The Chelsea Flower Show will take place in September for the first time in its history as a result of the pandemic.
Organisers had planned to hold a six-day show in May but announced it would be postponed as there was no guarantee what tier London would be in then.
A virtual show will take place in May like in 2020, with the physical event taking place later at London's Royal Hospital Chelsea.
The Royal Horticultural Society (RHS) said it would be a "moment in history".
The world-famous show has been taking place for 108 years but has never happened in September.
This year's event will go ahead between 21-26 September, with the virtual event showing online from 18-23 May.
It is usually filled with spring and summer colours but the RHS said it hoped the delay will allow a celebration of autumn horticulture.
The society, which runs the event, said it had a responsibility to exhibitors, visitors, volunteers and staff to delay the flower show, as more people would be vaccinated and levels of infection may have reduced substantially.
Director general Sue Biggs said: "Whilst we are sad to have had to delay RHS Chelsea and are sorry for the disruption this will cause, we are excited that we are still planning to bring the world's best-loved gardening event to the nation at a time when more people are gardening more than ever.
"We know that the autumn dates may not be suitable for everyone, but with our fantastic industry partners we will do everything we can to support them and create a show that will be a moment in history," she added.
Those who bought tickets for the event when it was due to happen in May will be contacted by the RHS.
Chelsea Flower Show
- The first show opened on 20 May 1913 with the first events held over three days within a single marquee
- A show still took place in 1915 after war was declared in Europe. although with fewer exhibitors. It was then cancelled for the duration of World War One
- Rain during the 1932 show was so severe that a summer house fell to pieces
- The flower show was discontinued again in 1939 due to World War Two, only returning in 1947. A virtual event took place in 2020 due to the pandemic
- The current Great Pavilion is about 11,775 sq m (2.9 acres) in size, approximately enough room to park 500 London buses