Grass keeps growing in my flowerbed. I have tilled. I have pulled out by the roots. Keeps coming back.
Keeping Grass From Growing in Flowerbed
Certified GKH Gardening Expert
This can be quite frustrating to gardeners.
Tilling can actually make the problem worse, by spreading the invasive roots everywhere.
Keeping them pulled up will help the spread.
Here is a link with some more possible treatment for your area.