The double walled garden will benefit from the money

The money, which has been generated from landfill taxes, has been awarded by environmental charity Grantscape.

Last year, the garden was saved from serious financial problems when it was given a rescue package of over �1m.

Dr Rhodri Griffiths, general manager at the garden said the new grant was "excellent news".

"This is a superb example of the private and public sectors working together to ensure a bright future for our National Botanic Garden," said Dr Griffiths.

The garden was saved from closure by a �1m deal in 2004

"This shows the confidence the private sector has in the garden's importance as a national asset.

"The garden is really blooming, visitor numbers are up, all financial targets are being exceeded and these grants are an integral part of our success."

It is not the first grant given to the garden from Grantscape, which aims to help fund projects with benefit to the local environment.

Other awards included �265,000 which was used to provide environmentally sustainable treatment of waste water from the site and another grant of �400,000 which was also used at the double walled garden.

Grantscape's Steven Hargreaves said it was "proud" to be able to award the money.

The garden, which cost more than �40m to set up, hit financial difficulties in the years after it opened in 2000, and risked closure in the winter of 2003-4.

Carmarthenshire County Council, the Millennium Commission and the Welsh Assembly Government all contributed to the package which helped save it, and it has now celebrated its fifth birthday.