Most trees release their pollen in the late winter and early spring.  In the Southeastern U.S., tree pollen season can begin as early as January.  Contrary to popular belief, it is typically not the trees with large, colorful flowers that cause allergy, but more often those trees with smaller more inconspicuous flowers.  Some of these allergy-causing trees include:

Ash, Aspen, Beech, Birch, Box Elder and other maples, Cedar, Cottonwood, Elm, Mulberry, Oak, and Willow.

Most grasses release their pollen in the late spring and early summer. Grasses tend to release more pollen when they grow.  An exception to this is Bermuda grass, which will release pollen even when kept very short.  Grasses most likely to cause allergy symptoms include:

Bermuda, Johnson, Kentucky Bluegrass, Orchard, Redtop, Rye, Sweet Vernal, and Timothy.

Most weeds release their pollen in the late summer and fall.  Although ragweed pollen is the most well-known culprit for causing allergy and asthma symptoms, there are other allergy-provoking weeds.  These include:

Burning Bush (also known as kochia, Mexican fireweed, summer cypress), Cocklebur, Lamb’s Quarter, Pigweed, Plantain, Red (sheep) Sorrel, Russian Thistle, Sagebrush, Mugwort, Scales (atriplex), and Tumbleweeds.