The question was raised as to how long one should wait before
planting vegetables in soil that had been treated with herbicides.
The problem is that unless one knows the identity of the
herbicide there is no real way to answer the question. Roundup
is the most commonly used herbicide in the U.S. and that material
bio-degrades fairly rapidly. The material and the break-down products
are also fairly low in acute toxicity so it would probably be O.K.
to plant vegetables in soil that had been treated with Roundup
within a few days or a few weeks following application.
There are, however, other materials that are used as herbicides that
may not be so user friendly. What about growing your vegetables in a
raised bed filled with soil known to be clean?