golfing buddy and fellow volunteer, Nora Stern, had the skeleton of an idea: Start an all-Missouri Market with Dubinsky. Together, flesh out the details.

This year marks Missouri Botanical Garden’s 20th Best of Missouri Market, but it will be the last one co-chaired by Stern and Dubinsky. That colossal feat, as well as the enduring power of the women’s friendship, attests to at least three things:

First, the women are visionaries, according to many. Their shared focus on Missouri’s food producers, artisans and craftspeople pre-dates today’s impetus to “buy local” to promote sustainability and green living. Plus, their market has continued to attract some 25,000 buyers annually.

Second, volunteers like Stern and Dubinsky have become a rarity. “We’ve really had lots of fun, but we’re sort of antiques,” Dubinsky says.

She has served as president of the Garden’s member board. Stern held that position three times and also established the Garden’s membership desk, through which 6,500 members renew or enroll each year.

Stern likewise masterminded, chaired and/or made memorable glittering events such as the Garden’s “Rose Ball,” “Chrysanthemum Ball with Gloria Vanderbilt, “Centennial Gala with Bobby Short” and the Monet-influenced “Impressions of Giverny.”

For 20 years, Stern and Dubinsky have spent portions of 11 months annually, taking off only the month of December, to plan the Garden’s Best of Missouri Market.

Things are different today. Many women work. Some, who postpone childbearing to advance in their careers, find at-home responsibilities swelling, just when previous generations were increasing their community service.

Though Stern and Dubinsky never actually planned to remain market co-chairs for so long, each had decided to serve as long as the other did. And that brings us to the third thing that these good friends share, agreeing it’s time to move on. Or, as Dubinsky puts it, “You gotta know when to go.” Both now grandmothers of four, they wish to remain active at the Garden and plan to attend, as something of a spectator, upcoming markets.

Still, it is not surprising that as their successors, the Garden has tapped two already salaried Garden employees, Lynn Kerkemeyer and Chelsea Harris. Both have on-the-job experience in planning and managing events. The 21st-century reality is that without pay, Stern and Dubinsky would likely be irreplaceable.

Finally, at a time when failures make headlines, it’s refreshing to note that from a simple aim – namely for the Garden to attract people who “weren’t just lovers of daylilies or cactus or ferns,” Stern recalls – a signature event can blossom.

Though perhaps not without a few thorns.

The market’s first year, the Sunday-only event for some 35 mostly low-profile food vendors, was kicked off with a country-western dance on Friday night. Not a good idea, Stern and Dubinsky realized.

Besides needing to dismantle the Western-style setting, they spent all day Saturday hauling vendors and their products, one vendor at a time in a golf cart, uphill to the two tents where the Garden’s market was scheduled.

In the future, the women vowed, the market would be a weekend-long selling event. No cowboy hats or fringed skirts needed. (This year’s market includes a Friday night of selling.)

Looking back, the co-chairs say, there were times when their positivism may have unduly influenced sellers. Early on, a TWA agent – who spent his off-hours perfecting marinades – brought enough boxes of his product to last for a month. Market-goers could barely see him within his display. Yet he managed to sell every last bottle.

Since 2000, when figures are available, Best of Missouri Market has attracted about 230,000 people total.

To date, the market has raised almost $4 million for the Garden. Money comes from booth fees, admission tickets, Garden memberships sold, ads in the program book and sponsorships.

Commerce Bank has been a sponsor from the market’s inception. Schnucks is a longtime lead sponsor.

In the last 16 years, again according to available figures, in excess of 15,000 memberships to the Garden have been sold during the market.

Unlike some markets, Best of Missouri takes no percentage of vendor sales. Rather, many vendors are encouraged to showcase their more reasonably priced goods. For someone like a skilled blacksmith, private commissions for costlier, hand-forged fireplace screens may then follow.

With food vendors in particular, success at the market has sometimes proved a double-edged sword for the co-chairs. Supermarkets often scout Best of Missouri for new products to stock. So do other fairs and festivals, many of which did not exist when Best of Missouri began.

And widespread exposure, plus booming demand, may mean that vendors – including those who owe at least part of their bottom-line health to Best of Missouri – no longer have the time or manpower to staff the market at the Garden.

Still other vendors, not always invited back after years of success, have felt miffed, due to what Stern and Dubinsky say is a misunderstanding of the market’s aims.

In extra-popular categories such as jewelry making, the co-chairs explain, they have attempted to keep introducing or rotating in, new or not recently seen vendors. This year, the women have selected 30 new sellers, to be among the approximately 130 vendors of food and art/crafts.

Vendors in 2011 will continue to share four massive tents. But in response to the surveys of buyers and sellers the co-chairs routinely conduct, many sellers will be limited this year to one booth instead of two, to provide more walking space.

Samples, too, remain something of an issue. A taste is a taste. Too-generous vendors need not give away their inventory, the women advise. A food court, where market-goers can buy actual meals, has been another market innovation.

However, could it be that after all these years, the co-chairs are “innovated-out”? Not a chance. If they could figure out the logistics, they would offer valet parking on Saturday and Sunday at the market. But then again, maybe some things need to be left to the next generation.

Best of Missouri Market

WHEN: 9 a.m. to 5 p.m., Saturday and Sunday. From painting pumpkins to milking cows, many activities for kids, included in the admission fee.

WHERE: Missouri Botanical Garden

NEW THIS YEAR: “First Look Friday,” from 6 to 9 p.m. on Friday. A chance to beat some of the crowd and shop early. Valet parking available. To commemorate the market’s 20th year, volunteers will draw names for more than 20 gifts.

COST: On all three days, $12 for adults, $10 for those age 65 and older, $5 for Garden members and children ages 3 to 12. Kids under 3 are free.