Invasive Plants

by John Bandler

Invasive plants are bad for many reasons and they are literally taking over. Better education and awareness can help us fight them. Plants are an essential part of our ecosystem and are essential for every species living on this planet.

A silver lining of the COVID pandemic is that I was able to live in the countryside and observe nature and plants on a daily basis. Previously, I visited only occasionally. With daily monitoring I saw my plantings wake up in the Spring and grow. I realized how some weeds seemed to be taking over the landscape despite my longstanding efforts against them. After this observation I started researching and obtained some expert advice. I learned about invasive plants and our environment, and wish I had learned this thirty years ago because the property would be different now. We can't go back in time, but we can improve our future.

This article can jumpstart your knowledge and learning on the topic.

An invasive plant takes over and damages ecosystems

Evolution is a process which has been occurring for millions of years, and plants and animals evolved in various regions to create ecosystems that were in balance. Each species has mechanisms to grow and reproduce to ensure survival of the species. Plants generally need light, water, and carbon dioxide to grow and reproduce by seed or other means. Animals and insects need to eat, grow, and reproduce too. Insects need plants. Many animals eat plants, some eat other animals.

After millions of years, species evolved within ecosystems and balance was created. Many species can coexist and be integral to the overall cycle of life. Certain plants can grow together, some animals eat certain plants, some animals prey on other animals. Evolution and change always occurs, but at a crawl, over hundreds or thousands of years. The ability of plants and most animals to travel is limited.

Then came humans. Accidentally and deliberately we have transported species from one location to another, introduced them into an entirely new ecosystem. Sometimes they find conditions with no natural predators or mechanisms to keep them in check. They reproduce and spread voraciously, choking out native species. They serve little or no benefit in the new environment and almost always cause serious harm. They are an invasive species in the new ecosystem.

"Weed" is an imprecise term reflecting human opinion

A "weed" is simply a plant growing where it is not wanted. It is an imprecise term reflecting human opinion about a plant. Human opinion is not always "correct", and people's opinions differ. One person's "weed" is another person's beloved plant.

A good first step is to identify that plant we call a "weed". And use the name. That we we move past the subjective term of "weed" which means different things to different people.

An invasive plant is always harmful, and thus should always be managed.

Invasive plants get the designation from scientists (and government groups) after careful evaluation of their impact on the environment. Every invasive plant should be considered a "weed". But not every "weed" is an invasive plant.

Almost all native plants are an important part of the ecosystem, but some people sometimes consider them "weeds". Sometimes this is fine, sometimes this can have effects on the environment. If we are managing our garden, planting beds, or landscape, we can encourage our plantings and weed out undesired weeds.

Sometimes we can be better informed about what we consider a weed. For example, milkweed (asclepias) has "weed" in the common name and some have sprayed it with herbicides to kill it. But now many realize it is an important native plant that provides essential benefits for the ecosystem, including for insects and monarch butterflies. A lawn filled with native "weeds" may be beneficial to many insects, including bees and fireflies and more.

The harms caused by invasive plants

Invasive plants can crowd out every other plant, including the native plants that insects and animals in the region rely upon. Invasives degrade the environment and native insects and animals find their resources are diminished. Butterflies may require certain host plants to lay eggs on and for nectar, but if that host plant has been crowded out by invasives, that butterfly will not be able to grow and reproduce.

Vast swathes of our environment are being overtaken by invasive plants. What was once a balanced ecosystem is degraded. Native plants choked out, vines choking trees, native plants suppressed and native insects and animals unable to find the foods and nectars they need. Private lands and public lands degraded.

We do not need to accept this as the new normal. It does not need to be this way.

Examples of invasive plants

There are invasive plants in every region and state. My experience (as a layperson in the field) is with the New York and Connecticut area. As you learn, familiarize yourself with what is invasive in your region.

Having learned about them on the property where I garden, I now realize they are everywhere: along roadways, on public lands, on private property.

Let's talk more about terminology and naming. Plants (and all species) have "common names" which are like nicknames, they are imprecise and vary from region to region and person to person. Plants also have "scientific names", which are Latin, harder to learn and remember but unique and precise. To fight an invasive plant we want to properly identify it -- be able to state the scientific name and common name(s).

In my family, we misidentified many plants for many years, and that hampered our progress. As with all things in life, one needs accurate facts to make good decisions. You need to know what it is to know if it is invasive or not, and how to fight it.

Here is a quick list of some of the weeds I have researched and worked to combat. (Some day I may build out additional pages for each).

  • Bishop's Weed, Goutweed, Ground Elder, Aegopodium podagraria (for over a decade we mistakenly thought this was Queen Anne's lace)
  • Oriental Bittersweet, Chinese bittersweet, Asian bittersweet, Celastrus orbiculatus
  • Porcelain Berry, Ampelopsis glandulosa
  • Multiflora Rose, Rosa multiflora
  • Wineberry (wine raspberry), Rubus phoenicolasius  (for two decades we mistakenly thought these were wild raspberries)
  • Japanese Barberry, Berberis thunbergii
  • Autumn Olive, Elaeagnus umbellata
  • Garlic Mustard, Alliaria petiolata
  • Common Reed, Phragmites australis
  • Oriental Lady's-thumb, Polygonum caespitosum, or Persicaria longiseta
  • Japanese Stiltgrass, Microstegium vimineum
  • Burning Bush, Euonymus alatus  (I confess I have planted this, but have removed it)
  • Japanese Knotweed, Japanese bamboo, Polygonum cuspidatum, Fallopia japonica
  • Dame's Rocket, Hesperis matronalis (we mistook this for phlox, it is beautiful but terrible for the environment)
  • Norway Maple, Acer platanoides (me mistakenly thought this was a good Maple, a large professional arborist company even took money for pruning them without advising us that it was an invasive tree species)
  • Privet, Ligustrum genus
  • Tree-of-heaven, Ailanthus altissima
  • Mugwort, Artemisia vulgaris L.
  • Wild Grape, Vitis Spp  (this is not technically an invasive plant, but worthy of control)
  • Poison Ivy, Toxicodendron (not an invasive plant, but worthy of control in my opinion).

How to combat invasive plants

Fighting invasive plants requires knowledge of horticulture, biology, and science. With this knowledge, one can develop a good strategy and then be persistent with implementation. Plan for a long war against an invader, not a quick fix. In other words, have a good strategy for the long term and good tactics for the short term operations.

Here's a plan overview:

  • 1. Properly identify the invasive plant
    • Identify the scientific (Latin) name, as well as various common names
    • Research photos from reliable sites to identify it at various stages
    • Recognize it at various stages
  • 2. Learn about the invasive plant
    • Is it an annual, biennial, or perennial?
      • Annuals live for a single year, drop seeds, and the seeds sprout the next year.
      • Biennials live for two years, drop seeds, the seeds sprout
      • Perennials can live for multiple years, and may spread by seeds or roots (or rhizomes)
    • How does it reproduce (propagate) and spread?
    • What does it like?
      • Most plants like light, water, air, nutrients
      • Some have special requests
      • Most plants like to be left alone to grow and reproduce
    • What does it hate?
      • Most plants don't like to be smothered, cut, or pulled
      • Some things damage or kill certain plants
      • Certain herbicides will kill certain plants (applied at the right time)
  • 3. Develop a long term plan that is practical and sound and that you can stick with. This is a long-term process over many years.
    • Your plan needs to be horticulturally and scientifically sound.
  • 4. Take short term actions that are practical and sound and efficient
    • As above, your actions need to be horticulturally and scientifically sound.
  • 5. Monitor and assess and repeat and adjust.
  • 6. Learn about horticulture, gardening, and the environment throughout.

Below are more details.

Strategic thoughts

  • Properly identify the invasive plant. If you don't know what it is, you cannot fight it properly. Proper identification means knowing the scientific name (Latin name) of the plant, in addition to the various common names.
  • Once properly identified, research expert advice available from scientists, biologists, and respected resources.
    • Educational institutions, government resources, invasive plant working groups are usually reliable sources.
    • Use caution reviewing advice not backed by science, horticulture, or proper sources.
      • My guidance here is reasonable and backed by research, science, and reason and is a good place to start. But see what the experts say (links below).
      • Some blog posts, webpage comments, and even articles are just not reliable.
  • Don't plant invasives.
  • Don't spread invasives or allow them to spread (see next).
  • Learn how the invasives propagate (reproduce). Is it by seed, by underground rhizomes or roots, or both? If you know how they propagate, you can work to prevent them from spreading.
  • Learn what they like, and what they don't like, and when.
    • All plants generally need certain things (light, air, water, nutrients).
    • Most plants do not like certain things (certain herbicides, smothering, etc.)
    • Each plant has specific attributes (certain herbicides that work, tolerance for certain conditions).
  • Work to weaken, control, and eventually eliminate the invasive plants, while keeping conditions suitable for native plants.
  • Controlling invasive plants may require a combination of mechanical, cultural, and chemical (herbicide) control.
    • Mechanical control means things like cutting, pulling, smothering.
    • Cultural control means changing human behaviors and habits; what is planted, mulching, watering, etc.
    • Chemical control means application of herbicides and pesticides.
      • Herbicides may have some negative attributes but consider the big picture and greater good. Invasives do great damage to our environment and many cannot be controlled without herbicides. Where required and properly applied, herbicides are necessary to control invasive plants.

Tactical steps

  • If the invasive plant spreads by seed, then you need to:
    • Prevent it from setting seed (cut, pull, or spray before seed set)
    • Prevent seeds from dropping into the soil (pull plant or seed head)
    • Reduce the likelihood that existing seeds in the soil will germinate (avoid turning the soil, cover the soil with newspaper, cardboard, and mulch)
  • If the invasive plant spreads by rhizomes and roots, then you need to:
    • Prevent it from spreading (don't transplant anything from the area, don't move soil)
  • Work to weaken and eventually kill the plants
    • Killing the plants are the ultimate goal, but sometimes it can be difficult or impossible to achieve immediately.
    • Weakening the plants is a first step. This can reduce its propagation, spread, and dominance over neighboring plants.
    • Avoid digging. Digging can bring seeds to the surface for germination, and spread roots or rhizomes.
    • Consider smothering. Smothering roots and rhizomes is an excellent way to kill certain plants, and smothering of seed infested soil prevents germination of seeds.
      • Smothering can be done with newspaper and cardboard with woodchips on top. The smothering effect will last for a few years until the paper decomposes.
      • Avoid landscape fabric or plastic sheeting, unless you resolve to remove it within a few years.
    • Consider cutting. Cutting the top growth removes an important source of energy for the plant. Then the plant must expend energy from the roots to regrow it. This may not kill the plant, but will weaken it.
      • Imagine an Oriental Bittersweet vine that has grown for 20 years, reaching the top of a fifty foot tree to gather light and smother the tree.
        • Cutting the vine at the base robs the invasive plant of all the future sunlight energy those leaves would otherwise capture. It forces the roots to expend great energy to regrow, and gives the tree a chance to recuperate. The invasive plant will live and resprout from the roots, but it is weakened.
        • Some experts recommend to cut the vine and paint the cut with herbicide, which can kill the roots. That is good if you can do it or have a team where one person cuts, and the other follows with the herbicide. But it can be hard to do this in practice because it is an extra step. Sometimes you need to do "good" and don't have time to be perfect.
        • The top of the vine, all tangled in the tree, will die and eventually fall apart over time. Pulling it out could damage the tree. Having a professional climb up to remove it is costly.
    • Consider pulling where appropriate. Some invasives can be hand pulled. For others, the roots are too strong to pull, or hand pulling is of little practical use because roots and rhizomes remain.
    • Herbicide. Properly applied herbicides are important to fight invasive plants. (Yes, some herbicides are dangerous to people and impact the environment, but invasive plants also do great damage to the environment).
      • The herbicide needs to be suited for the particular species of invasive plant, applied at the right time of year, and applied properly.
      • Use the right herbicide on the proper invasive plant, at the right time. Read the label and research.
      • Some herbicides include: Glyphosate (RoundUp's older formula, etc.), Triclopyr, Fenoxaprop
        • Glyphosate may be out of favor, with substitutes available.
      • Avoid overspray onto other plants.
      • Where overspray is a risk due to nearby plants you want to save, and where herbicide is required, consider painting the herbicide onto plant leaves where practical.
        • With a coffee can sized container, herbicide, and a paint brush, invasive plant leaves can be painted or soaked with minimal impact on friendly plants. I am doing this on Bishop's Weed and it seems effective (hand-pulling has proven to be merely a temporary control measure).
  • Monitor regularly. Realize this will take years to control. Pick a path you can stick with.
    • There is a reason they are called invasive plants. If they have colonized an area, it will take time to remove them.
    • Whatever technique you choose for control, monitor your progress to see if the technique is effective to weaken and reduce them.
    • If invasives have dropped seeds, those seeds can remain viable in the soil for many years.
    • If invasives have extensive roots or rhizomes, it can take years to properly exhaust, smother, or poison them.
  • Consider professional assistance.

Steps we can take

We can all play a role to help reduce the spread of invasive plants, on our property, and the properties we manage or visit. See all of the above guidance. Remove invasive plants. Plant and encourage native plants. Remember that "weed" is a subjective term. Identify the plants in your landscape. Learn about horticulture and the environment.

We can also encourage governments to properly manage public lands and educate the public about this problem.

Steps government can take

Here are some things government can do:

  • Fund education for consumers
  • Encourage proper labeling of plants offered for sale
  • Prohibit sale of invasive plants
  • Require education and training for licensed professionals (arborists, landscape contractors, etc.)
  • Require arborists and landscapers to notify owners of invasive plants on their property
  • Fund remediation of lands dominated by invasives
  • Fund non-profits who work in the field to educate and take action
  • Better manage government lands and right-of-ways that are overgrown by invasives.
    • Government parks and natural spaces are important
    • Governments manage over 4 million miles of roadway and parallel greenspace within the U.S.
      • Imagine clean roadways, free of litter and invasive plants, and full of beautiful native plants.

Conclusion (and disclaimer)

Invasive plants are a threat to our environment, public lands, and private property. Let's be better stewards by learning about invasive plants and controlling them properly.

Hopefully this article helps you learn about invasives faster than I did. If I had started learning about them thirty years ago, my progress would have been much better.

Gardening is my hobby, not my occupation, but I have some practical experience in the field, done a lot of trial and error, and most importantly I have researched what experts have said and written.

Feel free to do your own research from respected and reliable sources, including as listed below.

Of course this is not consulting advice and clearly not legal advice. As always, and in accordance with the terms of use of this website -- and to inject some legalisms into this article -- I assume no liability, and you need to make your own decisions and evaluate your own risks. Herbicides can be dangerous so use at your own risk and in accordance with the label instructions and warnings. Thinking about taking down that invasive Norway Maple tree? Chainsaws are really dangerous, and so is being near a huge tree that will fall to the ground. Some jobs are for professional arborists and professional pesticide applicators.

Additional reading and resources

This article is hosted at https://johnbandler.com/invasive-plants. Copyright John Bandler.

A version of this article is also available on Medium.com, at https://johnbandler.medium.com/invasive-plants-28e7f9547b0a (though perhaps not kept as current, without the references, and not formatted as well).

Originally posted on 2/25/2022. Last updated on 7/8/2024.