Species in the knotweed complex grow very quickly, causing large infestations on roadsides like this one. / Photo Credit: Randy Westbrooks, Invasive Plant Control, Inc., Bugwood.org
By Erika Segerson-Mueller, DNR Invasive Plant Program Specialist, Oshkosh Service Center;
Erika.SegersonMueller@wisconsin.gov or 715-492-0391
As you work on your New Year’s resolutions this year, you might want to add “don’t plant invasive species” to your list. Too wide-ranging? Try narrowing the goal to a species-specific suggestion: “Just say ‘no’ to knotweeds.”
Sometimes referred to as “the knotweed complex,” Wisconsin has three regulated species of knotweed: Japanese knotweed, giant knotweed and a hybridization known as Bohemian knotweed. Each has been found in the state.
Thirty years of data was reviewed by a group of horticultural, botanical and climatological experts for the latest USDA Plant Hardiness Zone Map revision. This was determined to be the best balance between the fluctuations of year-to-year weather variation and the concept that, during their lifetimes, perennial plants mostly experience what is termed “weather” rather than “climate.” A complex algorithm was used for this edition of the Plant Hardiness Zone Map to enable more accurate interpolation between weather reporting stations. This method accounts for factors such as elevation change and proximity to bodies of water, making mapping zones more accurate. 
