Firefighters have been called to the same allotment three times in as many months.
The crew, from Bradford fire station, were called to the allotment on Harewood Street, Bradford after it was set alight again at midnight on Wednesday.
They suspect the fire, which completely destroyed the wooden building, was started deliberately.
A spokesman for West Yorkshire Fire said: "These kind of fires do spread quite quickly so it could be dangerous if somebody happened to be trapped inside one of them.
"It's a shame because they are some people's pride and joy.
"The allotments look well kept and so it must be annoying to the occupants who put time and effort into them."
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