Q: What would happen if I let my emerald zoysia grass grow on a steep bank
without mowing? 

A: It will be “tufty” but could be somewhat attractive. Plant three-inch
diameter plugs of grass six inches apart in May. Try to control water flowing
down the bank to avoid erosion around the plugs. Fertilize lightly. You should
use a string trimmer to mow it once a year in late spring.