The mews was built in the 19th century. A 2012 English Heritage report described the six-acre site as "a garden of great national importance", but highlighted many areas that needed restoring.
Bartholomew managing director Barry Burrows said the residents take great pride in being custodians of the historic site and want to restore the gardens to "something of their former glory". But they are pragmatic about the costs involved.
"We have looked at preparing a cost-effective schedule on reviving, improving and maintaining the gardens over the next few years," he added.
"Our intention is to use the report as a basis for the direction we take in choosing plants and deciding on the elements that would be most cost-effective and sensible to undertake."
After the terrace balustrade is renovated it will be draped in wisteria and the borders filled with plants described in the original plans. Overhanging branches will be cleared from the ravine and some trees removed to preserve historic faux rock structures.
Rhododendrons and ferns, more in keeping with the original design, will also be reintroduced. The silt-clogged lake has been dredged and aquatic and marginal plants chosen to improve water quality and encourage wildlife.
"We intend to introduce modern varieties of plants that would have been used in the 19th century that will have a better chance of thriving and establishing in the more challenging areas in the garden," said Burrows.