Kew Gardens, for those who don't know it, is formally the Royal Botantic Gardens, Kew, in Southwest London. It is a vast expanse of gardens and trees and greenhouses (many of them Victorian) conserving and sharing plants from all over the world-- rather like a plant zoo, really. It's an absolutely magnificent place, elegant and astonishing and great fun. When I was there on a sunny Saturday this February it was full of children and photographers. I'd reccomend it to anyone visiting London (their website here!)
In the 20s and 30s they evidently thought it was the cat's meow too, and London Transport put out loads of utterly gorgeous posters promoting it (it is easily accessible by Tube). The natural aspect leant itself so well to bold graphic design, even abstraction, and oh, aren't they swell?
From the collections of the London Transport Museum (and, again, I do apologize if the links have changed; their site tends to do that! Searching 'Kew Gardens' in the poster section will lead to all of them if necessary).
The Palm House, one of Kew's beautiful Victorian greenhouses full of tropical trees. 1926. Source
Bluebell time (about now, I believe). 1931. Source
Daffodil Time. 1923 Source
Sadly it costs a bit more than that these days. 1937 Source