For our third and final part of the discussion on native plants and exotic plants, it seems like we need to get to the heart of the matter. You need to choose a plant to add to your garden, so are you planting a local native species or an exotic species?
Now, if you’ve read the first two episodes of this series, you already know the answer to that question — it depends!
So for this entry, I turned, of course, to the guardian of all knowledge…the Internet. I mean, who needs rigorously tested hypotheses and impeccably presented discussions of research findings when I have easy access to online musings from Kim Kardashian, Snoop Dogg, and “Weird Al” Yankovic?
My research online yielded a list of comments that I thought I presented as a True/False test.
So here are six true or false questions about whether you should plant a local native or exotic plant species in your garden. Let’s see how you do.
Natives are best planted as they are best suited to local growing conditions
It’s interesting. To approach this one, think of our old friend the Honeysuckle of Love (Lonicera maackii). Clearly an Exotic and obviously a wildly invasive Exotic. We have already covered how it moves through both woods and fields in many parts of the eastern United States and chokes out just about anything in its path.
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I’m not sure about you but to me it seems that the Amur honeysuckle is much better adapted to the growing conditions than the natives that are left in the dust. Does that mean we should run out and replace all our native plants with honeysuckles?
Of course not. But the thing about “native plants because they’re better locally adapted”…this dog just doesn’t hunt.
In general, native plants are more in tune with local pollinators because they evolve together
The poster child for this one is the now well-documented myth that many tropical orchids are pollinated by a single species of insect. It is certainly true that some plants are successfully pollinated by a wide range of general pollinators, but there are others that have a much shorter list.
But only one species? Not really. In general, ecological factors such as reaction to changes in temperature profiles, changes in day length across seasons, and others seem to give the nod to local plant/pollinator pairings as being generally more synchronized. . Undoubtedly, there are many well-bred exotic plants that pair quite well with local pollinator species. It’s a mixed bag but in general we’ll give the nod to Indigenous partnerships.
All exotic plants are invasive because they are free from the pests, diseases, and herbivores they face in their native country.
In the high plateau of Tibet, there is a plant that grows in the high alpine meadows. Stellara chamaejasme (it doesn’t even have a common name), is a plant that could very well have me selling my soul to the evil gods of horticulture just for the chance to successfully grow a single specimen.
I tried. I tried. I tried.
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It is an amazing plant with a scent that makes you weak in the knees and stays that way for good. I know of a plantation in North America in the city of Denver, Colorado. I have visited it several times.
Do you see where I’m coming from? Not only is this stunningly beautiful, exotic cell-walled mermaid non-invasive, it is also virtually impossible to grow in most places on the planet other than high mountain environments, let alone my garden in Louisville. , Kentucky. Of course, that’s an extreme example, but I think you get my point. “Exotic” and “invasive” are not synonymous.
In fact, despite the fairly obvious handful of seriously bad actors, the vast majority of introduced/exotic plant species are plants that do reasonably well in the garden.
Native plants are better because they have deeper root systems and can cope with occasional droughts
There’s a graphic floating around the internet that’s been appearing in PowerPoint presentations at garden conferences for years. It shows the supposed profile of a group of native and exotic plant species with drawings of their tops and bottoms (roots). And quite magically, it clearly shows the exotics with extensive and very shallow root systems and the natives with deep carrot-like roots.
The problem is that it is completely manufactured! Of course, you can select a few deep-rooted native species and a few shallow-rooted exotics. But overall, the root system architecture is a very complex product of millennia of evolution. Even in the same ecosystem, you can find local native plants growing side by side with completely different root system profiles.
Indeed, plant communities evolve together to really exploit all available space and resources. If all the plants in an ecosystem developed the exact same rooting strategy – or pollinator attraction strategy, or any other adaptation for that matter – it would be a rather weak community with very low resilience.
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Introducing non-native genes into an ecosystem can damage fragile native plant species
This is a difficult question.
Short’s Goldenrod (Solidago shortii) is a local endemic represented in the wild by only a handful of very small populations. It is an attractive small summer bloomer found in open meadows and edges of woods. The problem is that many of these small isolated populations are so small and have been effectively isolated from each other for so long that they exhibit what we call inbreeding depression.
Due to too shallow a gene pool, some of these small goldenrod populations produce few or no viable seeds.
So here’s the catch. Are we artificially introducing plants from one population to another population to add a deeper end to the gene pool and give populations a genetic boost? Is this our place in the grand order of nature? Should we do everything we can to keep these small, unique populations completely isolated and watch them march towards inevitable extinction?
The whole discussion about maintaining genetic purity is vast and complex. I am simply presenting the story of our little goldenrod as just one example to illustrate how complex it can be.
RESULTS: Neither (it’s complicated)
Do not plant English ivy and creeping euonymus as they are invasive alien species
There is little argument as to whether these two popular landscape plants are a problem or not. Granted, they are exotic and no doubt they are invasive in and around Kentucky. But here is the question. With what appears to be two by three meters sporting a version of one or both of these species, and with the two unleashed in parks and wilderness areas across the country, let’s make matters worse by planting two more plants around the mailbox?
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Personally, I wouldn’t have any in my garden either. Not only are they ecologically destructive, but they are also ridiculously vigorous plants that want to take over your entire garden. For me, the question is not so much whether or not these are invasive alien species. For me, I won’t have either of these in my garden because they are a pain. They are weeds. There are so many better garden plants.
AT Yew Dell Botanical Gardens, we have adopted the philosophy that we seek and promote what we call “Good Garden Citizen” plants. If they’re invasive, we don’t grow them. We don’t want to add to the problem of invasive plants. But if a plant is weedy, overly aggressive, or makes gardening more difficult, we’re not interested in whether the species is native or exotic. Avoid planting it.
Canadian Goldenrod (Solidago canadensislisten)) is native to much of North America. It is a small, hardy native prairie plant that blooms in late summer and serves all manner of pollinators. But it is a formidable garden plant because it is much too vigorous and aggressive in a cultivated environment. Of course, it’s native. But on this one, I’ll take a pass.
RESULTS: you will have to answer this one by yourself
Paul Cappiello is the executive director of Yew Dell Botanical Gardens, 6220 Old Lagrange Road, yewdellgardens.org.