Resistance Gardening Tip: Get Rid of Invasive Species!
What's an Invasive Plant? And What is just Aggressive?
We bought our current home in the winter, and we only saw it in the snow until we closed on the house. Had I known what I know now, maybe we wouldn't have purchased it. What looked like a pretty standard lawn in front and back was, in fact, nothing but invasive weeds. And much of my work over the last eight years has been about taming, killing, and eliminating these invasive weeds. And I am not done.
Invasive plants – whether we define them as weeds or not – are a hazard. They are problems for farmers. They are problems for our ecosystems. They are one of the primary reasons people use herbicides.
But they are also often for sale.
You'll find them online, in big box stores, in garden centers, and at plant swaps. Because they aren't all "weeds." And many people don't know about or care about the harmful effects these plants have on our ecosystems.
Our Resistance Gardening Tip of the Week is to KNOW your invasive species,
get rid of them responsibly, and to teach others about them, too.
But we also need to talk about precision in language. Many people use the words "invasive" and "aggressive" interchangeably. They DO NOT mean the same thing in the plant world. Invasive plants may be aggressive – but not all aggressive plants are invasive. Some are even natives.
So our second tip this week:
we must also learn the difference between invasive and aggressive plants,
and we must use those words accurately.
It sounds like a lot, but it actually isn't so bad.
OK. Let's get started!
What Are Invasive Plants?
On social media I often see gardening influencers say, "Such and such plant is really invasive in my garden." This makes my skin crawl. This is a classic case of confusing the words "invasive" with "aggressive" – and that lack of precision can be problematic. So let's start with the LEGAL definitions – because this is actually something codified in law.
In the United States:
“An "invasive species" is defined as a species that is
Non-native (or alien) to the ecosystem under consideration; and,
Whose introduction causes or is likely to cause economic or environmental harm or harm to human health.” (Executive Order 13112).
This definition is, by the way, applied to plants, animals, fungi, even viruses! Japanese Beetles and Field Bindweed are held to the same standards. Both are jerks in my book.
So an invasive plant must have several traits to be considered invasive by law:
It is not native to North America or to the area under consideration.
This means that North American plants can be considered invasive in Hawaii and the US Territories, for example (and vice versa). Afterall, plants don't have nationalities.
Because of the vast ecological diversity in the USA, a species may be considered invasive in one part of the country that is not in another.
It is likely to cause harm which is defined in three ways:
Economic harm: to farmers, for example, but that could also be to tourism or other ecological-dependent industries.
Environmental harm: a species might crowd out native species, for example
Harm to human health: a species may be toxic or cause extreme allergic reactions, for example
These are broad definitions by design so that when the justification can be made to declare a species invasive, that justification must be made using these criteria (and others) as defined by law.
Let's also talk about Noxious Weeds.
This is a different classification. Many, but not all, noxious weeds are invasive species. But some are not – they just have populations which are not in check anymore because of environmental changes.
“Legally, a noxious weed is any plant designated by a Federal, State or county government as injurious to public health, agriculture, recreation, wildlife or property. (Sheley, Petroff, and Borman,1999) A noxious weed is also commonly defined as a plant that grows out of place and is ‘competitive, persistent, and pernicious.’” (James, et al, 19911
Why do these legal definitions matter? Well, in some states, for example, if you have a property infested with an invasive species or a noxious weed – like field bindweed – you may be eligible for help in getting rid of those plants, because they are a threat to not only your property, but to the environment as a whole.
Invasive plant examples that are also Noxious Weeds in most states:
Field Bindweed
Canadian Thistle
Japanese Knotweed
Yellow Flag Iris
Leafy Spurge
Kudzu
Lists vary state to state – more on that in a moment. But there is also a range of plants that are considered noxious across most of North America.
What Are Aggressive Plants?
What many gardening influencers actually are talking about when they say a plant is "invasive" is that some plants can be aggressive.
Take common mint, for example. The conventional wisdom is to NEVER plant mint in the ground, because you'll never get rid of it. And I will tell you: that is true. One of the non-invasive, but very aggressive plants in my yard is mint. I've kept it confined largely to one area of the garden, but it comes back every year without fail. And this spring I found it in the Orchard – a place that has never had mint before. Probably the work of a mouse or squirrel or the wind. Who knows! But now I am fighting it back on two fronts.
Mint is aggressive. It does not appear on lists of invasive or noxious plants. It may be a problem in my garden, but it has not proven to escape cultivation and become a widespread problem beyond home gardens. So it is merely aggressive.
The wisdom holds: only ever plant mint in a pot!
In general, aggressive plants:
Spread quickly
Can quickly overtake other species in a planting scheme
Can be difficult to eradicate
Do not cause ecological harm
One way to think of it: an aggressive plant will cause havoc in your yard; an invasive plant will cause havoc in your neighborhood.
And what may be an aggressive plant in one part of the continent, may be held in check by environmental conditions in another. Black Eyed Susans, for example, can become very dominant in gardens in warmer climates, but the lack of rain and our colder winters keep them under control here in Colorado.
Examples of aggressive plants in gardens:
Lamb's Ear
Dill
Snow on the Mountain
Ostrich Ferns
Lily of the Valley
Daylilies
Invasive vs. Aggressive: Key Differences
The key differences between invasive, noxious, and aggressive plants comes down to a few characteristics:
Native status within the environment
Environmental impact on the surrounding community
Legal designations: how has the state or community designates that plant
Management difficulty
This is why lists can vary from state to state. Colder winters may keep some plants in check in one part of the country that can be hugely problematic in other places. The same can be said of moisture levels, altitude, summer heat, etc.
However, that also means that as growing has become an interstate business, gardeners must be more informed.
Why Gardeners Should Care
As gardeners we are connected to the earth. We love the feel of soil between our fingers. We linger in the waning light – soaking in those last few minutes of sun and plants before disappearing into the house at night. And we want to do what is right for the land. It's part of our environmental stewardship. It's part of supporting biodiversity. It's the right thing to do.
That means avoiding invasive species – and eradicating any we may already have on our properties.
When we bought our home, my first responsibility – when the weedy "lawn" greened up – was to identify what plants we were hosting on our land. The list wasn't all that long, but it included a LOT of invasive species:
Field Bindweed (Convolvulus arvensis)
Prostrate Knotweed (Polygonum aviculare)
Canadian Thistle (Cirsium arvense)
Cotton Thistle (Onopordum acanthium)
Dandelions (Taraxacum officinale)
Siberian Elm (Ulmus pumila)
Prickly Lettuce (Lactuca serriola)
Not only are these weeds inconvenient for me, but I watch them become a bigger and bigger problem in our environment.
For example, I drive a cloverleaf to get onto the local highway nearly every day. Inside the cloverleaf is a Prairie Dog town. Prairie Dogs are a keystone species in our environment and are protected. They eat forbs and grasses – broadleaf plants native to our part of the world. In this open cloverleaf, those plants have been overtaken by one plant: Field Bindweed. I've watched it happen over the last few summers. And Prairie Dogs don't eat Field Bindweed.
So what are they eating? I don't know, but I don't see as many Prairie Dogs on my morning drive as I used to.
Now, that Bindweed has been flourishing in our area for decades, I am sure. But if I let it dominate and flower in my yard, those seeds (which are microscopic and airborne) may land in another Prairie Dog town, germinate, and crowd out the native plants upon which those Prairie Dogs depend.
When I told my neighbor, who liked the Bindweed flowers in her yard, about what I was seeing, she was rather incredulous. "One plant can do all of that?" she said. But it's true. One plant CAN do all of that. In fact, Bindweed is the primary weed problem for many farmers. I have watched it overtake roadside plantings in the few years we have lived here. And there are many yards in my neighborhood with severe infestations. How can I tell? They are blooming in late spring and early summer – and I cringe as I drive past.
And that's just one noxious weed.
So, what can we do as gardeners?
While Field Bindweed is an easy example to make, there are other more complicated situations. For example, big box stores and other garden centers often sell invasive species. A 2021 study by ecologists at the University of Massachusetts Amherst showed "that 1,330 nurseries, garden centers and online retailers are still offering hundreds of invasive plant species as ornamental garden plants. This includes 20 species that are illegal to grow or sell nationwide."2
So with that in mind, it's incumbent upon us as gardeners to do two things:
Never buy an invasive species.
Eradicate any invasives we may have in our gardens.
The first is easier than the second, I can tell you! I've spent eight years, and I'm still eradicating bindweed and company from my property. But I have made a significant difference. So we carry on! Want tips on how to get rid of weeds and invasive species? Check out my post on managing weeds.
How to Identify and Manage Problematic Plants
So, how do you KNOW what to avoid? That's the easier part of the equation.
Let's start with what you already have:
Identify every plant on your property. Even the weeds. Someone probably made choices before you got there about what to plant. And you may have chosen plants you now regret (that's ok!). But knowing what you have is important! I like to use the PlantNet app for identification and tracking. It's very helpful!
Make a plan for each plant that you need to eliminate. Some invasives like Tree of Heaven must be eliminated in very specific ways to be successful. Do some research – or talk with your local Master Gardeners – about how to properly eliminate and dispose of your noxious weeds or invasive plants.
Dispose of invasive and noxious plants properly. Just putting them in the trash often isn't enough! For example, Field Bindweed can reproduce from root and stem fragments about an inch long. I can't compost it. And if I put it in the trash before it is dead, I may just be spreading Bindweed further! So after I pull Bindweed, I leave piles of it out to dry. Only when it is dessicated do I put it in the trash – never in the compost, just in case I missed something.
When you are shopping for new plants:
Shop the native plant section first!
Do an internet search using the plant's Latin name and the words "invasive site:edu" (for example: "Buddleja davidii invasive site:edu") before adding that plant to your cart.
If you live near a state line, be careful not to plant species that may be considered invasive in another state.
Resources for Finding Alternatives
There are so many people out there making this easier for us all! Here are a few of the wonderful "plant this not that" kinds of resources available to help us make better plant choices.
We are all in this together!
As Resistance Gardeners we are watching the erosion of the systems we have relied on to protect our environment and ourselves. So we must take on more of that stewardship – piece by piece on our own properties. And part of doing that is learning about what is invasive and noxious in our areas. We must eradicate those species to the best of our abilities. And we must make better plant choices for our environments. It sounds like a lot, but every little bit helps. We can do this!
Remember, your local extension offices are there with Master Gardeners to help! Find yours here. Also consult your local native plant societies, too! Planting natives first can make these choices a lot easier!
Comment Below
If you have struggles with invasive species, let us know in the comments! We can help each other problem-solve. Let us know what has been successful – and where you might need some guidance or advice. And if you have questions, ask!
Happy Gardening!
Angela
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A version of this piece has been published on WildRevivalGardening.com. Republished with permission.
Bureau of Land Management, "About Weeds and Invasives," U.S. Department of the Interior, https://www.blm.gov/programs/weeds-and-invasives/about.
Evelyn M. Beaury et al., "Invasive Plants Are Still for Sale as Garden Ornamentals, Research Shows," University of Massachusetts Amherst, 17 Aug. 2021, https://www.umass.edu/news/article/invasive-plants-are-still-sale-garden-ornamentals-research-shows.
My bane is sweet autumn clematis. Uneducated to its habit, I planted it 30 years ago and am still plucking it from my property. It is hardy, lovely, blooms late, and smells great, but a drive along any interstate in the fall here in the mid-Atlantic clearly shows how it has spread. It's the fall equivalent of its white and scented spring friend and yard escapee, Callery pear.
I have read several articles about keeping dandelions to benefit early pollinators and as food for us (leaves, flowers, buds). I'm curious to hear your take on this.