There are contemporary accounts of armies marching through head high crops of cereals and literally bumping into or at least being surprised by the enemy because they couldn't be seen through the standing crops. Think of Quatre Bras where French lancers surprised the 42nd Highlanders before they could form square because '...the stalks of rye, like reeds that grow on the margins of some swamp, opposed our advance; the tops were up to our bonnets, and we strode and groped our way through as fast as we could.' (Sergeant Anton of the 42nd Highlanders).
I think these'll do very nicely!
|The astro-turf sample|
|French voltiguer hiding in the crops|