Hello –
I wish I could give you a good answer, but it really depends on the weed killer used in the garden. Most organic herbicides work by dehydrating or burning the weed. They do not travel through the soil and are only effective when wet. Treated areas may be replanted five days after application.
Other herbicides, like Monsanto’s Roundup®, can persist in the soil for years and have been linked to Parkinson’s disease, infertility and cancers. Your best course of action would be to track down the specific product they used and check the label for recommendations.
We’ve written several articles on herbicides and how to get rid of weeds here.
https://www.planetnatural.com/category/pest-control/get-rid-of-weeds/
Hope this helps!