Aerated steam and steam are commonly used for treating soil in the glasshouse, nursery, and mushroom industries to control soil-borne plant pathogens. In treating soil in containers there is an important and disturbing tendency for the soil next to the container sides to attain the desired temperature more rapidly than does that in the central mass. This “edge effect” cannot be eliminated, but can be diminished by: a)

treating soil in layers not more than 30 cm thick;

using large flow rates of aerated steam or steam, preferably injected through a plenum at the top;

treating soil in beds by the Thomas or surface method or by buried perforated pipes or tiles, treating soil in flats or pots by a vault steamer, and treating bulk soil by a perforated-pipe steam box or a transit-type concrete mixer;

inserting vertical partitions or open pipes in the central mass if a plenum-type steam box or a mobile bin and potting table is used;

using very porous soil mixtures. Temperature measurements should be made in soil at the bottom center when steam is injected through a top plenum, and at the top center when steam injection is through a bottom plenum.