Four fire engines and around 25 firefighters were called to reports of sheds alight on Long Elmes in Harrow.
Five garden sheds and around 50 square metres of garden shrubbery were destroyed by fire. Firefighters cooled a gas cylinder and cooled to an ambient temperature as some cylinders can explode when exposed to heat. There were no reports of any injuries.
The Brigade's 999 Control Officers took 22 calls to the blaze.
The Brigade's Fire Investigators believe the fire was caused by the unsafe use of a fire pit.
A London Fire Brigade spokesperson said: "If you use fire pits in your garden, make sure you place it completely clear of anything that could catch fire, like garden sheds, garages and fences.
"Damp down burnt materials with plenty of water."
The Brigade was called at 2002 and the fire was under control by 2136. Fire crews from Harrow, Stanmore and Northolt fire stations attended the scene.