Tilling up weeds
I changed my garden this year, a lot of grass got rototilled up, do I need to get all of the chopped up pieces out or can I leave it in for mulch?
Your title says tilling weeds and the message says grass. Left on the soil, grass roots will try to re-establish themselves. Some weeds act as though tilling were a means of propagation: each bit of root starts up a new plant. Therefore, rake up and remove what you can. Toss it into the compost pile. Watch for return of the weeds so you can pull them while still small.