Roundup and planting
If Roundup was used (twice) in a patch of soil, will mixing the soil with lots of purchased garden soil allow you to grow plants there? Or how long will you have to wait before planting flowers there? Regular Roundup.
Certified GKH Gardening Expert
Almost all weed killers have a period of time after which it is safe to grow plants. The time varies but usually takes about a year for anything edible and less for flowering plants. Here is more info: https://www.gardeningknowhow.com/garden-how-to/soil-fertilizers/how-long-does-weed-killer-last-in-the-soil.htm