Horticultural shows had taken place in Brighton and Hove for some years in the 19th Century. This report from the West Sussex Journal dated 1st September 1891 indicates that one was taking place in the Portslade area for the first time.
This article from The Worthing Gazette,
dated 4th September 1895, indicates that it was now known as the Aldrington, Portslade and Southwick Flower Show and had become a two day fixture.
A comic postcard from the time.