Q: We had a large oak tree removed and the area underneath sprayed to control English ivy. I would like to plant a vegetable garden in that area next summer. How long does it take weed killer to dissipate?

A: Most weed killers are gone within six months. You can test whether there are any lingering effects by tilling your plot and planting radish seed in a few shallow rows. If the radishes seem to sprout normally, your vegetables should be fine.