The fire is on Texas 242. Twenty fire trucks are on location, and firefighters on scene are calling for more help from Cleveland.
Officials said the flames are contained to the processed mulch and have not spread to the surrounding woods.
According to the owner, the pile consists of 22,000 yards of mulch.
The fire appears to have began in the green area of the mulch yard. The business was closed for the day when the blaze started.
The owner said it could have been a discarded cigarette in the green pile that ignited the fire.
When firefighters arrived, flames were shooting off the top of the unprocessed pile.
As firefighters flow more than 1,000 gallons per minute of water over the pile, large machinery is taking the pile apart one scoop at a time.
The fire is expected to burn throughout the night.
Two firefighters were treated for heat-related injuries during Saturday afternoon's triple-digit temperatures.
Please stay with Eyewitness News and abc13.com as we continue to gather new information on this developing story.