Shane Fuller was delivering milk about 4.40am (AEST) on Wednesday at Spring Hill when he saw a planter box on fire on the footpath.
"The flames were about half-a-metre high - some of the mulch and palms were starting to burn," he told ABC Radio.
"I just jumped in and made sure it couldn't get any worse.
"I didn't have any water so I just grabbed some bottles of milk and just drenched it."
"Normally I use water, but it had to be milk today, that's all I had."