Only 120 allotment plots were created by councils in Wales in the last year, although more than 4,000 people are waiting.
Figures released under the Freedom of Information Act suggest councils are struggling to bring waiting lists down.
Celebrity chef Hugh Fearnley-Whittingstall said it was "madness" for councils to "sit on" land which could be made available
He wants surplus land made available, even in the short term.
In Neath Port Talbot, five allotments were allocated last year for a waiting list of 217 people. In Powys only one person of 112 waiting was given a plot.
Mr Fearnley-Whittingstall, also a food writer and campaigner, has set up a website to encourage those with surplus land to share it.
He said councils need to do more to free up space for vegetable growing.
He told BBC Wales' Politics Show programme: "A lot of councils are sitting on land the future of which is uncertain, but they may know that for at least two or three years nothing is going to happen to it," he said.
"It's madness not to make that land available, even if it's understood that it may not be forever."
The law states that local authorities must provide allotments to meet demand.
A committee of Assembly Members is investigating allotment provision in Wales.
The Politics Show found seven local authorities do not have a budget for creating and maintaining allotments.
In addition to Neath Port Talbot and Powys, they are Flintshire, Gwynedd, Carmarthenshire, Anglesey and Bridgend.
One of those on the waiting list is Allan Rees, chairman of the National Society of Allotment and Leisure Gardeners, who has been without an allotment since he moved house last year.
Fresh fruit and vegetables
"I've been on it for a year and at the moment there is a six-year waiting list so it looks as if I've got five years left to wait," he said.
"It's a nightmare, we shouldn't have to wait this length of time to be able to grow fresh fruit and vegetables for our families."
Plaid Cymru AM Leanne Wood, who can often be found tending to her allotment in the Rhondda in her spare time, is a member of the assembly's sustainability committee, which is looking into the issue of allotment provision.
"I think there's evidence to suggest that many local authorities have not responded positively to petitions from local people for allotment land," she said.
"They often look at the situation and come back and say that the land isn't available.
"What I would argue is that that situation isn't acceptable, it is up to the local authority to provide land to meet demand - demand is there they have to provide it."