This complex association of underground growth is what prevented the early settlers from actually using the prairie to grow their crops. They found it easier to clear forested areas to start their farms. The number of weed seed in the soil is variable and may range from 2 seeds per pound of surface soil in grassland to 140 seeds per pound of surface soil in cropland. On a per acre basis, the seed content can approach 200 million seeds per acre. Weed seed can also enter a field from outside sources such as wind, water, animals, and man.
Wind easily blows mature seeds easily from nearby plants.
Surface irrigation water and rain runoff carries many kinds of weed seed. Many weed seeds pass through the digestive tract of animals such as birds and rodents and remain viable. We have had serious weed problems with our site from the very beginning. Exotics such as lambsquarter, horseweed, and giant ragweed have been very aggressive. Several aggressive native plants, such as fleabane, hairy aster, and goldenrod, have also presented a serious challenge to the quality of the prairie.