|Mimosa tree (Albizia julibrissin),|
a Category I invasive in all of Florida.
Yet, many of these plants are still for sale
How did we get into this situation?
A few hundred years ago, once world travel was readily available, many plants and animals were transported from their native habitats where natural checks and balances evolved over millennia so that predator & food sources were in balance. (I will be talking about plants in this post, but invasive animal species are also a huge problem in Florida.)
People moved thousands of plant species for a number of reasons:
- to bring food crops with them as they settled into new places.
- they collected beautiful plants from around the world to plant in gardens as a novelty or for prestige.
- Some plants were imported for their utility such as stopping erosion (such as kudzu (Pueraria montana)) or building fast-growing hedges (such as, Brazilian pepper (Schinus terebinthifolia)).
- Many non-native plants have been favored in the landscaping industry because most local insects and other critters do not feed on them, so they are easier to grow and sell, because they "look good."
- Sometimes the plants were introduced to new regions by accident as hitchhikers with other plants or with other products that were being transported.
What is "invasive" and how is that status determined?
The vast majority of the non-native plants have not become invasive, but those that have escaped cultivation and have damaged native ecosystems, cause huge problems for Florida. The label of "invasive" for a plant is not lightly given and comes only after years-long study of that plant's behavior in Florida's wild areas, parks, and open lands by scientists working with the Florida Invasive Species Council (FISC).
FISC's working definition of invasive: "A species that (a) is nonnative to a specified geographic area, (b) was introduced by humans (intentionally or unintentionally), and (c) does or can cause environmental or economic harm or harm to humans." (Click here for more Invasive Species Terminology and Definitions.)
Florida Invasive Species Council (FISC)
(formerly Florida Exotic Pest Plant Council (FLEPPC))
The mission is to reduce the impacts of invasive plants in Florida through the exchange of scientific, educational, and technical information.
One of their most important services is to oversee the research on how non-native plants behave in wild areas and to determine which plants are invasive or have the potential to become invasive. Their extensive field work informs the inclusion of plants on the list of Category I or Category II invasives list. "Invasive plants are termed Category I invasives when they are altering native plant communities by displacing native species, changing community structures or ecological functions, or hybridizing with natives. This definition does not rely on the economic severity or geographic range of the problem, but on the documented ecological damage caused. Category II invasive plants have increased in abundance or frequency but have not yet altered Florida plant communities to the extent shown by Category I species. These species may become Category I if ecological damage is demonstrated."
A new list is issued every two years. As of this writing (2021), there are 166 plants that are listed as Category I or Category II invasives in Florida. Click here for the page with the current FISC invasive plant list.
This ongoing study and determination is scientifically rigorous process and is accomplished by botanists and ecologists with years of experience. As gardeners looking at our own yards, we do not have this wider viewpoint of analyzing whole ecosystems like the FISC scientists, so how a plant behaves in our yard or whether or not it is growing in a container is not important in the topic of whether a plant is invasive or not. While many known invasive plants spread aggressively wherever they grow, others seem tame in our yards, but this doesn't anything to do with the problems that they are causing in our wild lands.
Even with all their problems and all the money being spent to remove them, many of these known invasive plants are still for sale in retail garden shops and in the wholesale markets for business and residential developers. A new nationwide study showed that 61% of the known invasives are for sale and unless customer demand is reduced or unless new regulations are put into place to stop these sales, the invasives in wild areas will continue to increase and the money needed to have them removed where they are doing the most damage will also need to be increased.
What about sterile cultivars?
Because invasive plants are so easy to grow and produce and because they are very likely to succeed in people's yards, the growers have developed sterile cultivars that do not produce seeds for some of the invasive plants. For Mexican petunia (Ruellia simplex), 'Purple showers,' 'Mayan Purple,' and 'Mayan White' are sterile cultivars, which means that they don’t develop seeds. These cultivars reduce the spread of seeds, but you can't tell by looking at them whether or not they are the straight species, which is a Category I invasive for all of Florida. And it's quite possible that these cultivars will cross pollinate with the straight species and that may have unintended consequences. I agree with the Jeff Goldbloom character in "Jurassic Park" who warned the managers of the that park that Nature will always find a way to reproduce.
There are also sterile cultivars of some other invasives such as lantana (Lantana strigocamara) and others. While sterile hybrids may cause less damage than the straight species, they still do not play significant roles in the local ecosystem and they could possibly increase the problems and viability of the invasive species by cross-breeding.
My struggles with invasives
|Mexican petunias in the bed next to
and behind the garage.
|Mexican petunias grew right through the weed
There were Mexican petunias in our gardens when we purchased the house in 2004. They grew right through the weed barrier cloth that the former owners had laid down with volcanic gravel on top. It took several years to remove them all from these beds because the tiniest bit of root created a new plant. Meanwhile, it had spread to the edge of the pond out front and I'm still finding it and removing it from there more than a decade later. What a pain!
|Harvesting water hyacinth
from the lake.
|An area where I removed wedelia from a bank near the lake.
Our lot backs up to the end of a finger of the eastern shore of a lake. (For orientation: the locations of two photos above are close together. Over my right shoulder as I'm standing in the water is the dock you can see in the other photo where I'd cleared out the wedelia.) The prevailing winds means that stuff that floats ends up in the end of our finger. This includes trash, inflatable toys, and the floating water hyacinth (Eichhornia crassipes), a Category I invasive in Florida. A large portion of the $54 million spent in Florida are to clear this and other invasive waterweeds from our waterways so that boat traffic can flow. There is a cottage industry associated with the removal of this invasive making fertilizer because the plant is so nutrient-rich. I use to gather these plants and use them for building compost, either in piles or for composting in place. This doesn't happen much any more because the lake has been treated with herbicides.
For the most part I have removed the wedelia (Sphagneticola trilobata) from our yard, but it makes its way back in because neighbors on both sides of us have allowed this attractive invasive to grow in their yards. It's quick to take over. Read Winter: a good time to remove invasive plants, which relates my unfortunate adventures with wedelia. While it's only on the Category II list of Florida invasives, it has been a huge and ongoing problem in our yard, but it's still commonly sold.
|Nandina or heavenly bamboo |
Heavenly bamboo (Nandina domestica) is a Category I invasive in all of Florida and in many other states as well. Birds eat the berries and poop them out in wild spaces with a dollop of fertilizer.
That is bad enough, but migrating birds that come through our areas gorge on berries to fuel up for the next leg of their migration and these birds, such as the Cedar Waxwings have been poisoned by the nandina berries, which contain cyanide and other alkaloids that produce highly toxic hydrogen cyanide (HCN).
Yet, this shrub is still for sale. I did point this out to the Clay County Delegation two years ago when I brought a nandina plant to the meeting that I'd bought that morning to drive home the point. No legislation has been passed. I will try again to get their attention that these should not be sold when they are doing so much harm.
Here's the article on the bird poisoning: Nandina Berries Kill Birds: Popular garden shrub berries are toxic to birds and other animals.
We need to talk more about invasive plants for many reasons
|Native plants play important roles in the|
local ecosystem. Join and support your
local FNPS chapter.
I decided to put this post together so that all the arguments and references for why invasive plants are such a bad idea would be in one easily referenced page. It is my opinion that most gardeners are good people who are friends of the earth and want to promote earth-friendly practices. I share this information so that people will know more about what is invasive in Florida and why invasives are so harmful. And my hope is that some people will change their behavior and speak up when they see invasives for sale and maybe even speak up to their elected representatives to convince them that known invasives should not be sold. Money can be saved is the key argument. $54 million is a bunch of money and as things stand right now, the situation will only get worse if the sales are not outlawed.
But, in the end, why not plant Florida natives when you have the chance? Thanks for doing your part in making native plant landscapes the new normal in Florida.
Green Gardening Matters,
For further reference:
- Details on money spent to deal with invasive plants in Florida from Conservation Science and Practice: "Allocation of invasive plant management expenditures for conservation: Lessons from Florida, USA"
- A new study shows that 61% of invasive plants are still available in the retail trade nationwide: Invasive Plants Still Widely Offered for Sale in US
- I wrote this article for the FNPS blog in 2011. It's still receiving heated comments. Australian Pine: One of Florida's Least Wanted
- Invasive vs. Aggressive: They are not the same, an article that I wrote for the FNPS blog with links to multiple additional articles on this topic.
- Removing Invasive Plants, an article with references from IFAS Extension Service.
- Why are invasive species a problem? by U.S. Fish and Wildlife Service.