harvest a few long-pig and see if that deters the crop-theft problem...,

Boston | William Anderson, like a growing number of urban farmers in Boston, doted on his small plot near Codman Square over the summer, sowing seeds, watering regularly, clearing weeds, and watching with pride as the sprouts slowly blossomed into turnips, bell peppers, and other hearty vegetables.

Then, as he prepared to harvest the broad leaves of his collard greens, he was dismayed to discover about 15 of his plants decapitated, all the tasty leaves pilfered.

“It was just depressing to see,’’ said Anderson, 69, who planned to share the fruits of his labor with friends. “I was hurt. I had nursed them, watched them grow, and someone took advantage.’’

It is an increasingly familiar lament across the city, where there are some 3,500 plots in about 150 community gardens. With everything from cucumbers to watermelons ripening in the open, the gardens are something like a supermarket without doors, effectively free for the picking.

“It’s a problem that has worsened with the economy,’’ said Paul Sutton, coordinator for open space and director of urban wilds at the Boston Parks and Recreation Department, which oversees five community gardens. “I hear about people picking tomatoes and squash in the middle of the night. It happens all the time.’’

Theft from urban gardens peaks at this time of year, as the fruit and vegetables reach their final stages, sizable prizes waiting to be harvested before the first frost.

Veteran urban gardeners learn what not to plant and how to veil what they do grow. Valerie Burns - president of the Boston Natural Areas Network, a nonprofit that oversees more community gardens than any other organization in the city - has found that the bounty of mature eggplants and butternut squash are like bait for vegetable thieves.

After hers were swiped at a garden along the Southwest Corridor, she stopped planting them.

“You have to be philosophical about it if you garden in the city,’’ she said, noting that a fellow urban farmer found six cabbages for sale at a bodega that he suspected were stolen from his plot. “You just have to hope that it’s going to be food for someone who might really need it.’’

Betsy Johnson, president of the South End/Lower Roxbury Open Space Land Trust and a board member of the American Community Gardening Association, said the bigger the fruit or vegetable, the more likely it is to be stolen. She said pumpkins and beefy tomatoes are more enticing than spinach or Swiss chard.

Her organization issues tips to urban gardeners that include avoiding growing the more tempting vegetables and fruits at the edge of gardens and veiling them in the thicker foliage of less popular plants. She and others counsel gardeners to harvest as soon as possible.

“It’s a fact of life, but if it was so serious a problem, community gardens would have died out a long time ago,’’ Johnson said. “Instead, they are thriving.’’