Disclaimer: its been a while...
Grass itself does not really make a strong sound unless it's dried up grass.
So unless you have close ups of feet walking in grass spend less time to recreate the grassy part of the sound. The green grass sound is mostly about a good NON resonant soil sound, with a little grassiness on top.
Old school was using old quarter inch tape, the scrappier the better (if it's to new it will crackle to much). Place a thin rug or towel over it in the dirt/soil pit and go from there. Quarter inch tape can be replaced with other materials, paper based stuff has a very limited lifespan. Plastic can easily sound to plastic.
IMHO less is more in terms of green grass rustle. But then the less there is, the more it will stand out when it's there. Careful editing and de-essing can also help to get the sound feel right.