I garden organically and have an invasion of nut grass in three of my gardens and a lawn area. I have dug out the soil and sifted it but a few days later it's back worse. How do I get rid of this?
Nut Sedge or Nut Grass Eradication
Certified GKH Gardening Expert
Unfortunately, the only recommended method for controlling this grass is what you are already doing.
The only other thing I would suggest is that you lay a black tarp over the area for a few months. Then when everything is dead under, you can uncover, and re-seed with the grass of your choice.
Here is an article with more information: https://www.gardeningknowhow.com/plant-problems/weeds/controlling-sedge-weeds.htm