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 where I do my gardening and observe nature and plants on a daily basis. 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 can improve our future, and 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 extremely 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 ideal conditions and 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.

"Weed" is a 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, and human opinion is not always correct.

An invasive plant is always harmful, and thus should always be considered a "weed" and managed.

Invasive plants get the designation from scientists after careful evaluation of their impact on the environment. Every invasive plant is 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.

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 what they need. Private lands and public lands degraded. It does not need to be this way.

Examples of invasive plants

There are invasive plants in every region and state, my experience is with the New York and Connecticut area, you should familiarize yourself with what is invasive in your region.

Having learned about them on properties I visit and maintain, I now realize they are everywhere: along roadways, on public lands, on private property.

One more mention about terminology. 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 (thanks to science). To fight an invasive weed we want to properly identify it including both common names and scientific names.

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.

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, good military planning concepts suggest having a sound strategy for the long term and good tactics for short term operations.

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 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.
      • I think my guidance is reasonable and backed by science an reason, but see what the experts say (links below).
  • 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 with 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)
    • 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 this can be difficult or impossible to achieve that immediately.
    • Weakening the plants is a first step. This can reduce its propagation, spread, and dominance over neighboring plants.
    • Avoid digging. Digging is problematic because of the potential to bring seeds to the surface for germination, and to 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, whose 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 and smothering a fifty foot tree. Cutting the vine at the base robs the invasive plant of all the future 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 vine will live, but greatly weakened.
      • Some say cut the vine and paint the cut with herbicide, which can kill the vine. 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.
    • 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.
      • 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, whereas hand-pulling has proved ineffective over the years.
  • 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. We can also encourage governments to properly manage our public lands, and educate the public about this problem.

Steps government can take

Here are some things government can do:

  • Fund education for consumers
  • Require education and training for licensed professionals (arborists, landscape contractors, etc.)
  • Require arborists and landscapers to notify owners of invasive plants on their property
  • Prohibit sale of invasive plants
  • Fund remediation of lands dominated by invasives
  • Fund non-profits who work in the field to educate and take action.

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 helped you to learn more faster about invasives than I did (e.g. it took me thirty years). Gardening is my hobby, not my occupation, but I have some experience in the field and I have researched from the experts. 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.

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 8/3/2022.