FARMINGTON – Nancy Knapp has a green thumb.

Almost everything she plants flourishes. She also has a husband, Burt, who shares her passion for gardening, good nutrition and healthy living.

Take the couple, a farm dating back to the 1700s, a quarter-acre planted with a variety of vegetables and berries – and the bounty needs to be shared.

Last year, they gave the extra produce to neighbors and the local food pantry. This year, they offered community-supported agriculture shares to people who wanted to buy into their Porter Hill Farm crops.

CSA participants buy a share of the crop in the spring when farmers need extra cash to buy seed, Nancy Knapp said. Different farms offer different arrangements for purchasing CSA shares. Some offer payment plans for members.

At the Knapps’ farm, a shareholder comes once a week for 14 weeks to pick up a bag of fresh-picked organic vegetables.

One recent bounty included broccoli, chard, beet greens, lettuce, peas and herbs. The couple also plans to add a little homemade maple syrup, Burt said.

The Knapps plan to expand their CSA to include more berries and eventually, flowers. Some farms offer meat and dairy products. Some even allow people to work for produce. Full- and half-shares are usually available for purchase near the beginning of the growing season.

Interest in CSA is growing, said Melissa White, the organic marketing director for the Maine Organic Farmers and Gardeners Association.

CSAs in Maine increased from 75 in 2006 to 115 this year, White said. Much of that growth is from increased consumer demand but also because the model of how a CSA works has been established and is more easily understood by local people, White said.

About 4,000 Maine families belong to CSAs, she said.

The number of farmers markets has also grown from 55 in 2003 to 75 this year.

“People are obviously seeking out more local food,” White said.

A full share in the Knapps’ crop will feed about four people and costs $400. The Knapps also sell half-shares, which was what Monique Claverie of Farmington bought.

“My husband and I grew up in families that have gardens but we live in town where there is no land for a garden,” Claverie said.

A half-share for the couple and their young daughter has provided more than they thought it would, she said.

“Most farmers provide 110 percent (value) for the share,” said Burt Knapp. “But there is a risk, if the crop doesn’t do well. But you get to know your farmer and what he is doing.”

The CSA introduces people to vegetables they may not have tried and assures farmers a market for their produce, he said. Many CSAs also offer recipes with each week’s share.

The Knapps, both doctors, live a mostly vegetarian lifestyle, grow much of their own food and are passionate about what they eat.

“We both understand and know what good nutrition is and want to share the health benefits,” Nancy Knapp said.