Some £55,000 has been spent on plants, flowers and trees for the Downing Street garden over the past five years.
But the Royal Parks, responsible for the half-acre plot behind the Prime Minister's famous residence, has not disclosed details of staff and other maintenance costs.
The walled garden features an L-shaped lawn, flowerbeds and a pond, as well as a vegetable patch and play area for the Camerons' children.
The garden has been used to stage a barbecue for US president Barack Obama and wife Michelle, and hosted the first coalition press conference with Mr Cameron and his Liberal Democrat deputy Nick Clegg.
Mr Cameron handed one of the long-serving gardeners, Paul Schooling, a British Empire Medal (BEM) in the recent dissolution honours.
In response to a freedom of information request from the Press Association, the Royal Parks released details of "significant" plant, shrub and tree outlays since 2010.
In 2010-11 £10,843 went on "seasonal bedding", while in 2011-12 the figure was £9,309, in 2012-13 £11,768, in 2013-14 £8,812, and in 2014-15 £6,733. Another £7,339 was spent on shrubs, perennials and trees over the period.
However, the agency did not supply further information requested on staffing and other costs - saying that since last year those expenses had been covered by a wider contract for maintaining nearby St James's Park and Green Park.
The overall value of that contract is around £1 million a year, according to tender documents. The Cabinet Office previously released maintenance costs for the Downing Street garden, but has not done so since 2011-12 - when they said the annual bill was £47,321.
Jonathan Isaby, chief executive of the TaxPayers' Alliance, said: "Given the pressure on the public finances every bit of care must be taken to make sure costs don't grow out of hand. Every single penny of taxpayers' money should be carefully spent."