Last month at Union Square Greenmarket, organic farmer Keith Stewart added a provocative new item to his bucolic spread of glistening Hudson Valley greens and earthy rocambole garlic. The author of It’s a Long Road to a Tomato started selling something Greenmarket shoppers are accustomed to getting for free: the flimsy plastic bags that hang from every stand in landfill-clogging profusion. “I’m something of an environmentalist, and I felt guilty,” says Stewart, who could no longer reconcile his sustainable, Earth-friendly lifestyle with the country’s 100 billion–per–year plastic-bag problem (and the 40,000 he estimates his own customers go through). By charging a nickel a bag (“a slight punishment,” Stewart calls it) and offering a variable credit (up to 25 cents) to those who bring their own bags, the Orange County farmer has somewhat surprisingly emerged as the market’s anti-plastic pioneer. Although Greenmarket encourages shoppers via fliers to bring reusable bags and sells tote-bag alternatives for $2 and $10, Stewart thinks it could do more. “There should be a market-wide policy,” says the farmer, who invested in about 40 shopping baskets to help his customers collect their purchases before paying for them. “I think what Keith’s doing is a terrific thing, and we’d like to see it spread,” says Marcel Van Ooyen, executive director of Council on the Environment of NYC, Greenmarket’s parent organization. “But we have 180-odd different vendors, and we’d want everyone to feel that they’re involved in the decision-making process.” It’s not just Greenmarket, according to Stewart, that’s yet to institute an incentive that might make a difference: New York City, despite Mayor Mike’s ambitious PlaNYC, is actually lagging behind the shopping-bag curve. San Francisco banned the nonbiodegradable offenders last spring, and several European countries have long taxed their use. And Bloomberg, who boldly took on smoking and trans fats, has been uncharacteristically mum on the plastic-bag blight, other than the administrations’s obvious “tip” to “bring your own cloth bag to the grocery store.” Even out-of-state interlopers and Union Square Greenmarket neighbors Whole Foods and Trader Joe’s offer better incentives: Whole Foods credits bag-abstaining customers ten cents for bringing their own, and Trader Joe’s distributes raffle tickets, with winners entitled to $25 of free groceries. As far as Keith Stewart is concerned, raising his customers’ consciousness is just as important as assuaging his own guilt. “The response has been overwhelmingly positive. The number of people who bring their own has probably quadrupled.” But even the best intentions are sometimes sabotaged by ingrained habits. After ringing up a promotional tote benefiting City Harvest at Grand Central Market last month, the clerk packed it up—in a plastic bag, of course.