By Larry Hodgson

Over the last few months, usually after I’ve published a list of plants for various uses (groundcovers for shade, butterfly plants, etc.), I’ve received a few complaints from readers that one of the plants on the list is invasive and that I shouldn’t be promoting invasive plants. I think it would be worthwhile discussing what an invasive plant is to understand why that criticism is unjust. 

So, What Is an Invasive Plant? 

The native mayapple (Podophyllum peltatum) has turned out to be the worst weed in my garden. Photo: James St John, Flickr

From my point of view as a gardener, an invasive plant is one that readily spreads out of control. It can be of any origin, native or exotic. For example, I planted a mayapple (Podophyllum peltatum) in my garden two decades ago and I’ve been fighting to keep it under control ever since. It’s a native plant where I live and, in fact, is considered a threatened species in my province (Quebec), but that doesn’t stop it from being a garden thug. And a plant that spreads rapidly via underground rhizomes and chokes out its competitors, isn’t that the epitome of an invasive plant?

Well, not according to certain government agencies and environmental groups. They seem to have slipped the idea “alien” or “exotic” into their definition, such that it comes out “an invasive plant is an alien plant that readily spreads out of control.” 

To my gardener’s brain, that would be an “alien invasive plant” or an “exotic invasive plant.” I fail to see why a native weed can’t be considered invasive. It just doesn’t make any horticultural sense.

Government definitions, I sometimes feel, are designed to confuse, not to enlighten.

Where Is It Invasive?

Then there is the question of where the plant is invasive. 

Butterfly bush
Butterfly bush is invasive in some climates, but not in others. Photo: http://www.maxpixels.com

Plants are not going to spread endlessly in environments that aren’t suited to them. At best, they’ll hang on. At worst, they’ll die. So, when someone complains that butterfly bush (Buddleia davidii), for example, is invasive and should, for that reason, be removed from a list of plants gardeners can use to attract butterflies, let me point out that it is certainly not invasive everywhere. It tends to need a fairly mild, fairly dry climate. It’s certainly not invasive where I live. It doesn’t even survive the winter here (USDA zone 3) and we grow it as an annual. It can’t possibly spread. 

Other plants that are invasive in some environments and not at all in others include English ivy (Hedera helix), miscanthus (Miscanthus sinensis) and tamarisk (Tamarix ramosissima). Plus, if you accept the definition that an invasive plant is necessarily an exotic one, English ivy would not be considered invasive in Europe, where it is native … even though it can readily spread there. 

There are also cases of plants that could be invasive, but are generally grown as houseplants. Pothos (Epipremnum aureum), for example, could be invasive in a humid tropical climate, and so could inch plant (Tradescantia zebrina), but when they’re grown as houseplants, as they usually are, where is the harm? Plus neither is ever going to be invasive in Paris or Poughkeepsie even if, by some miracle, they found their way outdoors.

Sterile Cultivars

Lantana Bloomify Red
Lantana Bloomify Red is a sterile cultivar and won’t spread. Photo: Ball Flora, National Garden Bureau

Of course, there is also the question of sterile cultivars. There are now, for example, sterile cultivars of lantana (Lantana camara) that can be safely grown in climates where lantanas can be invasive (and need I point out they can only be invasive in tropical climates?). Should I ban even sterile lantanas from any list of plants as well? Already, even fertile lantanas are not invasive for more than 90% of my readership which tends to be concentrated in temperate zones where lantanas are strictly grown as annuals.

Any Plant is Potentially Invasive

If I had to ban from my writings all plants that might possibly be invasive somewhere in the world under certain circumstances, there wouldn’t be much left, would there? 

I’ll bet that if I were to produce a list of fifty “groundcover plants for shade,” given that groundcover plants tend, by their very nature, to spread a bit, at least forty of them could potentially be invasive somewhere. 

And what about useful plants? Many common vegetables are potentially invasive as are a great number of herbs, cereal crops and other useful plants. Should I ban any mention of tomatoes, carrots or wheat from my writings? Where do you draw the line?

Since my blog is read all over the world (and I’m not exaggerating), I’d pretty much have to stop writing about plants if I wanted to avoid mentioning any plant that might be invasive … somewhere … sometimes.

I’m currently considering whether I shouldn’t add to all my articles the following warning: Any plant is potentially invasive. Do you think I should?

Due Diligence

Where I live, and where you live too, I assume, there are plenty of warnings about invasive plants you shouldn’t be planting because they are locally invasive. Indeed, some may even have been banned. So, if I produce a list of plants as part of a blog, a list designed for gardeners all over the world and not just your town or state, might I suggest that you mentally subtract from possible use any plants that might be invasive in your area? It would be unfair to my readers to take plants off the list because they are invasive in California and Mexico if they aren’t invasive in Ontario and Connecticut.

Reactions

I know I’m going to get a lot of flack over this article, but at some point, I have to make this clear. I love writing this blog; it’s a true passion for me, but I simply cannot allow “local interests” to influence every word I write. 

And I think adding the warning “Any plant is potentially invasive” to every blog I produce is just plain silly.

’Nuff said. 

Larry Hodgson is one of Canada’s best-known garden communicators. He has notably been editor-in-chief of HousePlant Magazine, Fleurs, Plantes et Jardins, À Fleur de Pot and Houseplant Forum magazines and is currently the garden correspondent for Le Soleil and radio garden commentator for CKIA-FM Radio. He has written for many garden publications in both the United States and Canada, including Canadian Gardening, Harrowsmith, Horticulture, Fine Gardening and Organic Gardening. He also speaks frequently to horticultural groups throughout Canada and the U.S. His book credits include The Garden Lover’s Guide to Canada, Complete Guide to Houseplants, Making the Most of Shade, Perennials for Every Purpose, Annuals for Every Purpose, and Houseplants for Dummies, as well as nearly 60 other titles in English and French. He is a past president of the Garden Writers Association (now Garden Communicators International) and the winner of the prestigious 2006 Garden Media Promoter Award offered by the Perennial Plant Association. He resides in Quebec City, Quebec, Canada.

15 comments on “What Is an Invasive Plant?

  1. In the Midwest, Burning Bush can be part of a landscape plan while here in NH, it is classified as invasive. In my opinion, an invasive plant can definitely be in the ‘eye of the gardener.’ I once planted Lirope and a small blue fescue grass as border plants in a couple of beds. I then spent more time and effort than I could count to get rid of them when they became invasive.

  2. Standing ovation from me! Thank you!

  3. Teresa Gordon

    As a new gardener I was terrified of planting an invasive plant. I once ripped out a new planting of Beebalm because I read it was a thug. I have long since learned to do my own research and differentiate between truly invasive plants (in my area as you say) and the merely vigorous. Plants that are easy to pull and are no threat to the environment should they escape my garden no longer terrify me. The word ‘invasive’ is used far too easily.

    • I agree; people often call a plant invasive when they actually mean aggressive. “Easy to pull” goes a long way towards distinguishing the two. And I agree with Larry that native plants can be invasive in a garden setting, meaning aggressive and hard to get rid of. A native goldenrod was very difficult to eradicate in a former garden, and now I’m battling Anemone canadensis. The anemone won’t grow in the wild areas of my property, but will totally take over a garden bed if I let it.

  4. There are already better words, like aggressive and vigorous to describe this. “Invasive species” and “invasive organism” means non-native in the vast majority of uses. This is how it’s defined by National Geographic, for instance: https://www.nationalgeographic.org/encyclopedia/invasive-species/

  5. Thanks Larry, I agree completely. I enjoy your writing and only wish I spoke French so I could enjoy even more of it! Your easy-going approach has saved me so much time and back pain, and your book on Annuals introduced me to some really interesting flowers.

    Where I live in Vermont in an old house, in an old town, near every plant, tree, or shrub in the area is on the state invasive list. (Because people 100 yrs ago planted what was new, hardy and vigorous!) When I saw a rose bush seedling coming I was very excited to identify it — maybe it was an old heirloom variety! But of course, it’s just multiflora rose. The trees in the backyard are Black Locust. The bushes are the non-native honeysuckle, or Euonymous, the interesting flower is teasel, the giant thistle is a Scotch Thistle, the maple is the dreaded Norway maple. It’s gotten to the point now where when I want to ID something — I start with the state invasive lists! I even purchased a lilac at the garden center which came with a seedling of the invasive Paulownia tree! And now I found out that even the earthworms are invasive!

    Anyway, keep up the good work.

  6. Donna Birh

    Way to go Mr. Hodgson! I appreciate the energy it takes to create and maintain your blog, which you do in both English and French. The research, writing, photos, and translation all take precious time. The wide variety of subjects you cover and the depth of information presented is sure to keep readers interested. And you do all this with your own touch of humor and style.

    As gardeners, we all have the responsibility to read labels, ask questions and do our homework when planning a garden or adding new plants. Ask your local gardening center, they are the specialists for your area. In case of doubt, leave the plant there and inform yourself properly on its properties before buying it. The problem is that most people plant and then just let things go.

    Someone is giving you a plant? Ask them why. Is it because they have too many? This is a sure sign that it might be vigorous in your area!

    If you don’t want a plant to take over your garden, watch it. Remove the dead flowers before they go to seed, cut off suckers, limit roots using barriers if you see that it is starting to get too vigorous.

    A garden is work. But work with results that will benefit you, the birds, the bees, the environment, and everyone who can appreciate its beauty.

    Happy gardening everyone!

  7. Dandelions are very invasive plant of the genus Taraxacum of the family Asteraceae. Millions of dollars have been spent to remove this plant from lawn, but you can buy the seeds of a hybrid variety & grow it in the garden. One man invasive plant is another man rose. Thanks for another good video.

  8. hmmm . . . Yeah, I get it that the exotics are more of a concern, since they are SO detrimental to the natural ecosystems, but in home gardens, some of the natives can be bothersome also. Redwoods ‘suckers’ (which are watersprouts from basal burls) are really annoying, and can develop quite some distance from the originating tree. If a burl develops on a root below a garden, it is very difficult to dig up. (Severing the root only stimulates more burl development.) In Southern California, the native terrestrial species of Yucca can do the same, and one really does not want to stem on a Yucca shoot in a lawn!

  9. Balsamfir

    The old definition of a weed was a plant in the wrong place. I envy you your podophyllum, but probably wouldn’t want it everywhere either. I have however, also witnessed mislabeled “native” plants take over and smother much more diverse landscapes. Indian cup plant, apparently a prairie native, is a real problem in my wetter climate and outcompetes eupatorium, ironweed and ferns along the river bank. The only thing that beats it is japanese knotweed. When it appeared in my lawn, it took me ten years to kill the one seedling. I currently battle scotch thistle, which is beautiful and bees love it, but I find it very painful to bump into. Researching plants before putting them in is very useful. I once purchased a houtynnia on impulse, but after reading about it refrained from planting it .

    Your comment about location of invasiveness is important. I remember begging a piece of a red leafed spurge from a garden center. They wouldn’t sell it because it was a thug for them, but it has barely survived in my colder climate, and certainly isn’t a problem.

  10. I remember walking past a house with pots of pretty pink flowers in Harlem in the Netherlands and our guide was saying how house proud the dutch were and what a pretty plant it was…..the rest of us were looking at her in amazement as the women was growing Himalayan Balsam, one of the most invasive introductions to Europe and definitely not something that you want in the canals of the Netherlands. We have a few in the UK which are illegal to let grow in the wild and can result in fines and prison sentences for selling them or dumping contaminated soil.

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