I've had engines last a very long time that have sucked some grass into them.
While I don't abuse my engines, I don't pamper then either...or run aircleaners on them unless they're in a car. Grass and dirt are part of our flying fields...they're not going anywhere anytime soon. And on take off and landings in fresh cut grass chances are you're going to suck a little in.

I would be more concerned with lean runs and rust prevention...two things far more detrimental than a little grass