"I never quite believed it was going to happen and, even when we had finished, the whole team was quite in awe,'' said the 32-year-old Ground Force presenter as she left South Africa yesterday, still picking the earth of Qunu, Mr Mandela's native village, from beneath her fingernails.
The former South African president, known as much for loving women as gardens, apparently thought Ms Dimmock, known as much for her cleavage as her gardens, "looked like one of the Spice Girls".
Mr Mandela, who spent 27 years in jail, mostly in a limestone quarry on Robben Island, is said to have fallen in love with gardening in 1988 when he stayed in a warder's lodge at Victor Verster prison near Cape Town during negotiations with the apartheid government.
His new garden - created for a 2 January special programme on BBC1 - features the strelitzia "Mandela's Gold" but not the protea, which is the national flower of South Africa.
The surprise element of the show was made possible by Mr Mandela's wife, Graca Machel, who invited the crew to do their makeover during a three- day absence by Mr Mandela.
Ms Dimmock said: "We aimed to create a shady, quiet area for him outside his study. There is a water feature, tiling, wall paintings, and pots made by disabled people in the area.''
Qunu, where Mr Mandela was born in 1918, is a hilly, rugged, windy region of the Eastern Cape. "The locals were great," Ms Dimmock said. "They came and helped us, cooked lunch and were very interested in what we were doing."
She said that when Mr Mandela returned from his trip to the United States, he was "really surprised, which was smashing. He was lovely and sweet, just like a grandfather."