What can you use to kill yard grass so you can till up?

To kill yard grass before tilling, you can use a non-selective herbicide containing glyphosate, which effectively kills all vegetation. Alternatively, you can use a natural method by covering the area with black plastic or cardboard for several weeks to block sunlight and decompose the grass. Another option is to apply a thick layer of mulch or newspaper, which will also smother the grass over time. After the grass is dead, you can safely till the area.