Ragweeds are weeds
that grow throughout the United States. They are most common in the Eastern
states and the Midwest. A plant lives only one season, but that plant produces
up to 1 billion pollen grains. Pollen-producing and seed-producing flowers grow
on the same plant but are separate organs. After midsummer, as nights grow
longer, ragweed flowers mature and release pollen. Warmth, humidity and breezes
after sunrise help the release. The pollen must then travel by air to another
plant to fertilize the seed for growth the coming year.
usually grow in rural areas. Near the plants, the pollen counts are highest
shortly after dawn. The amount of pollen peaks in many urban areas between 10
a.m. and 3 p.m., depending on the weather. Rain and low morning temperatures
(below 50 degrees Fahrenheit) slow pollen release. Ragweed pollen can travel
far. It has been measured in the air 400 miles out to sea and 2 miles up in the
atmosphere, but most falls out close to its source.
These annual plants are easily overgrown by turf grasses and other perennial plants that come up from established stems every year. But where the soil is disturbed by streams of water, cultivation or chemical effects such as winter salting of roads, ragweed will grow. It is often found along roadsides and river banks, in vacant lots and fields. Seeds in the soil even after many decades will grow when conditions are right.
Come late summer,
some 10 to 20 percent of Americans begin to suffer from ragweed allergy, or hay
fever. Sneezing, stuffy or runny nose, itchy eyes, nose and throat and trouble
sleeping make life miserable for these people. Some of them also must deal with
misery can begin when ragweeds release pollen into the air, and continue almost
until frost kills the plant.