Q: For several years I developed terraced vegetable beds on a slope and they produced prolifically with no significant problems. Last winter, I added another bed and filled it with “garden soil” from a local landscaping supply company. This summer that bed is doing terribly. Could the topsoil have come from a pasture contaminated with herbicide?

A: I’ve had great results with soil from professional landscape supply companies. I’d ask your source about their suppliers. But if you suspect herbicide damage, the simplest answer is to do a bio-assay. Mix the soil 1:1 with potting soil and plant a small tomato in it. Tomatoes are very sensitive to herbicides and will let you know within a week if the soil is contaminated. More details at xrl.us/bioassay.