(North Dakota, South Dakota, Nebraska, Kansas)

In this region, trees pollinate from March to May, including the oak and cedar. Other allergy-causing trees include the alder, birch, maple/box elder and hazelnut.

Grasses pollinate from late May to July in this region, including quack grass/wheat grass, redtop, brome, orchard grass and rye grass.

Weeds take over from July through September, including ragweed, plantain and nettle. Other allergy-causing weeds include the water hemp, pigweed, lamb's-quarter, Mexican fire bush and Russian thistle.