A private conservancy will take over day-to-day operations of the Rose Fitzgerald Kennedy Greenway later this month under the terms of a five-year lease signed with the Massachusetts Turnpike Authority.

The lease calls for the Greenway Conservancy, which relies on a combination of state aid and private donations, to pay the entire cost of maintaining and operating the park that snakes for more than a mile through the heart of Boston above the Central Artery. The Turnpike, which built the park after the elevated highway cutting through Boston was torn down, is struggling with a heavy debt load and a deteriorating road system, and is eager to shed responsibility for the park.

Under terms of the lease, which expires December 1, 2013, but can be renewed by mutual agreement, the Turnpike is not required to provide any additional funding for the Greenway. The Turnpike, however, agreed to provide maintenance and parking facilities for the Conservancy at Pike-owned properties located at 185 Kneeland Street and 128 North Street.

The Conservancy board unanimously approved the lease Monday night and then voted to pay Work Inc. of Dorchester $450,000 a year to handle basic landscape and maintenance for the park. Work Inc. will be paid separately for snow removal. Greenway officials said they plan to supervise Work Inc. employees while handling all horticultural work at the park. The total maintenance and horticultural budget, including the Work Inc. contract, is expected to be $2.2 million a year, close to half of the Conservancy’s overall $5 million budget.

The Greenway Conservancy has received $15 million in pledges from private donors and another $5 million from the Turnpike Authority. Lawmakers last year agreed to provide another $2 million plus half of the Greenway Conservancy’s budget — up to a maximum of  $5.5 million — through 2012, but the funds were contingent on surpluses and interest earnings in state accounts. The $2 million disappeared in the economic downturn and the matching funds have dwindled dramatically, but state officials have scraped together about $3 million for the coming year.

Even with money tight, Greenway Conservancy officials indicated at the board meeting that they may part ways with the Massachusetts Horticultural Society, which has spent close to $800,000 planning, planting, and maintaining gardens on the three parcels near South Station.

The Horticultural Society once had ambitious plans for a garden under glass on the Greenway, but financial problems killed that initiative. Horticultural Society officials subsequently entered into an agreement with the Greenway Conservancy to build a series of gardens on the parcels near South Station, but that agreement would be nullified by the lease with the Turnpike. Horticultural officials said they were prepared to continue maintaining the gardens they built last year, but the Conservancy’s executive director, Nancy Brennan, made no promises other than to say she would meet with society officials.

“I was totally flabbergasted,” said Joe Kunkel, the interim managing director of the Horticultural Society. “It’s pretty clear they don’t want us there. They want to take over the property and do something different. They said they’ll meet with us, but the handwriting is on the wall.”

Some members of the Conservancy board apparently had concerns about the financial terms of the lease. Charles Baker, the chief executive of Harvard Pilgrim Health Care and one of the Conservancy’s board members, said he had considered voting to reject the lease with the Turnpike but ultimately concluded approval of the lease was in the best interests of both the park and the Turnpike. He said the Turnpike needs to focus on its financial problems and the Greenway needs a full-time overseer who can take care of the park and raise money for it. Still, he said, the Greenway Conservancy’s job won’t be easy.

“Private fundraising in this environment is going to be brutal,” he said.

Greenway photo by Frank Curran.