The offer is part of a new pricing scheme that aims to make both gardens more accessible to people of all ages and incomes.
Visitors can pre-book at www.kew.org or pay £1 on the gate.
“We are really delighted to be able to offer more people a chance to experience the wonder of Kew and Wakehurst,” said Richard Deverell, director of the Royal Botanic gardens, Kew.
He added: “We know what a wonderful thing it can be to enjoy a day out in nature and to explore the many corners of our gardens, take a picnic, listen to the beat of the wildlife and learn about the fascinating origins of some of our plants, many of which are extinct or threatened in the wild.”
It is the home of the Millennium Seed Bank and has 535 acres of native temperate woodlands, meadows and wetlands, as well as spectacular views of the South Downs.