The gardens of Buckingham Palace are to be opened for public tours for the first time to raise money for their upkeep.The Queen has given her permission for the 39 acres of lawns, lake and flowers to be opened to groups from next spring.The £20-a-ticket tours could raise up to £70,000 a year to help pay for repairs and maintenance to the crumbling palace and its grounds.Next spring the public will be able to view Buckingham Palace gardens, the largest private garden in the capital.The private gardens, which are the largest of their kind in the capital, are the venue for the Queen's summer parties.Guy Barter, head of gardening advice at the Royal Horticultural Society, described them as an 'oasis in a sea of chaos and traffic'.'One isn't conscious of the city which is all around them, and the gardeners have cleverly planted wild species all around the perimeter, which insulates the gardens from the roar of traffic,' he said.'It is only when one looks up and sees the tops of tower blocks that one is reminded that the gardens are in the heart of the capital.''It is very much the Queen's private garden and that gives it an intimacy which is missing from the big public parks.'They give an insight into the person, a private world away from her very public life.'Tours will take visitors to the famous herbaceous border, the wisteria-clad summer house and the Rose GardenHe said that an oak tree has been planted for each of the Queen's children, growing from an acorn germinated on the day they were born.Buckingham Palace is the holder of the national collection of mulberries and there are almost 30 different varieties grown there.'But what might surprise people,' Mr Barter said, 'is that the gardens feel quite low maintenance, and are by no means extravagant.'The tours will be run only in April, May and June, and only when the Queen is not in residence. Numbers will be limited to 25 fee-paying visitors at a time.They will be given a half-hour talk on the gardens' history, including King James I's failed attempt to establish a silkworm farm in the grounds.They will then take a tour around the mile-long path past the herbaceous border, dug up for vegetables in the Second World War, the wisteria-clad summer house and the world-famous rose garden.The Queen, who has an estimated personal fortune of £320million, first opened Buckingham Palace's State Rooms to the public in 1993 to raise cash for the repair of fire-ravaged Windsor Castle, and they now attract more than 360,000 paying visitors a year.