After Kevin Tran escaped from Crowley, Crowley sent several demons to guard Linda Tran knowing Kevin would return to check on his mother.
After Kevin reunited with Sam and Dean Winchester they went to Linda's house to see if she was safe. After staking out the house for some time Sam and Dean realized the gardener was a demon due to his excessive watering of Linda's house.
The gardener is watering plants with a hose when all of a sudden the water stops flowing and he walks around the side of the house to investigate. Dean sneaks up on him and stabs him with the Demon-Killing Knife. The gardener screams and falls down dead.