The Swiss Garden was created within Old Warden Park in the 1820s by Lord Ongley and embellished by industrialist owner Joseph Shuttleworth in the 1870s, but had become overgrown in the 20th century. Old Warden Park is now owned by the Shuttleworth Trust.
Now it is being rediscovered thanks to a £2.8m Heritage Lottery Fund grant that will see the garden's 13 listed buildings and ornamental structures restored along with £400,000 worth of landscaping work by Hortech, with Haydens appointed as arboriculture consultancy on the project.
Principal consultant Chris Burnett said the key to the design was the balance between space and enclosure, light and shade and the many buildings and ornaments as well as the foliage.
"Were putting in 20,000 trees and shrubs, taking several out and clearing existing rhododendron," he added.
"The challenge was managing the transition between what it had to become and what it was going to become. We took out a lot of existing vegetation. A lot of that was mature yew trees. We've discovered a lot of shrubbery that was never intended to grow to maturity."