Spring, summer, and fall are all allergy season for some unfortunate people who are allergic to pollen. In spring, it’s early-flowering, wind-pollinated trees. They release large amounts of pollen in hopes that a few grains will find their way to a waiting flower. Because they don’t need to attract insects, they are small and inconspicuous. In summer, the grasses take over — and people can be allergic to both grass and trees. In fall, it’s the weeds such as ragweed. Perhaps due to global warming, the ragweed season has lengthened by almost a month in Canada.
You can read about pollen allergies here.