A.: For many years the beautiful goldenrod (genus Solidago) that blooms in late summer and fall has taken the blame for the bad habits of common ragweed, which blooms at the same time. The goldenrod is much more flamboyant than ragweed, so it is the one people notice when they are suffering. However, goldenrod pollen is heavy and unlikely to become airborne to be inhaled and trigger an allergic reaction. It is possible to be allergic to goldenrod, but much less likely than being allergic to ragweed. Ragweed pollen is light and depends on the wind to transfer it from flower to flower, so it is more likely to be inhaled by humans. It is a common, if not the most common, cause of hay fever in the fall.
Goldenrod is a perennial plant that grows to a height of 2 to 5 feet. The leaves are numerous, narrow and lance-shaped with prominent veins and jagged margins. The multi-branched flower heads form at the tops of the stems. They are bright yellow and bloom in long spikes that droop gracefully. Goldenrods provide pollen and nectar for bees and other beneficial insects, so it is better to let it grow where possible. It is an attractive, low maintenance wildflower which is a welcome addition to the late-summer and fall garden. If you do not want it in the garden, it can be controlled by hoeing and digging. It may be necessary to do this several times. A dense layer of mulch will help to prevent new plants from sprouting and smother new shoots.
Ragweed (Ambrosia artemisiifolia) is common in the eastern and north-central United States. It is a nondescript, annual weed that grows to a height of 1 to 3 feet. The green, hairy stems are straight and may branch near the top. The leaves are smooth and deeply lobed, almost fern like. It blooms from July through September. The flowers are 2 to 4 inch long, greenish spikes that grow from the tips of branches. Male and female flowers are located on the same plant. The male flowers are at the top of the plant and usually droop. The female flowers are located at the bases of upper leaves. One ragweed plant is estimated to produce 1 billion particles of pollen. Seeds scatter from a brown-woody husk with spines to produce plants for the next year. For pictures of ragweed in various stages of development see: http://www.ppws.vt.edu/scott/weed_id/ambel.htm.
Seventeen different species of ragweed are found in North America. It grows best in full sun and newly worked soil that is free of other weeds. It is often found along roadsides, in vacant lots, abandoned fields and river banks.
In most places ragweed is considered a noxious weed and is governed by weed control ordinances. It is a shallow-rooted plant that is controlled by hoeing and pulling. Heavy mulch helps prevent seeds from germinating. Mowing roadsides and patches of weeds near your home prevents ragweed from blooming, therefore prevents the production of seeds and the next generation of plants.