The Great Plant Sell-Off happens on the final day of Chelsea Flower Show, when polite chaos ensues as the public pick up a bargain in this quintessentially English of pastimes, which also marks the end of Spring and the start of Summer.   A group of people sit a cafe in Sloane Square, Chelsea after The Great Plant Sell-Of, which happens on the final day of Chelsea Flower Show, when members of the public get a chance to pick up a bargain in this quintessentially English of pastimes, which also marks the end of Spring and the start of Summer. 28 May 2022.