What’s a weed? A simple question has a pretty complex answer

Gardeners have many names for weeds being the bane of their existence. Weeds are lumped into categories based on how and where they grow.

What is a weed?

The definition of a weed is a plant out of place. Defining them this way means any plant could potentially be a weed. A volunteer tomato plant sprouting up in the carrot patch could be a weed if it is not wanted. Cleome reseeding in the flower garden is a weed if not controlled. If you value the plant, then it is not a weed.

A weed is a plant freely growing and out-competing desirable plants. Weeds tend to grow no matter the conditions and frequently overtake our attempts to eradicate.

Noxious verses obnoxious

Weeds are obnoxious, but this word causes confusion. Noxious weeds are a classification for extremely aggressive weeds and are placed in this category by governmental regulations. In Kansas, weeds are classified as noxious by the Kansas Department of Agriculture.

Few weeds make this list. Noxious weeds must be difficult to control and have an agronomic impact. Their presence significantly reduces crop yields and the value of the crop, whether a wheat field or pasture. Because of this, each state has noxious weed laws.

Kansas noxious weeds impacting suburbanites are Johnsongrass, bindweed, and musk thistle. Kudzu is placed in this category because of its potential damage, not because it is established in our area. Removal of noxious weeds can be enforced legally, or the landowner can be charged for their removal.

Plants can also be quarantined by states. In Kansas, the sale of purple loosestrife, also known as Lythrum, is banned due to its potential to clog waterways. The classification does not require uprooting, but a diligent person would consider removal the right move to prevent it from propagating.

Invasive

The term invasive plant is used to describe weeds, but invasive is not a regulated classification. Instead, it is a term to alert people of its potential detriment. Gardeners often think of invasive plants as those that have escaped cultivation, taking over native areas.

An example of an invasive plant impacting natural areas is honeysuckle spreading through the understory of wooded areas, choking out the native forest floor. Birds spread the seeds of Callery pear, or Bradford pear, planted in the landscape. You can find it forming thickets in our grassy areas, killing the native vegetation. Removal or not planting invasive plants is a conscious decision not enforceable by law.

Garden thugs

Some weeds are neither noxious or invasive. They’re unruly plants that spread uncontrollably and are not easily eradicated. Examples of these garden thugs are Houttuynia (chameleon plant), mint or gooseneck loosestrife. Gardeners plant them not knowing their intrusive habits. The best remedy for garden thugs is avoidance. Aggressively spreading plants may sound good, but trust me, they do more harm than good.

Fighting weeds is one of the top issues for garden success. Classifying them helps bring control to the chaos, giving us the upper hand in the battle.

Dennis Patton is a horticulture agent with Kansas State University Research and Extension. Got a question for him or other university extension experts? Email them to garden.help@jocogov.org.

This story was originally published December 19, 2019 at 8:57 PM.