Am not being flippant here. But.... local. Local pollen. Goes to reason that local pollen contains local 'things' that would have a more direct impact on one's body, than pollen from a distance place.
Learned years ago and have seen it work (I don't have allergies but from talking with people who do this), where people clear up allergies in the blink of an eye by ingesting local pollen. This really seems to have merit.
I think I wrote about this previously on here, or maybe I talked about it in my lectures. Anyway it does not really matter if the pollen is local because pollen does not really work through desensitization. It works because pollen is the highest herbal source of pantothenic acid, which is the second most important nutrient, next to vitamin C, for proper adrenal function. Healthy adrenals counter allergies. This is why pollen can help alleviate non-pollen related allergies as well.