Firefighters were called to a Kings Langley farm after a large pile of logs caught alight.
Crews from Hemel Hempstead and Kings Langley went to Gade Valley Close just before 3.30pm yesterday.
They used hose jets to battle the flames and ensure the fire was under control before leaving the scene.
Firefighters have been returning to the farm every few hours throughout the night. They will continue to visit today until the blaze has burned itself out.
The cause of the fire has been recorded as accidental.