Papers in the Biological Sciences


Date of this Version



Published in ENCYCLOPEDIA OF THE GREAT PLAINS, ed. David Wishart (University of Nebraska Press, 2004), pp. 641-642. Copyright 2004 University of Nebraska Press. Used by permission.


According to the U.S. Department of Agriculture, countless hours and millions of dollars are spent each year to control weeds, and millions more--hours and dollars--are lost in yield reductions. However, what exactly is a weed? And what makes a plant a weed? Many people are surprised to learn that a weed is technically "a plant out of place." So one person's weed can be someone else's salad green, pharmaceutical, transgenic crop, or wildflower!

What are the characteristics of plants that often grow out of place? One characteristic is a tendency to reach high numbers rapidly and to replace or slow the growth of more desirable plants. Traits allowing rapid population growth include early development, fast reproduction, and many long-lived seeds. Structures that aid dispersal often help weedy plants colonize far and wide. Finally, many weeds lack effective enemies, such as insects and diseases that reduce plant growth and reproduction.