More than poinsettias are ready to bloom at the Buffalo & Erie County Botanical Gardens.

So is the latest offshoot of the multiyear master plan: construction of a $4 million administration building and adjoining greenhouses.

Shovels went in the ground Wednesday to start the roughly 18,000-square-foot expansion on 3.14 acres of city property between the county-owned conservatory’s north side and the South Park Bog Garden.

Erie County Executive Chris Collins lauded the project, which will take about 10 months to complete, as another example of the public and private sectors working together to improve a local cultural treasure.

Other city and county officials and Botanical Gardens leaders were equally effusive. Even Collins’ recent rejection of the Botanical Gardens’ bid for $322,500 in 2010 operating support couldn’t spoil the fun.

The brick office structure and the growing houses—each with about 1,700 square feet of floor space — will be built with $2 million from the county as part of a $9 million, multiyear commitment made in 2004 to help restore and improve the century-old landmark designed by Lord&Burnham Co. The Botanical Gardens is raising $11 million privately to implement the master plan.

The move to the new building will free up the present administrative offices in a garage behind the glass-domed atrium building for expanded exhibition space, and the greenhouses will add much-needed year-round growing capacity.

The path for the new facilities was cleared in February, when the city granted a 50-year easement to permit construction on the historic South Park footprint.

Without the easement, county money could not have been spent on the city-owned parcel. The transaction was eagerly endorsed by the Buffalo Olmsted Parks Conservancy, which maintains South Park and other city parks and parkways designed by Frederick Law Olmsted.

Site work on the expansion had begun days before the ceremonial ground-breaking.

“We needed to get this thing kicked off,” said James Tilley, Botanical Gardens interim executive director. “We have to get as much of the foundation in as we can before the weather turns.”

The project follows completion of a 46-car parking lot on the parcel that gives visitors who formerly had to park along the South Park ring road quicker access to the indoor gardens.

The administration facility will be the first county building to conform to national Leadership in Energy and Environmental Design standards. Architect Bryce T. Bixby of Foit-Albert Associates is project manager, and Thomas M. Mc- Pherson of URS Corp. is engineering consultant.