Most weed killers are designed to evaporate within 2-3 days. So it’s safe to plant in your garden 4-5 days after spraying weed killer. If you want to be extra cautious, you should wait 1-2 weeks. That said, the glyphosate contained in weed killer will harm and probably destroy your plants if direct contact is made with any part of the plant. So you should avoid spraying herbicide within 1-2 feet of your plants, especially because the soil soaks up and spreads the toxins in weed killer. For an organic alternative, you could try mixing together the following ingredients: vineager, salt and dish soap. This natural approach can be an effective tool against weed growth, though not as reliable as store bought weed killer concentrate.