I have literally seen in person the claim that grass tall enough for seedheads exacerbates grass pollen allergies. This was in a small town surrounded by farmland with some of the most fertile soil in the world. A person with grass pollen allergies would have to be a fool of the highest caliber to blame them on a neighbor's unmowed lawn rather than the wind blowing in from the sod farm, or the hay farm, or the wheat farm. Sometimes, I had to mow twice a week to keep the grass at a reasonable height. If I had a grass pollen allergy, I think maybe I could have been better off moving to Phoenix than becoming a lawn-height snitch--or as a UK person might put it, a grass grass.