Heavy rainfall on the day before the show resulted in flooding and a last-minute change to the location of the car park for visitors to the show, held at Roundstone Nurseries near Chichester.
Exhibitor Simon Davenport of Hollyacre Plants said: "The show is very nice and obviously get's a lot of support locally but the numbers are down. It could be for a number of reasons, but the news said that there was trouble on the roads out of Chichester which does not really help at all."
Kings Seeds business development manager Ian Riggs said it would have been "more encouraging" to see more visitors to the event but added: "with all shows it's not about the quantity but the quality of the visitors".
He said: "It might have been the bad weather yesterday that put people of - there were floods everywhere."
Exhibition organiser Monro South's sales manager Kieran Daly said: "Without a doubt, severe weather warnings around the Chichester area may have had an impact on visitor numbers, but we are pleased that once again Southern Growers at Roundstone has proved to be a success.
"The early indication we have had back from exhibitors is good and the tours and seminars were well attended."