NEW YORK — Fresh is fresh. The word is everywhere, plastered all over food-market labels.

Then there’s “picked from the vines on the roof and taken downstairs to sell in the store” fresh. That’s hard to top.

Can you call it “grass-roots” farming when the roots flourish several stories above the busy Manhattan street where Eli Zabar’s upscale food store, the Vinegar Factory, is located?

Is it literally down-to-earth gardening up there, with high-rise buildings all around the vegetable patches? Yes, there they are, lusty plants firmly rooted in earth, basking in more sun than you’ll see in the narrow street below.

Tomato vines are heavy with the eccentric shapes of heirloom varieties, some red ripe for the picking, others still streaky green. Honey-sweet figs cluster on leafy branches next to long plots of baby salad greens and tubs of herbs.

Zabar established his rooftop garden some 10 years ago, he says. “What motivated me to set up the garden was that, especially in the summer, we go to Europe, to France, and I’m always inspired by the quality of the produce in the markets I see there.”

He concluded that to get enough produce of comparable quality he’d have to try growing it himself. “Here in the Northeast, since the growing season is really so short, I’m hardly able to get all the vegetables I want.

“My original thinking was to grow tomatoes,” he explains. “It occurred to me that I have all this real estate, all this space up here — and there’s the heat from the ovens, our bakeries down below.”

One factor was that the city itself has a microclimate. “I was acutely aware that Manhattan in midwinter is appreciably warmer than the surrounding areas. And the kitchens and the pastry shop of our bakers were throwing away heat in the air. Why not make it do some good?”

The natural season for tomatoes in this region would be mid-July to mid-September. Zabar’s idea was to extend the season with rooftop greenhouses. People suggested he could grow tomatoes hydroponically, he said. “But I strongly believe that flavor comes from the soil itself, and I also believe in sustainable agriculture."So he built one small greenhouse as an experiment. “It’s a very humbling experience being a farmer,” he says, pointing out that, cultivating his crops, he doesn’t think of himself as simply a gardener. “That first season I got a lot of plants growing — but not a single tomato.”

The first greenhouse was just a simple hoop shelter. Zabar persisted with his tomatoes, then added lettuces to his range. That has worked out well, he says. They grow baby-size lettuces and salad mixes year-round, cut by hand with scissors after about two weeks’ growth.

Tomatoes are very temperamental, especially heirloom varieties, with specific needs that prompt them to flower and give fruit, he explains. “Lettuces are more forgiving. Greens and other salad vegetables grow more easily all year round: That was a real discovery.”

Zabar says his aim was the same as with the tomatoes. “Whatever I did I wanted to do better than what was generally available. I found we could grow all types of lettuce and salad greens and harvest them early when they taste better, then send them right downstairs to be sold — no shipping needed.”

Their rooftop produce is dubbed natural, because it is not officially certified organic although Zabar says all the materials and composting they use are organic and pesticide-free.

The total area under cultivation on two roof spaces, one over the Vinegar Factory food store and the other just across the street, is some 22,000 square feet, about half an acre, Zabar says.

Right now in summer, some potted tomatoes and other plants are also grown out in the open; under cover in the greenhouses there are lettuces all year round, tended by two full-time gardeners. At this season they’re harvesting 40 to 50 pounds of tomatoes a day, and six or seven 2-foot-long baskets of baby lettuce.

They also grow herbs and sometimes flowers. Figs are doing well, and now they’re trying high-rise raspberries with good results.

Before this rooftop venture, Zabar says, he hadn’t been into gardening in a major way, although he says he knew a lot about gardening and farming in theory, and he’d tended a little Elizabethan herb garden out in Nantucket.

Now he goes up to putter around at least every couple of days, all times of year. “But the best time is winter,” he says, “when it could be around 25 degrees outside. It’s an oasis of peace, it has the smell of the soil and the plants. It’s like yoga, so calming and peaceful and beatific.”

His heirloom tomatoes, grown for their flavor, really do reward a taster who bites into them. “Since we are harvesting the tomatoes just for ourselves, we can let them get really ripe. No grower who has to ship them can usually wait till that point.”

Customers pay a premium of around $10 a pound.

What’s his favorite way to eat these perfectly ripe tomatoes?

He says they are on the family table all the time, in season. “I enjoy the tomatoes just plain, cut in quarters or slices,” he says. “Their difference from ordinary tomatoes is like night and day.” All that the best summer tomatoes need, he says, is olive oil, a little salt, and red-wine vinegar.

Warning: Tomatoes should never be refrigerated: “They suffer terribly in refrigeration,” Zabar says.

Then, pursuing the idea of summer salad, he volunteers his version of “a very nice salad dressing for greens.”

Start with a clove of garlic, mashed up with salt and pepper. “Then you mix olive oil and red-wine vinegar, in the proportion of 3 tablespoons of oil to 1 tablespoon vinegar and pour that on top of the garlic that you have mashed up. That proportion is really delicious and it makes the lettuce taste really good.”

Zabar, 63, is a son of the founders of Zabar’s, the Upper West Side landmark food emporium and delicatessen. Eli Zabar struck out on his own more than three decades ago, and now runs his own food empire, including three stores, cafes and a bakery on the Upper East Side.

The Vinegar Factory was once exactly that. The old industrial building adapted for the current store still has some of its original architecture, and a few of the huge old vinegar barrels are used as food display stands in the store.