The new area is designed to be visitor friendly in all but the worst weather and has been two years in the making. It contains 10,000 new plants and covers about half an acre.
A specially planned route through the garden, avoiding steps and muddy grass, will also open to visitors until 1 March. The garden was previously closed between mid-November and February.
Head gardener Troy Scott Smith said: "It’s a chance to see the garden in a whole new light. Gardens take on a new life during the colder months and I think people are starting to recognise the attraction of seeing them at this time of year".
"Visitors still want to enjoy the fresh air and open spaces we can provide, and are realising that there are many plants to enjoy – early flowering bulbs, winter flowering shrubs and plants with beautiful coloured stems or attractive bark. In previous years we have recorded over 50 plants that are regularly in flower on New Year’s Day."
Mince pies and punch will be served every day until the New Year and a warming brazier has also been installed in the coldest part of the garden.