Crews responded to Growers Choice Hydroponics at 16754 E. 14th St. in San Leandro just after 2 a.m., spokeswoman Aisha Knowles said.
They arrived to find smoke and flames but managed to extinguish the fire by about 2:20 a.m., Knowles said.
A fire battalion chief estimated that about 25 percent of the business sustained some smoke or fire damage, and said the roof will need to be repaired.
Knowles said the blaze caused about $100,000 in damage to the building and $200,000 in damage to its contents.
No one was in the building at the time of the fire and there were no injuries, she said.
After the first crews arrived at the scene, the one-alarm fire was upgraded to a second alarm, Knowles said. However, when the second unit responded, the second alarm was canceled, she said.
The cause of the fire has not yet been determined, Knowles said.
