I haven't had any grass stains but I've had to wash it. It IS very difficult. You can't throw it in the washer because of the clips. I think stains would be the LEAST of your worries if you tried that.
I used a large/wide bucket and hand washed it like Granny Clampett. Then I hung it out to dry.
I've thought about ordering a new one but it is quite expensive for what it is. It really needs to be a little heavier material IMO. Also, is the clips/rings were reversed so that the rings were on the screen side, it would be much safer just to throw it in the washer.