Exhibitors including the RHS said visitors had not been attracted to the event, billed as a "rare opportunity to visit the historic gardens of Clarence House, Lancaster House and Marlborough House, as well as to experience a unique festival in the heart of London".
Promoters said: "Think of it as the Hay-on-Wye festival, the Ideal Home Show and Grand Designs with a sprinkling of a summer festival." But exhibitors said there was more buzz at the Devon County Show.
The garden party was part of the Prince's Start initiative, launched in February to give people inspiration to live more sustainably.
Stars such as Alan Titchmarsh, Ben Elton, Jools Holland, Sir David Frost and Dame Vivienne Westwood presented music, food, gardening, comedy and fashion sections of the event. Also on the bill were Archbishop John Sentamu, Jonathan Dimbleby, Sir David Attenborough and veteran entertainer Rolf Harris.
Asda, Tesco, IBM, B&Q, Marks & Spencer, Virgin, Eurostar, EDF Energy and BT exhibited their green ideas alongside farmers' markets, gardens, bars, souvenir stalls and small eco businesses.
Exhibitors blamed poor timing, poor weather and a lack of publicity for the low attendance. But a Clarence House representative said they were pleased with ticket sales, which "met expectations".