Answer: I think the answer to your question depends upon what herbicides you used. Most of the broadleaf weed killers available to home owners biodegrade when exposed to fresh air, sunshine and moisture. Some break down faster than others. If it has been 30 days since you applied the herbicide, the soil should be safe to grow veggies - you'll know right away. If the plants keel over after being planted, the soil is suspect. If they grow well, there's probably no residue remaining in the soil. If you're still concerned, grow only above ground veggies; no carrots or potatoes or turnips during the first growing season.
Best wishes with your veggie garden!
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