Answer: Yes you can. Check the Roundup label. It usually will state how long to wait after treatment before replanting. I would suggest you give the Roundup 7 days to work before mowing or rototilling the area. After mixing the dead weeds with the soil, wait another 7 to 10 days for the herbicide to tie up in the soil and break down into harmless materials. This should give more than enough time to remove any risk to the seeds and transplants you set out.
Once again, check the label. It is the final authority.
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