Little is known of the early history of the gardens, but it is assumed from the great age of many of the specimen trees that they were laid out at the time the mansion was built. It is possible that at least part of the gardens existed prior to that date, since the former mansion house, known as Old Mertoun House – now the head gardener’s house in the walled garden – dates from 1677 and nearby is a well preserved, circular dovecot dated 1567, thought to be the oldest in the county.
The gardens have been run since 1984 by a Charity called Mertoun Gardens Trust and lie to the north and east of Mertoun House extending to about 26 acres. The soil is a medium loam, slightly acid, overlying sandstone and, since the gardens are well screened by mature trees in all directions – particularly from the cold, easterly winds a great variety of species have been established and now flourish.
To the north-east of the house is a wide expanse of sweeping lawn, bounded to the east by the tree-covered bank of the Tweed and to the north by borders of herbaceous plants, shrub roses and azaleas. Beyond is an arboretum, established over the last 60 years, with a great variety of both conifers and hardwoods. Paths and grass walks provide access to all parts of the garden and its surrounding woodland, as well as forming several most attractive circular walks, with views over the River. Bridges cross the Maidenhall Burn which runs through the garden into the Tweed.
Mertoun Kirk stands within the grounds, but it is not open to members of the public except for Church Services.
To the north is the Walled Garden of about three acres, in which is situated Old Mertoun House, 1677. On a south-facing slope, it contains a great variety of fruit trees, vegetables and flowers and is immaculately maintained. There is a range of heated greenhouses, and cold frames. Visitors are asked to respect the privacy of Old Mertoun House, and not to enter the greenhouses.