A National Allotment Society poll found that 74 per cent of its members were concerned for the future of their plots, said national secretary Donna McDaid, who is urging more people to become involved in the week on 6-12 August.
"Since the Localism Act came into force, there is an even greater need to galvanise the interest and support of local communities, especially as planners see allotments as prime development land," she said.
Artist Chris Cyprus's painting Open Day will be reproduced on allotment gates across the country in the lead up to National Allotments Week. Some 35 events are planned, from barbecues and plant stalls to cream teas and festivals.
Meanwhile, English Cities Fund's Vermilion mixed-use development at Rathbone Market in Canning Town, east London, includes 30 private allotment plots for rent at £150 a year.