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Washington State University
WSU Puyallup Research

How the Process Works

sensorsTemperature sensors attached to dataloggers are buried in the soil at 5, 15, and 30 cm depths. There is one set of sensors for every 100 sqft of steamed area. Dataloggers are set to record the soil temperature once every 15 minutes. Soil moisture levels are monitored outside the steamed area.


A steam sock is overlaid on the plot in a spiral pattern. This conveys the steam to the plot and behaves as a “soaker hose”, allowing even distribution of steam. After installation of sensors and hose placement, the plot is covered with a reinforced PVC tarp and the edges weighted with sandbags to prevent steam escape.


The steam sock is connected to the output hose on the steam generator and steaming can begin. The length of time needed for steaming is determined by the size of the steam generator, soil moisture, and soil physical properties such as compaction and particle size.


During the steaming process, the dataloggers are monitored. When all locations have reached the target temperature of 50°C for 30 minutes, the steaming is complete.

Steam treatment to sanitize soils, pots, and media