Time to put the mower on the tractor. I have a 1957 Ford 640 tractor and a five-foot rotary mower.
The surest sign that it’s time to mow is that the electric fence starts shorting out against it. You’ve really gone too far when the chickens have little jungle paths through the tall grass to get from their houses to the outdoor feeders.
Chickens do best on short grass. They can’t digest grass unless it’s bright green, and tall grass is a serious barrier to them. I read some research done way back when that said that two inches is a good grass height for chickens. Six inches is too tall. Also, when tall grass starts providing seclusion, they start laying there instead of in the nest boxes.