The 2021 Chelsea Flower Show, which would have taken place between 18 and 23 May, has now been moved to September 21-26.
It is hoped that in September millions more people will have been vaccinated so mass outdoor events will be able to go ahead safely, with 140,000 predicted to attend over six days.
Ticket holders will be contacted by the RHS about options for a refund if they cannot attend in September. Thousands of people have tickets bought in 2019 which are still valid.