Registering a botanical garden , What i think is , you have to contact local govt office for details information. I was visiting a botanical garden in Shanghai, China that is Shanghai Botanical Garden , details bellow :
http://photo.makorsha.net/thumbnails.php?album=20
They are registered in Shanghai local govt.
Thank you
Aburi Botanical Gardens was created in 1890.
Benalla Botanical Gardens was created in 1886.
Botanical Gardens of Tirana was created in 1964.
Gisborne Botanical Gardens was created in 1874.
Arenal Botanical Gardens was created in 1991.
Aarhus Botanical Gardens was created in 1875.
Auburn Botanical Gardens was created in 1977.
Ballarat Botanical Gardens was created in 1857.
The Botanical Register ended in 1847.
The Botanical Register was created in 1815.
Some of the best botanical gardens in the world are Kew Botanic Gardens in London, Royal Botanic Gardens in Sydney, Singapore Botanic Gardens, and Kirstenbosch National Botanical Garden in South Africa. Each of these gardens is renowned for their extensive plant collections, beautiful landscapes, and important conservation efforts.
Royal Tasmanian Botanical Gardens was created in 1818.