In the spring, trees are the primary source of airborne pollen. During the summer, grasses take the lead role, followed in the late summer and fall by weed pollen, including the dreaded ragweed.
The following five plants are among the worst offenders when it comes to spring allergies. Why? Because they rely on wind, not on insects, to disperse pollen. As a result, they produce a lot of it to increase the chances that grains will reach and fertilize a female flower.
Of course, all that airborne pollen also means more of it is likely to reach your nose and eyes. Read "10 Tips to Reduce Your Exposure" for ways to manage spring allergies.