Two crews from the city turned out to battle the blaze at Booth Field allotment, between Castlecroft and Compton, at 2.38am this morning.
A shed was destroyed and completely engulfed by the flames on the Compton Road West site.
A spokesman for the service said: "We received a 999 call at 2.38am this morning to Booth Field allotments on Compton Road West.
"We sent two crews to the scene, a fire engine and a brigade response vehicle.
"An allotment shed has been 100 per cent destroyed by the fire. We used a hose reel jet to put the blaze out."
The fire is believed to have been started accidentally, the service added.
