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Invasive Plants: What’s A Gardener To Do?

April 8, 2010

imageIn recent years, I have become increasingly aware of the problem of invasive plants. I am not referring here to those uninvited plants (aka weeds) that invade our flower beds and crowd out the plants we are trying to grow. And I’m not referring to plants that we’ve invited into our gardens only to discover that they don’t “play nice” with others (aka “garden thugs”). When I talk about invasive plants, I mean  exotic plants that we invite into our gardens, but that have a propensity to escape from the garden and do serious damage to native ecosystems.

Here in the northeast corner of the United States, three of the most problematic invasive plants are purple loosestrife (Lythrum salicaria), Japanese barberry (Berberis thumbergii), and Japanese knotweed (Fallopia japonica or Polygonum cuspidatum). These are all beautiful plants, and it is easy to see why they were desired by gardeners who had no idea what kind of disaster they were putting into motion.

Purple loosestrife (Lythrum salicaria) is a beautiful plant that can be breathtaking when masses of it bloom together. But those fields of purple are crowding out native cattails and destroying marsh habitats. Photo credit: John D. Byrd, Mississippi State University,

Some gardeners avoid the problem of unwittingly introducing invasive exotics by growing only native plants. I’m not willing to take this route. Although I include native plants in my garden, most of my perennials and many of my favorite plants are, in fact, exotics (some of which have been grown here for hundreds of years). But if I’m going to bring exotic plants into my garden, I have an ethical responsibility to make sure that I’m doing so in ways that do not harm native ecosystems.

After much thought, I’ve identified three steps I can take to garden in a way that is ethical and sustainable:

  1. Educate myself about invasive plants. A browser search for “invasive plants” + a place name (in my case, “invasive plants + Maine”) will usually identify links to government or university sources that list locally invasive plants. Other good sources of information for the United States are the Plant Conservation Alliance, which provides fact sheets for a list of the most invasive plants, and the Invasive Plant Atlas of the United States, which has extensive lists of invasive species and allows you to look at a map showing where any given invasive species is a problem. (Unfortunately, the Invasive Plant Atlas does not allow you to click on a part of the map and see what species are invasive in that location.) Both sources provide information on native plant alternatives.
  2. Take responsibility for invasive exotics growing in my garden. I am not growing any of the plants listed as a serious problem by the state of Maine, but I do have one plant in my garden that may be problematic, Spirea x ‘Magic Carpet.’ Since I first learned that Spirea japonica is invasive in eastern woodlands, I have been engaging in a process of denial and wishful thinking about my beloved ‘Magic Carpet’ shrubs. This plant is sometimes listed as a hybrid of Spirea japonica and sometimes as a hybrid of Spirea bumalda, so I tried to convince myself that it wasn’t really one of those invasive S. japonicas. Then I thought that, since it’s a hybrid, maybe its flowers are sterile. This week, I finally moved beyond wishful thinking and learned the facts about ‘Magic Carpet.’ When I did a browser search on the plant, I quickly found the patent application from the breeder, which clearly lists it as a cultivar of Spirea japonica. I also found accounts from gardeners of self-sown seedlings from ‘Magic Carpet,’ so it’s not sterile. Finally, although the state of Maine does not list Spirea japonica as invasive here, the Invasive Plant Atlas shows infestations of it in one part of Maine, the county that borders mine, about 10 miles away. And my house is surrounded by exactly the kind of woodland that Spirea japonica is known to invade.
  3. Take action to stop the escape of invasive exotics from my garden. Now that I know my Spirea ‘Magic Carpet’ is a potential problem, I need to do something about it. According to the fact sheets, Spirea japonica spreads when its seeds are washed by the rain into wet areas and stream beds, and the seeds can remain viable for many, many years. The first thing I need to do is to stop the seeds from spreading; I can do this by deadheading the spent flowers before they set seed. Since seed may have already spread into the woods, I also need to walk the woods around my house a couple of times a year, looking for signs of Spirea seedlings. By repeatedly cutting any seedlings back to the ground, I can keep them from maturing, flowering, setting seed and invading the native woodland ecosystem.

Faithfully deadheading my Spirea plants and scouring the woods for escaped seedlings is going to take a serious commitment of time and energy; but by making that commitment, I can help to preserve and protect my native woodlands and the species that depend on them. Taking responsibility for my exotic garden plants will also make me more aware of how my garden interacts with the surrounding environment and thus help me to garden in a more responsible and sustainable way.

Thanks to Jan at Thanks For Today for sponsoring the Garden Bloggers Sustainable Living Project. For a list of all the posts that have been written as part of this project, click here.

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60 Comments leave one →
  1. April 8, 2010 11:35 am

    Your post is very informative and I really enjoyed reading it, Jean. I’m so happy you’ve joined in on this ‘project’ and want to thank you for doing so! The topic is so broad and no one person can do everything, but as they say: every little bit helps. Deadheading seed-heads and especially scouring your woods will definitely be a time consumer for you…but with your knowledge and understanding you are choosing to help keep your area sustainable. Too many of us don’t have the information to make good choices. Your suggestions for further reading will help many people think about and become aware of invasives and to take action in the form of not planting them at all, or at least monitoring and keeping a watchful eye out to prevent eventual damage and disaster. Thanks again;-) Jan

    • Jean permalink*
      April 8, 2010 2:19 pm

      Jan, I agree that awareness is key, and not planting invasives is a much better strategy than trying to control them after the fact. The issue was not on my radar screen at all when I added these plants to my garden 8 years ago, after seeing and admiring them in a garden on a local garden tour. Of course, even if I had been paying attention, I probably wouldn’t have identified these plants as a problem. They are not listed as invasive in any of the New England states, and the Invasive Plant Atlas of New England doesn’t even list Spirea in its index. Ground zero for the Spirea japonica problem is your area — New Jersey and Pennsylvania, south through Maryland, Virginia and North Carolina, and west through Kentucky and Tennessee.

  2. April 8, 2010 11:52 am

    A very informative post. Many people have no idea the impact they have on the environment.

    • Jean permalink*
      April 8, 2010 2:24 pm

      Too true, Ceara. Even as I was paying attention to recycling, conservation, etc., I was pretty clueless about the issue of invasive garden plants! Maine, unfortunately, does not have laws against selling serious invasives; as recently as last summer, I saw purple loosestrife for sale at a local nursery.

      Does anyone have a good strategy for raising this issue with nursery owners? I don’t want to just confront them and make them defensive, because I’m not sure that would be effective in getting them to stop selling these plants.

  3. April 8, 2010 12:19 pm

    This is a very interesting and thought provoking post. I admire your dedication to your magic carpet, but I wonder what would happen if you moved away, or were on holiday or not feeling well when the seeds were being formed? I’m not trying to be argumentative at all, I just always think of the ‘what ifs’. Seeds that are viable for years can travel a loooong way, and it would be hard/impossible to track them all. Would you consider looking for a similar replacement to your beloved magic carpet? I hadn’t thought of Spirea as being invasive, I don’t recall ever seeing an out of place seedling.

    About 10-15 years ago I remember seeing posters along the lines of ‘ban purple loosestrife’ with pictures of it COMPLETELY filling what were small waterways, it’s amazing how aggressively some plants can spread.

    I think a post on ‘garden thugs’ would be very interesting, we all have a few of those, and it’s a bit of a love/hate relationship.

    • Jean permalink*
      April 8, 2010 2:31 pm

      Oh dear, Rebecca, I fear that you’re right; I’m still engaging in wishful thinking. I should say that I have never seen any seedlings from my Spirea, in the garden or out of it, so I don’t have any direct evidence that it’s a problem here. As I noted in my response to Jan (above), it’s the mid-Atlantic states that have a big problem with Spirea invading woodland habitats. But, as the climate warms, ours is expected to become more like the current climate of the mid-Atlantic states.

  4. April 8, 2010 1:44 pm

    I echo Rebecca’s concern that you might not always be present when seed heads form.
    I also understand how invasive some varieties off Spirea can be. I dug out two different varieties from my garden because they were self seeding in a manner that I judged to be invasive-and, mine is a city garden. The straw that broke the proverbial camel’s back was when I found Spirea seedlings growing in the cracks of the driveway pavement and concrete sidewalk.

    • Jean permalink*
      April 8, 2010 2:34 pm

      This is disheartening news, Allan — just when I was convincing myself that Spirea might not be a problem this far north.

  5. April 8, 2010 1:53 pm

    Jean, I enjoyed this post. You are right, those plants are so beautiful, it’s difficult to ignore them. I agree with you, we can invite them into our gardens and be responsible for them. If we look closely, a majority of our plants are aliens. If we ignore all of them, we’ll lose a lots of beauties.

    • Jean permalink*
      April 8, 2010 2:38 pm

      Tatyana, I feel quite torn about this. The idea of creating beauty by combining plants from different parts of the world is at the heart of ornamental gardening. On the other hand, once you introduce something new into an ecosystem, it’s hard to predict what else will change as a result. I think I need to go read some of those books on reconciliation ecology that Adrian has listed on her blog!

  6. April 8, 2010 2:38 pm

    Hi Jean~~ I was able to find Lythrum s. at a nursery several years back. It is not the slightest bit invasive in my garden, nor was it at the nursery’s display garden. I believe it’s due to the dry summer soil we experience here. Still, it is outlawed.

    I don’t think those of us that are avid gardeners are the culprits of the invasive plant issue. If a plant gets out of hand in our well-tended gardens, we know what to do and we do it. I believe it’s the naive spring/early summer pseudo-gardeners, [bless their hearts] who are most likely to procure, then abuse the privilege. That said, it’s up to the nurseries to prevent this potentially detrimental scenario by refusing to sell spreaders and prolific seeders . However unless their is a viable punitive threat [monetary fines] many nurseries will keep selling the offending plants. Which makes it a governmental issue meaning it’s up to lawmakers to instate such directives. But most lawmakers are ignorant and/or manipulated by special interests…. Which sort of defaults the responsibility back onto each individual … and the clock keeps ticking….

    This post is not intended to be completely serious or rife with “answers.” I’m not presumptuous enough to believe I have any. Like you, I’ll just take care of my little slice of Earth. It’s a privilege.

    • Jean permalink*
      April 8, 2010 3:24 pm

      Hi Grace, I don’t feel as sanguine about this as you do. I think it depends on how a plant spreads. If it spreads by roots or by seeds that tend to fall pretty close to the parent plant, then we can rest assured that, if it’s not invasive in our own gardens, we don’t have a problem. But I honestly don’t think plants with those characteristics usually become invasive. If a plant’s seeds are spread well beyond the boundaries of my garden by the wind or by birds, then the fact that my garden’s environment isn’t hospitable for the spread of the plant is irrelevant if some of those seeds end up in hospitable environments where they then explode into habitat-destroying infestations.

      I agree that nurseries bear an extra burden of responsibility for keeping invasive plants off the market. I was tipped to the presence of Lythrum salarica at a local nursery by a dissident employee who was watering plants and said that she tried to avoid watering the loosestrife in hopes they would die! But Maine doesn’t have any laws against selling them. All the laws about invasive species here are focused on aquatic plants, some of which are so invasive that they can fill in an entire lake or pond within a few years of being introduced, and tree diseases (forestry is a major industry here).

  7. April 8, 2010 4:59 pm

    Awesome advice. I too have become aware of invasive plants but need to learn more. I inadvertently bought the iris pseudocorus at a garden show last month. It too spreads like ‘Magic Carpet’ into wet areas. I refuse to plant it in the garden but may keep it in a pot on the driveway. Haven’t decided. I don’t want it to smother the ponds here. But I also did good and bought two iris virginicas. Those are easier and I’ll for sure plant them. It is just sometimes really hard to know what is best unless you only buy natives but I’m learning. I’ll take your advice and Google the invasiveness of plants. I didn’t realize you were in Maine. I am from Maine (Brunswick area) and often buy plants there and put them in my garden.

    • Jean permalink*
      April 9, 2010 9:53 pm

      Tina, We should compare notes on Maine nurseries! I’m hoping to do blog posts on some of my favorites as I visit them later in the season. I bring plants back and forth all the time between my garden in Maine and my much smaller garden in Gettysburg, PA (where I teach). It’s amazing how many plants are happy to live in both these fairly different environments.

  8. April 8, 2010 5:32 pm

    Thanks for this very useful information that can be adapted wherever we are Jean. Blackberry is one of the biggest garden escapee problems for local bushland in my part of Australia. Birds spread it very easily and people sometimes dump it in the bush.
    I remember seeing a UK documentary about Japanese Knotweed and thinking we were so lucky not to have it here. Then at the recent Melbourne Garden show we visited the Weeds Australia stand and I discovered it had been introduced (I’m guessing by accident, customs wouldn’t have let it in willingly). This is one of half a dozen weeds in Victoria that they are so concerned about that they have a ‘dial don’t dig’ policy for it.

    • Jean permalink*
      April 9, 2010 9:58 pm

      Heidi, Now I understand why blackberries invade your garden, while mine are a bit of a nuisance but stay mostly around the edges of the woods. It’s interesting that a plant that is a bit of a pest but manageable in one place can become invasive when moved to a different environment. After I read your comment, I looked up blackberries on the Invasive Plant Atlas and was surprised to find that my native eastern blackberries are a major invasive problem in Hawaii.

      I’m interested in Victoria’s ‘dial don’t dig’ policy. Do they want people to get advice about how to remove the plant before they take it on?

      • April 9, 2010 10:48 pm

        Hi Jean,

        The ‘dial don’t dig’ policy is applied only to the worst of the worst (knotweed, horsetails, orange hawkweed…) that they hope to still have some chance of controlling. I think in some cases advice is given, but in many cases an officer from one of the weed control agencies or local council will visit and determine if the weed needs professional removal and monitoring.

        Your informative post prompted me to start exploring the Weeds Australia website and it is a very good one if you are interested in having a peek

        As for our blackberries – I think the open bushland of Southern Australia suits them just a little to well!

        • Jean permalink*
          April 10, 2010 2:06 pm

          Heidi, Thanks for the link. I was particularly struck by the inclusion of orange hawkweed on your list of the “worst of the worst.” It brings home to me again the point made by Helen (below) that what is invasive depends on where you are. I think of orange hawkweed as a charming and relatively rare wildflower; I have taken photos of it when I encountered it while hiking! I actually thought it was a native here, but it turns out that it was introduced to North America by European (British?) settlers, as it presumably also was to Australia. I wonder if they introduced it on purpose as some kind of herbal or if it just tagged along on ships.

  9. April 8, 2010 6:43 pm

    We have quite different invasive plants here, but I am just beginning to educate myself, Jean. Bravo to you for taking action and making a commitment. Although I do have to mention, the time to worry is after you’re gone. Whenever I see the worst instances of non-native takeover, it is around old, abandoned houses. 😦 In fact, I’ve lately been pointing out to F. how bad the local problem with bamboo is… ever since he made the mistake of asking if I knew where we could source green and flexible bamboo. It’s truly omnipresent, and though the sometimes thirty-foot high stalks are lovely bending in unison in a stiff breeze, it’s still sad to see them obliterating native forest in their path.

    • Jean permalink*
      April 9, 2010 10:08 pm

      Meredith, Thanks for the reminder that I have to take some responsibility for what happens to my plants after I’m gone. Right now, I don’t know that my Spirea is a problem. It’s the species Spirea japonica that’s been identified as a problem, and I don’t know if the ‘Magic Carpet’ cultivar shares the aggressive tendencies of its parent. That’s why I’m treating this as a “potential problem” and I’m in “alert” mode rather than “eradication” mode. My goal at the moment is to keep an eye on this plant and take precautions while I try to gather more evidence. At present, even the parent plant is not listed as invasive in New England (despite those reports of infestations in the neighboring county). But I figure by the time a plant makes the list, it’s already a major problem. I want to gather my own evidence (any seedlings in my woods?), find out if the areas with a problem in the next county have similar soil conditions to my area, and find out if anyone in the mid-Atlantic region has any evidence about this cultivar.

      Given your cautions and those of Rebecca and Allan, I think if I get any evidence that this cultivar is likely to be a problem in my area, I’ll have to remove those plants.

  10. April 8, 2010 7:28 pm

    We suffer from Garlic Mustard. the Ohio Dept of transportation thought that they would do well along highways for erosion control. The Cuyahoga County Soil and Water Conservation District has seminars educating anyone who comes to the dangers of invasive plants. These invasive plants completly devastate the local environment by eliminating the home of native plants, insects, birds, well you get the picture. Pat and I are limiting our purchases to native plants. jim

    • Jean permalink*
      April 9, 2010 10:11 pm

      Jim, Wow! This seems like a big change for you from all those Asian hostas and ligularia — but I bet there are a lot of natives that will complement your existing plantings beautifully. It’s great that your county is sponsoring education programs on invasive plants.

  11. April 8, 2010 9:41 pm

    Hi Jean,
    Great post. In the Midwest we have the Midwest Invasive Plant Network, which gets the news out around here. And Jim, garlic mustard is high on the Illinois list of most hated. Did you know the roots are allelopathic? You can make pesto out of it, so I keep waiting for somebody to realize what a resource it is and go into business. 🙂

    Buckthorn and multiflora rose are illegal in Illinois, and privet and barberry are becoming a problem.

    I used to work at an independent garden center and part of my job was to make sure we didn’t buy invasive plants–but the big box places aren’t going to be so responsible. The same goes for growers–some more responsible than others.

    The other issue with some exotics is that they can be well-behaved for years, then suddenly turn evil and no one knows why. It might be any of a number of factors. Perhaps this happened with spirea?

    • Jean permalink*
      April 9, 2010 10:20 pm

      Very interesting, Adrian! I had to look up “allelopathic.” 😉 It turns out that buckthorn, multiflora rose, and garlic mustard are all on the “serious invasive” list here, too.

      I was struck by your last point that plants continue to evolve and to change their behavior, so we can’t just put a plant in the “good” or “bad” column and forget about it. This really is about developing a type of consciousness of this issue.

      Do you have any suggestions about how to raise the issue of invasives with independent nurseries that are selling them? I don’t want to alienate these local business people, but I would like to raise their consciousness. I realize that the big box stores are a tougher nut to crack because they buy plants from big wholesalers and then ship them all over the country, whether appropriate or not. (It is the big box stores that are widely blamed for wiping out most of the tomato crop around here last summer by shipping plants from Georgia that were infected with late blight.)

      • April 15, 2010 2:23 pm

        This is such a big topic. Little did I know that Vinca is considered invasive in the southern U.S. I’ll have to keep an eye on mine.

        Regarding independent nurseries, one could try speaking with the manager and/or owner, since they have direct control over the ordering. Who knows what to do about big boxes? Some irresponsible growers will offer invasives for sale and unsuspecting garden centers will order them, genuinely not knowing they’re invasive.

        It’s truly a question of education. When customers asked me about a particular plant or other, I would explain that we didn’t sell them because they were invasive, and would they like to try this substitution? Usually customers were grateful for the knowledge and would buy the plant I suggested. It is possible to be ethical and still make sales.

        Sometimes there’s too much assumed separation between the domains of “gardening” and “conservation,” with a concomitant belief in the separation between one’s own garden and the natural ecosystem “out there.”

        Part of the problem seems to be that so many large “industrial” growers sell and ship across state lines. Perhaps some re-localization is in order, as is happening in agriculture with local farmers’ markets vs everything shipped from California? I currently buy my plants from region-specific nurseries that specialize in native plants

        • Jean permalink*
          April 16, 2010 9:20 pm

          Thanks for the advice, Adrian.

  12. April 8, 2010 9:44 pm

    This was a great post. You sure sound like a responsible gardener, especially going into the wooded areas to look for the seedlings. I love that more and more people are using native plants, and less of the invasives. It still bothers me when I see plants at nurseries that become very invasive and they show the pretty pictures to convince people to buy them.
    I had no idea that ‘Magic Carpet’ was so invasive there.

    • Jean permalink*
      April 9, 2010 10:24 pm

      Catherine, Talk is cheap; don’t congratulate me until we see how well I do actually following through on this commitment!

      I don’t want to leave the impression that the ‘Magic Carpet’ cultivar is particularly invasive. It’s actually the parent species, Spirea japonica that has been identified as invasive, and not yet in New England. But, since Spirea japonica is a serious problem in the neighboring mid-Atlantic region, since localized problems with it have been reported in Maine, and since I don’t know whether the ‘Magic Carpet’ cultivar shares this characteristic of its parent, I think I’d better err on the side of caution.

  13. April 8, 2010 9:55 pm

    The other day I was in lowe’s and they had a carts of vinca minor there for sale. That plant is on the top of the South Carolina invasive species list! (its not kudzu, but it does show up on that same short list!) How could they be allowed to do such a thing????? It makes me think that the state and the country aren’t that serious about invasive species if they continue to allow the sale of it.

    We also have wisteria here that have taken over whole small towns. Sure does look pretty though. You can probably buy that at lowe’s too.

    • Jean permalink*
      April 9, 2010 10:28 pm

      Jess, This seems to come back to Grace’s point that there is only so much individual gardeners can do to control invasives — that the real change has to come at the state government level in the form of laws with teeth in them and serious enforcement efforts. Maybe those of us who are concerned about this and whose states don’t outlaw the sale of invasives should start lobbying state legislators. (I bet the big box stores would spend some serious money to lobby against such laws, though, since it would be a major problem for their business model to have to ship different plants to different stores.)

      • April 11, 2010 5:20 pm

        Thats not a bad idea. Its sort of insane for the state government to spend all this effort to try and inform consumers and create websites etc but then not do what they are supposed to be doing and legislate something that will stop the large part of the issue. As far as big box stores I agree they might fight, but there are plenty of products that can’t be sold in California, for instance, and sure enough, they manage to pull it off.

  14. April 9, 2010 9:18 am

    Jean it sure has become a problem, and we all need to educate ourselves on these kinds of plants.

    • Jean permalink*
      April 9, 2010 10:32 pm

      Thanks for stopping by, Keewee. Since I’m a professional educator, I guess it makes sense to me to begin with education. Although I think Grace and Jess are right that education probably needs to be combined with political action.

  15. April 9, 2010 11:00 am

    Hello Jean,

    What a great topic to address. Many gardeners do not think about invasive plants and the damage that they can do to the surrounding area. I like to think that each small invasive plant that you pull, will keep them from reproducing….therefore preventing 1,000’s of them in your surrounding area in the future. We would all do well to follow your example in our own areas.

  16. April 9, 2010 7:22 pm

    Great post Jean. I’ve never been more aware than living here how critical some plants are to the environment, vs. those that can wreak havoc within the ecosystem. Two big bullies here are Vinca Minor, and French Broom, they’re well entrenched, but we’re making every effort to remove both for the benefit of the native plants and animals here. I think as gardeners we all have a responsibility to keep our landscapes under control.

    • Jean permalink*
      April 9, 2010 10:36 pm

      Noelle and Clare, Thank you both for the reminder that individuals can make a difference.

      Noelle, I love your point that every invasive we pull up can prevent thousands of new plants. I also think we live in a culture that makes it difficult for people to see the impact of their actions on a larger community. This connects a bit with my research on virtual community, because I’m starting to think that we mostly define gardens as part of the private sphere — which again makes it more difficult to think about our gardening choices as having consequences beyond the boundaries of our gardens.

  17. A Garden of Threads permalink
    April 9, 2010 9:51 pm

    A great post, I am very careful what I plant in my garden. Vinca minor is a problem in our area and has taken over from native woodland plants in many forested areas. Manual pulling is the only way to remove it. Thank you for reminding us to be knowledgable about what we plant in our gardens.

    • Jean permalink*
      April 9, 2010 10:40 pm

      Thanks for visiting and for sharing your thoughts.

  18. April 9, 2010 10:54 pm

    What a great post! I commend you for taking responsibility, and for educating yourself.

    Quite frankly, it completely escapes me why people are so very insistent on having those 5 or 6 plants that are a problem where they live. There are hundreds, but it has to be the one.

    I guess it started with Eve in the garden. The one plant that’s not so good for you is the most attractive… Let’s hope more people move beyond that.

    • Jean permalink*
      April 10, 2010 2:12 pm

      I wonder how many people knowingly plant invasives? I imagine that, most of the time, people just aren’t aware that something is invasive when they plant it. Even worse is the situation where something isn’t identified as an invasive until after you have it in your garden. And if you’re in love with it by then and it hasn’t behaved badly in your garden, it can be difficult to give it up. My Spirea is an interesting case in point. It’s status is ambiguous; is it invasive or isn’t it? And, since it is an anchor plant in my garden, with a major perennial border designed around it, I really want to give it the benefit of the doubt.

  19. April 9, 2010 10:57 pm

    This was a very informative post Jean. So much to learn. I have been trying to learn more about natives myself. From what I’ve read in Fine Gardening mag, the problem with invasives is that it really depends on where you are. The smaller nursuries could know what not to sell but the big box stores just probably send out the same plants to each store no matter where it is. There should, as has been mentioned, some way of regulating what is sold or at least educating the sellers.

    • Jean permalink*
      April 10, 2010 2:22 pm

      Helen, I think you’ve hit the nail on the head about why the issue of invasives is so difficult. It would be so easy if we could just have a definitive list of invasive plants and bar them everywhere. But, instead, a plant that is reasonably well-behaved or even highly valued in one place turns out to be invasive when it is transplanted to a different ecosystem. Just out of curiosity, I looked up kudzu — which is synonymous with “out of control invasive” in the United States. It turns out that this plant has all kinds of beneficial uses and properties and that those who planted in in the southeast U.S. for erosion control or to fix nitrogen in the soil probably never anticipated what would happen next.

  20. Elephant's Eye permalink
    April 10, 2010 3:02 pm

    Another issue with invasives is fire. We have a Mediterranean climate like California, so wildfire is a problem. The natural fynbos is mostly shrubby, burns quickly, and allows the next generation of plants to survive. Even if it is only as seed. BUT the invasive aliens like Australian wattles and eucalyptus, and pine trees – burn HOT. Destroy plants and animals, and sometimes even the seedbank in the soil. And only recently has it been legally enforced, that you cannot sell land, before you clear the invasive aliens. Not always enforced, but at least the intention is there.
    My worst problem in the garden is Paterson’s curse – – which is also a huge problem in Australia.

    • Jean permalink*
      April 10, 2010 5:28 pm

      Diana, Thanks for sharing these observations about fire. I hadn’t even thought about what happens to fire-adapted ecosystems when plants that burn differently are introduced.

  21. April 10, 2010 4:24 pm

    jean, Good afternoon~~and a very excellent post! We went for a walk this morning and despaired to see the dirty diapers and fast food trash that was left in the parking lot of a park near our downtown area. I wonder if your average American is ready to take responsibility for their impact on the earth…Then we get into our yards and gardens and you get a whole other…”Don’t tell me what to do with my property mentality” Last year I spoke with the manager of a big box store (bbs) outdoor department and asked her if there was anyway they could stop selling plants on the Tennessee Invasives List (eonymous, vincas, etc) She told me that it was the public’s fault that her store sold invasives. The public wants them! I suggested that BBS could launch an education program!…You know how it went! In the meantime, I pay attention to what’s on our invasive list and other states in the southeastern US…since they are frequently more proactive then TN! I did notice that kudzu is now listed on the potentially invasive list in the Northeast…

    As to managing the bush honeysuckle, vincas, euonymous, etc., that are already in my yard from previous owners and bird dropping …I often feel like I’m painting the Golden Gate Bridge…I get to the end of the yard and have to turn around and start over. gail

    • Jean permalink*
      April 10, 2010 6:16 pm

      Gail, These are depressing, but important, observations. The fact that individualism and privacy are valued so much more than community in American culture makes the issue of invasive plants that much harder to deal with. Add to that a business climate in which the highest ethical responsibility of the corporation is to make maximum profit for the shareholders, and it’s hard to know where to break into this problem.

      I feel a little bit more hopeful about being able do something with small independent nurseries here. Maine has a fairly well developed environmental ethic (related to the particular brand of tourism that the state markets) and these local businesses owners usually have a sense of responsibility and commitment to the community. Taking on the big box stores will probably require help from big national environmental organizations. (In looking at the organizations associated with the Plant Conservation Alliance, I’m struck by how many of the environmental heavy hitters — e.g., Sierra Club, Natural Resources Defense Council, Environmental Defense Fund — are absent from this list. Maybe those of us who are members of such organizations should start lobbying them to get this on their agendas.)

  22. April 11, 2010 12:01 pm

    Dear Jean, what a very informative and thought provoking post. I have no idea what plants are considered invasive here so your post has encouraged me to research this. Thank you.

    • Jean permalink*
      April 11, 2010 12:59 pm

      Nina, Thanks for stopping by. Just out of curiosity, I did a quick google search on “invasive plants + UK” and there seems to be quite a bit of good information available. If even a few people are encouraged by this post to learn more about invasives and to avoid planting them, I feel as though I’ve made a contribution to the effort.

  23. April 11, 2010 6:39 pm

    An informative and intelligent post, Jean. The thing is, as others have observed, what is invasive in one locale is sometimes barely hardy elsewhere. I remember reading that Chinese forget me not is considered invasive in some areas; here it’s an annual, self seeds a VERY little, and dwindles out. Goosenecked loosestrife is inclined to roam in many gardens, but in my wet clay soil, it died out. Twice.

    It’s hard to say how much climate change is affecting plant hardiness–or will affect it in the future. Perhaps more plants will become invasive, while others die out.

    I do look to the nurseries and plant breeders to take responsibility for some of the problems with invasives. Rosa multiflora, after all, is used as a rootstock for many grafted roses just because it IS so vigourous. Then we wonder why we see it growing in so many locales. Goutweed is a bad, bad plant everywhere, as far as I can see, yet nurseries continue to sell it because it’s virtually costfree to produce. It’s not so bad when in variegated form, but when it reverts to all green, all hell breaks loose.

    Not being a pollyanna here (well, no more than usual), but I do try to look on the bright side with some invasive plants. They can be sources of nectar and pollen for beneficial insects, and of seeds and fruit for wildlife. I’m not into planting only natives (which aren’t the answer to all of life’s questions either, though I have more than 150 native species growing on my property), but I do advocate learning as much as we can about invasives–for our area–as possible before planting something new.

    That said, I wonder why we can’t be overrun with orange echinaceas and blue poppies? That wouldn’t be so bad… 😉

    • Jean permalink*
      April 12, 2010 8:19 pm

      Hi Jodi, I’ve been using a fairly narrow definition of invasive: exotic plants that escape from the garden and whose aggressive behavior outside the garden does serious damage to native ecosystems. So by this definition, invasives are always a net environmental loss; they provide fewer resources to local fauna than the plants they drive out would. I think most invasive lists in the US use criteria like these, but I don’t know how invasive plants are identified in Canada.

      The whole issue of climate change really does make the issue of invasive plants even more complicated. Inevitably, as conditions warm (and, in some places, also become wetter or drier), some plants will not survive the changes and other plants will move in. Maybe one way to identify which of these plants might reasonably be considered invasive is to look at invasive lists for places that currently have the climate we are expected to inherit. In New England, for example, they tell us that our climate will become like that of the mid-Atlantic region. (Which is another reason to keep an eye on my Spirea japonica, which is currently invasive in the mid-Atlantic region.

      Thanks for adding your very thoughtful perspective.

  24. April 12, 2010 7:26 am

    It’s always alarming when we find we have introduced an invasive plant – as we did with autumn olive from the Conservation District. Even they make mistakes. The original plants died, but not before seeding in the field nearby. We are at work eradicating. At least I didn’t introduce all the multiflora pasture roses that we continually battle.

    • Jean permalink*
      April 12, 2010 8:24 pm

      Pat, Thanks for reminding us that, as long as we continue to invite new plants into our gardens, we run the risk of making some mistakes and including plants that turn out to be invasive. Thanks also for reminding us that, if we are vigilant and catch those mistakes early, they can be remedied.

  25. April 12, 2010 8:58 am

    Thanks for a very informative post and ensuing discussion on this topic. I’ve also recently gotten interested in the subject, upon discovering that a few plants I had always regarded as quasi-native are actually considered invasive! One of these is buddleia, omnipresent in German gardens and beloved of all gardeners. I think it’s very interesting that an invasive plant from another continent can sometimes be so very appealing to native fauna – buddleia is a case in point. So I’ve decided to go your route: keep my buddleia, but deadhead it diligently. In the case of lantana, which I also love because of the way it attracts butterflies and bees, I’m not worried, since it seems to only be considered invasive in places with mild winters. But I guess it’s still debatable whether or not it should be sold by nurseries, since that creates a market that might spread beyond a given area.

    • Jean permalink*
      April 12, 2010 8:26 pm

      Barbara, Thanks for weighing in on this. I believe that an earlier post of yours asking for opinions about the issue of invasive plants was instrumental in getting me thinking about this issue.

  26. April 15, 2010 9:53 am

    I didn’t know that my ‘Magic Carpet’ spirea would be a problem. I have three of them, and they are gorgeous! I’m a faithful deadheader, so I usually don’t leave much behind.

    Thanks for the information!

    • Jean permalink*
      April 16, 2010 9:18 pm

      Jennifer, Thanks for visiting. Spirea japonica is mostly a problem in the mid-Atlantic states, where it escapes from gardens and takes over woodlands. You’re in Mississippi, right? I checked the Invasive Plant Atlas, and Spirea japonica is not listed as invasive there. There are a couple of counties in Louisiana that have reported problems and one county in eastern Alabama, but otherwise no reports of problems near you. I think you’re in a similar situation to mine; we just need to be aware of the potential for this plant to be a problem, take precautions (like deadheading), and keep an eye on the situation. It’s probably more of an issue for me than for you, because the Spirea infestations are more likely to move north than to move south as the climate warms.

  27. JR Harris permalink
    April 13, 2016 3:18 pm

    What’s going to happen to the root structure left in the Woods by your spirea after you’re gone. Will cutting them off at the ground twice a year stop them from spreading on out into the woods around your place if those roots are still alive 50 years from? How do you know one or two of them hasn’t escape your vigilance?

    • April 13, 2016 10:33 pm

      JR, These are important questions. When I wrote this post, the jury was still out on whether this particular cultivar of Spirea was fertile or not; now, thanks to some very careful research on Spirea cultivars done in Montana, we know that it is. Where this plant is invasive, it spreads by seeds. I have had this growing in my garden for more than ten years (long before I knew it was a potential problem) and I have never seen a single seedling. One reason may be that the primary method of seed dispersal is by water, and I garden on dry, sandy uplands where it is unlikely that the seeds from my plants will end up in water. (The big problems here tend to be plants that are dispersed by birds, like the Tartarian Honeysuckle that keeps showing up on my property, spread by birds from an infestation along a stream about 1/2 mile from my house.) Nevertheless, I realize that I need to monitor this plant and keep abreast of new information about its invasive tendencies. I would like to add another spirea to my garden, and I am looking at some of the cultivars that the Montana study found to be sterile.


  1. Toward a More Earth-Friendly Garden « Jean's Garden
  2. Rethinking Invasive Plants | Jean's Garden

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