Batsford Arboretum is undergoing work that its trustees hope will double visitor numbers over the next five years.
Development includes a new entrance building comprising a visitor centre, cafe, shop and plant centre. Another 3ha are also being added to the 28ha site, following a land swap deal with the privately-owned Batsford Estate.
Tony Russell, former head forester at the nearby National Arboretum at Westonbirt, is on the Batsford Foundation charitable trust's board.
He told HW he was "extremely excited" to see the project start to come to fruition after several years of planning. "We have been working towards this project for about four or five years," he explained. "Over the years the Batsford Foundation has accrued the money for investment so we are not involving any outside grant-giving body."
He added that was a positive move because it meant there was not the need to achieve objectives required by an external organisation. "Our objectives are specifically conservation and education but we have had very limited facilities in the past," said Russell.
"We will be able to give lectures and have schools come in. Our plan is to double our visitor figures over the next five years to about 120,000 a year."
Batsford Arboretum was created in the late 19th century by Lord Redesdale as a woodland garden with Japanese influences.
After the Second World War the second Lord Dulverton developed and expanded the arboretum and opened it to the public. In 1983 he set up the Batsford Foundation to manage the arboretum after his death and to ensure long-term public access to the collection.
The buildings have been designed by architects John Falconer Associates working closely alongside landscape architecture firm Portus & Whitton.
Landscape architect Martin Portus said the wider landscape would be "going native". Screening Leyland Cypress are being removed and oak woodland will be planted around the car park.
An avenue of trees - mountain ash or whitebeam - will also be created at the plant centre. Beam Construction (Cheltenham) is carrying out the work and the new building and facilities are expected to be open by Easter 2011.