Place the jars in a warm, sunny location. Lettuce seeds usually germinate in 2 to 3 days under these conditions. Compare the germination of seeds placed in treated and untreated soil. Reduced or delayed germination of the seed in the treated soil sample jar indicates that chemical residues are still in the soil and it is unsafe for planting. Repeat the procedure at 5 to 7 day intervals until the bioassay indicates it is safe to plant.
Aerated steam is an alternative soil fumigant.
It is very safe, but requires a steam generator, an aerator, a steam injecting system such as canvas tubes, and a tarp for covering the bed during steaming. Aerated steam is not used much in the landscape, but steam may be used more in the future as we lose soil fumigants. Suggested spacing for bedding plants in the landscape. Planting too deep can increase disease problems, and planting too shallow results in weak, poorly anchored plants. Plant in soil, do not plant in mulch.