It will take three days to set up the arrangements of the central part of the basilica including the Bernini's baldachin, the pair told the press in Ljubljana on Tuesday before leaving for Italy.

Flower arrangements will measure over 60 metres in length all together, said Sabina Šegula and Peter Ribič, who began cooperating with the Holy See a few years ago when they asked to be allowed to watch florists decorate the immense cathedral.

Šegula and Ribič were eventually entrusted with decorating some parts of the basilica, which has gradually grown into an annual cooperation between the Holy See and the Slovenian florists. Last year, they decorated the basilica for Christmas, while this will be the fourth time that they are decorating it for Easter.

Vatican gardeners do not interfere with their work, however the florists are obliged to uphold the tradition, which for instance dictates that only the colours of the Vatican flag must be used in the arrangements.

"There is no room for mistakes, everything must be perfect," Šegula said as she explained that they need to follow the cathedral's history and Renaissance style.

Additionally, each year Šegula and Ribič get to decorate other parts of the Vatican, where more creativity is allowed, Ribič said.

So far, they have decorated the chapel in the Apostolic Palace, the pope's private chapel and even the central loggia, where the pope usually gives his apostolic blessing during Easter and Christmas celebrations.

Šegula, who has a PhD in agronomy, and Ribič are valued experts in their field. They teach at the Naklo Biotechnical Centre, which covers secondary and tertiary educational programmes as well as research in agronomy.