The only National Trust property they don't want you to see

Secret site will protect at-risk plant species from disease

'This is the Trust's most important plant conservation initiative for more than 60 years' - Mike Calnan, National Trust head of gardens

A high security conservation centre to safeguard Britain's flora from the spread of new plant diseases is to be established at a secret location in the Devon countryside.

The two and a half acre National Trust site, which was opened yesterday, will see the emergency propagation of threatened specimens such as native oaks, wild asparagus and rhododendrons.

Described as the Trust's most significant conservation initiative for more than half a century, it will bring together under-threat items from 50 of the charity's major collections and all 200 public gardens. Staff will begin the task of logging all endangered plants across the Trust's properties.

Many of the specimens were brought back to Britain and raised from seed in gardens that have become major tourist destinations, attracting millions of visitors each year. However, only scientists and Trust personnel will be allowed to enter the new site situated in the east of the county in order to maintain tight bio-security.

New plants will be placed in quarantine units to ensure they are free of disease and do not infect the 12,000 specimens set to be developed at the centre at any one time.

Mike Calnan, head of gardens at the National Trust, said: "The National Trust's portfolio of plants is of immense importance and is one of the most significant collections in the UK. This is the most important plant conservation initiative from the National Trust for more than 60 years and will have a legacy for decades to come."

Scientists hope to create resistant replacements for species liable to diseases such as Phytophthora ramorum which causes Sudden Oak Death. First diagnosed in California in 2000, the disease has spread rapidly to Europe appearing in the UK in 2003. It can affect 40 different species including horse chestnut, viburnum and rhododendron. Among those to be preserved first are Rhododendron macabeanum from Trengwainton Gradens near Penzance, brought to Britain from India in the 1920s; Juniperus Communis from Compton Down in Dorset and rare Acer palmatum from Winkworth Arboretum in Surrey.

The Trust will also offer a propagation service to private growers looking to preserve rare species as well as offering training in conservation. Among recent successes are the creation of an eight-acre "Mother orchard" at Cotehele in Cornwall which helped save more than 300 different varieties of local cider apple.

The loss of native orchards in recent decades has resulted in the destruction of some of the South-west's richest eco-systems and the disappearance of hundreds of varieties. It is estimated that 95 per cent of cherry, pear, plum and apple orchards have been uprooted since 1950, resulting in the loss of valuable genetic material.

Two full-time members of staff and five volunteers will be employed at the new site. Volunteer Charlie Port, who worked for the National Trust at Knightshayes, which was previously responsible for the propagation of rare plants, said: "I've been involved with propagating plants for the Trust for 25 years now and we've had thousands of successes. I get huge satisfaction from the idea that some of the plants will be around for hundreds of years."