A portable steam generator is being used on a small scale by the nursery industry to sterilize soil without chemicals. John Gray, marketing manager for the Sioux Steam Cleaner Corporation in Beresford, SD, says that the unit has been used successfully in greenhouses for more than 20 years.

"We've used this system to kill molds, fungi, nematodes, weed seeds, and other soil pathogens that attack cut flowers, bedding plants, potted plants, and vegetables. It is also excellent for sterilizing nursery tools, pots, floors, and other surfaces that can be contaminated by pathogens," Gray says. "It is an ideal technology for sterilizing soil as well as soilless growing mixes to produce disease- and insect-free plants."

Called Steam Flo, the steel generator is designed for growers who want a mobile steam source. Mounted on two15-inch wheels and equipped with a trailer hitch, it can be moved as necessary from place to place by hand or truck and can sterilize a 5-foot x 50-foot bench in about 2 hours.

Steam Flo produces steam at full operating pressure in just 15 to 20 minutes from the time it is connected to a water supply and plugged into a standard 115-volt electrical outlet. Unlike boilers, this unit will provide quick, portable steam and can be used as a supplemental steam source, so the boiler does not need to be fired up for small projects. If extra heat for short periods of time is needed, the generator can be hooked to hot water lines with a circulating pump or steam line for perimeter heat in hotbeds or plastic houses.

"There is no recovery time and the unit produces 200 pounds of steam per hour, using about 3½ gallons of fuel oil per hour," Gray explains. "And it requires only 37 square feet of floor space."

Proper water level is maintained by a low-water-sensor switch and automatic water feeder. Safety features include a steam pressure relief valve and controls for high pressure and stack pressure.

Gray says that many units built 20 years ago are still in service. The technology has been applied extensively on raised greenhouse beds and soil. Tests and market research are being conducted to determine effectiveness on ground beds and fields. In addition to increasing the efficiency of the oil firing units, the company is adding LP and natural gas units to meet growers' needs.

"Steam is a tried-and-true technology that has been used for over a century. As chemicals are increasingly becoming more regulated, experts in the field are getting more excited about the possibilities of using steam to control pathogens. It is a proven viable technology from an economic and an environmental standpoint," Gray says.

"Now that the ban on methyl bromide is only 3½ years away, we're working to improve the design of our steam generator. Although the unit is not suited to sterilize large fields of soil, we've received a lot of interest from smaller growers of cut flowers, bedding plants, and vegetables."