This post-emergent, non-selective herbicide generally breaks down within days to weeks depending on the specific product you have. In fact, the majority of residentially sold weed killers are required by law to break down in the soil within 14 days, if not sooner. If you want to be extra sure, you can wait a week or two before planting.
This means that for the most part, it is safe to plant anything, edible or non-edible, in a place where you have sprayed weed killer after three days. This is why most weed killers are designed to evaporate within 24 to 78 hours. If weed killer was still present in the soil, you would not be able to grow anything. Many weed killers are designed to attack the plant’s root system. Chances are, the fruit or vegetable plant you are growing isn’t resistant to weed killer, or most herbicides in general. Very few plants can survive a weed killer chemical, and the ones that do are either genetically modified to do so or are weeds that have become resistant. The first thing to realize is if the weed killer was still present, chances are your plants would not be able to survive. So the questions “How long does weed killer last in the soil?” and “Is it safe to eat food grown in spots where weed killer has been sprayed previously?” can come up. These chemicals may not be something you wish to have contaminating plants, especially fruit and vegetables. Weed killer ( herbicide) can be an effective way to get rid of any unwanted plants you may have growing in your yard, but weed killer is normally made up of pretty potent chemicals.