A new show at RHS Hyde Hall gardens in Essex will take place on 13-15 August. The Shrewsbury Flower Show, established in 1875, is on 13-14 August, with Chris Beardshaw and the Hairy Bikers lined up as star guests.
Visitor numbers were once 100,000 but are now nearer 60,000. Around 60 nurseries will be at Shrewsbury, with 30 expected at Hyde Hall.
Alan Titchmarsh officially opened a £3.5m visitor centre and car park at Hyde Hall last month. The RHS wants the Hyde Hall show to be similar to the new outdoor nursery exhibitor show at Wisley, held in September 2009 and on again on 10-12 September this year.
RHS acting director general Gordon Seabright, speaking at RHS Cardiff Flower Show, said: "We've done so much at Hyde Hall we want to get more people to see it.
"Last year's Wisley show attracted 27,000 visitors and we see Hyde Hall as similar to that. The area round the new visitor centre to the top of the hill is made for trade stands. There's not enough RHS in the east of England. No impact on other shows is an important consideration."
The RHS has sent 300 potential exhibitors a questionnaire about the show. Peter Road-Night, secretary of Shropshire Horticultural Society, said: "We're in discussion with the RHS. Our dates are set a long time before. Exhibitors will need to decide which show to support if Hyde Hall happens."