Is A Weed an Invasive: Understanding the Differences

Every gardener can relate to seeing an undesired species growing next to a beautiful display in the garden. If a weed is growing next to a prized hydrangea, the urge to pull it is strong. As the Johnson County horticulture ornamentals and turf extension agent, I agree that some of these plants must go. However, remember that not all weeds have the same environmental impact.

When I was an amateur landscaper, I would pull plants out of flower beds that looked unappealing to me. I didn’t know much about plant identification back then, so I often pulled plants the homeowner liked. I have before-and-after photos from that period and now realize that many of the plants I thought were invasive weeds were actually aggressive cultivated or native plants. Intentionally placed there, then allowed to spread uncontrolled.
As a society, we think of any plant we don’t want, or not in the right location as a weed. Many gardeners also refer to them as invasive weeds. The USDA defines invasive weeds as “non-native to the ecosystem under consideration and whose introduction causes or is likely to cause economic or environmental harm or harm to human health.”

Environmental, economic, and human health impacts vary by region and seasonal weather patterns. The economic impact can come from decreased yields from competition for resources with weeds, by killing livestock or from reduced property values. Human health may be impacted by the plant’s physical traits, such as thorns and chemical properties, or other plant byproducts, such as pollen.

“Non-native” also has many different colloquial meanings. Generally, when we use the term “non-native,” we refer to a plant not native to the U.S. However, we should also use it to describe plants not native to a specific ecosystem.
For example, eastern red cedar is native to the eastern regions of the United States. However, in grassland ecosystems, it is invasive and negatively affects the diversity of vegetation that grows there. Not only does it shade out the beneficial native grasses and forbs underneath the canopy, but the female trees produce an abundance of viable seeds that hungry birds disperse and spread farther. Without consistent control measures taken by humans, the eastern red cedar soon claims grassland.

The invasive weeds we are familiar with in landscaping can grow in a wide range of environmental conditions, and often appear when a site is recently disturbed. Purple deadnettle, crabgrass, henbit, bindweed, and dandelions are all examples of invasive plants from a different hemisphere. Not only do they take space, nutrients, and water away from native vegetation, but they also grow in almost every kind of condition imaginable.

You can find these invasive weeds thriving in manicured beds filled with ornamentals, cracks in the sidewalks and roads, or on top of a bed of rocks. Fast-growing, combined with prolific seeds, their tenacity is the key to their success.

One could argue that a plant considered invasive isn’t necessarily evil. Much of our wildlife has adapted to take advantage of what they produce. From one early source of pollen for bumblebees (dandelions) to one of the host plants for hummingbird clearwing moths and snowberry clearwing moths (bush honeysuckle.)

Invasive honeysuckle is also objectively destroying the understory layer of our oak and hickory forests, shading the forest floor and releasing a growth-inhibiting chemical in their leaves and berries. Still, the berries have become a food source for birds. The birds inadvertently continue the spread cycle by taking advantage of the berry bounty.

The point is that invasive plants are well adapted to survive in the new areas in which we find them. They lack natural checks and balances, contributing to their success story.

These ‘invader’ plants didn’t choose to be there and didn’t carry malicious intent when growing and competing with other plant life. They are doing what all plants do: grow and try to pass on their genetics to the next generation. To keep them from becoming invasive, and considered weeds, humans need to be intentional about keeping numbers in check.

by Markis Hill, Horticulture Ornamentals and Turf Agent, 2025