You’re in the garden, staring at that same patch of weeds spreading year after year into your flower beds. You grumble how invasive they are. Or are they aggressive? Conversationally, both invasive and aggressive paint the same picture but if you read the fine print, they mean different things.
In everyday conversation, the two words can sound interchangeable. In horticulture and ecology, however, they mean different things. That distinction can shape how we manage plants, communicate with other gardeners and landscape professionals, and understand the regulations that apply to certain species. Gardening lingo can be nuanced and details matter.
Let’s begin with the broadest term: weed. A weed is simply a plant growing where it is not wanted. A weed may be otherwise desirable when it’s growing where we want it. Ralph Waldo Emerson famously said a weed is “a plant whose virtues have not yet been discovered.” A weed is more a description of where a plant is growing; it does not give away information about the plant’s provenance or growth habit.
Aggressive describes the growth behavior of a plant. Weeds and plants we grow in our gardens can be aggressive. Native and nonnative plants can be aggressive too. Aggressive plants can outcompete other plants for resources and outgrow the space allotted to them. Not all aggressive plants are invasive, but in some cases an aggressive, non-native plant can be categorized as invasive.
Invasive plants are nonnative and have demonstrated the ability to spread aggressively, establish outside of cultivation into natural areas, and outcompete native plants. People have introduced plants beyond their native ranges for centuries both intentionally and unintentionally. Most introduced, nonnative plants do not become invasive, but those that do can cause significant, costly problems for landowners, communities, and land managers. Invasive plants often have legal or regulatory implications.
The way invasive plants are regulated varies state to state. In Connecticut, a plant is considered invasive if it meets a set of ecological criteria outlined in Connecticut General Statutes 22a-381a. Connecticut’s Invasive Plants Council uses these criteria to recommend which plants belong on the state’s invasive plant list. The list is periodically updated by the State legislature as additional plants meeting the invasive plant criteria are identified. There are more than 100 plants on Connecticut’s invasive plant list.
What does it mean for a plant to be native or nonnative? Native plants are species that have occurred in a region without the benefit of human introduction. Depending on the context, native can mean native to the United States, to New England, to Connecticut, or to a smaller locale. There are different opinions about what makes a plant native and at what geographic scale. The most important consideration is that native plants coevolved alongside other species in their native range and are part of the greater ecological community. Native plants can be considered aggressive, but they are not considered invasive.
In summary, what defines a weed is a matter of opinion. Aggressive plants have robust growth, can be native or nonnative, and are sometimes further classified as invasive. All invasive plants are nonnative and are usually aggressive.
