noun: to blow a big wad of snot out of one nostril while holding the other nostril closed by pressing on the side of the nose with the index finger or thumb.
When done properly, a farmer blow completely clears the nasal passage and the small amount of snot remaining on your nose can be wiped off on the back of your glove or on your sleeve. Good if you do things outdoors a lot and don't want the mess on a handkerchief in your pocket.
Block one nostril and exhale forcefully through the other to expel a large deposit of snot.
Done when no handkercheif or tissue paper is handy.
I could feel the snot in my nose, but I didn't have a handkerchief handy, so I had to farmer blow.
A blow job from a farmer.
"You spent the whole summer on a dude ranch?! That really sucks"
"It could have been worse, at least I got a farmer blow"