Tuesday, January 18, 2011

Native Plant Myth #2: Native Plants are Not as Tough as Exotic Plants

Few issues in the gardening world generate as much heat as the debate about native plants.  As a result, native plants have developed their own dogma.  It’s that dogma that I want to set straight.  So I’m here to bust some of the top myths about native plants.  Let the smackdown continue:
Myth 2: Native plants are not as tough as exotic plants. 
This is one I hear all the time among landscape architects.  “This site is too brutal for natives,” a colleague said recently.  He was referring to an urban parking lot that would not be irrigated.  Implicit in the assumption is the belief that natives are somehow weaker and more delicate than exotics plants. 
Wild some natives like trillium
may not be tough enough
for urban areas, others are.
It’s easy to understand where this mythology comes from.  A forest of mostly native species gets razed for an office park.  The client expresses a desire to use mostly natives on the new site, perhaps as a way to mitigate the fact that an energy-sucking office park just ate a forest.  But the conditions have changed now.  The precious native ephemerals such as tiarellas, trilliums, and geraniums that thrived under the cool woodland canopy will no longer survive on the edge of a sunny parking lot, especially once the maintenance crew salts it in winter.  So the designer reverts to a “tried and true” palette of juniper, berberis, and euonymous to green the parking islands.
This line of thinking is not limited to designers.  Senior research scientist of the Arnold Arboretum, Peter Del Tredici wrote, “My advice is simple: don’t limit your planting designs to a palette of native species that might once have grown on the site. Imposing such a limitation on diversity not only reduces the aesthetic possibilities for the landscape, but also its overall adaptability.” 
The assumption made in both cases is that the only native plants appropriate for the site are those that used to be there hundreds of years ago.  If you leave anywhere east of the Mississippi, that probably means some kind of woodland.  Of course, many of these plants would be poorly suited to harsh urbanized conditions.  But what about native plants adapted to harsh conditions?

Native vegetation on harsh urban-like conditions of granite outcrops in Heggie's Rock in Georgia.  Painting by Philip Juras.

I remember hiking through some of Georgia’s granite rock outcrops and marveling at the ability of native plants to live in utterly desolate conditions.  Beautiful patterns of mosses, grasses, and cedars grew in the slimmest pockets of anaerobic soil.  These plants withstood blazing heat, drought, periodic inundations, and infertile soil, and deep frosts— conditions remarkably similar to urban environments.   And it’s not just granite outcrops.  All over the country, native plants thrive in horrifically inhospitable environments.   When we limit our understanding of native plants to a few precious woodland floor plants, we lose sight of their potential in human disturbed landscapes. 
This summer I interviewed Mark Simmons, a research ecologist with the Lady Bird Johnson Wildflower Center.  Mark and his colleagues have done a slate of new research that challenges the assumption that native plants are somehow weaker than exotics.  Simmons has a revolutionary vision of what urban spaces can be: a place where native plants and ecosystems provide ecological services for humans such as stormwater management, pollution filtration, and habitat creation.  “Native plants, as we’re finding, are a hugely untapped resource,” says Simmons. 
This vision is backed with cutting-edge research.  In 2008 Simmons completed a study that compared the performance of different types of green roofs.  Simmons compared 24 different experimental rooftops.  The study showed that green roofs with native plants outperformed green roofs with mostly sedums.  The native plants captured stormwater and cooled the surfaces better than exotic sedums. 
A second study compared the performance of exotic versus native turfgrasses.  Early research demonstrates that the lawns composed of a mix of native grasses outperformed the non-native lawn.  The native lawn better conserves water, resists disease, and handles foot traffic than the non-native lawn.  In addition, the native lawns were indistinguishable in appearance from the non-native lawn.  

Test plots of native
 turfgrass outperform
exotic species.

Simmons’ research shatters stereotypes of natives as weak, underperforming plants.  For example, the Texas Department of Transportation was initially hesitant to substitute native grass seeding for the more tried and true exotic Bermuda grass.  Simmons tested a way to artificially increase the density of native wildflowers.  Not only did the native grasses and wildflowers grow better, but they also reduced populations of the invasive bastard cabbage which grew alongside the Bermuda grass.
Simmons is optimisitc about future applicaitons of native ecosystems in urban environments: "Native ecosystems have the potential to improve almost any urban environmental problem."


  1. Huh. Well, that's a new one to me. I've heard all kinds of reasons why natives shouldn't be used and 'not tough enough' isn't one of them. Maybe it's because I talk to gardeners more than LAs about them.

    And thanks for the link to the green roof study. I'd mostly been told that native bunchgrasses don't work on green roofs because their fibrous root systems want to go too deeply and that sedums are better able to handle the thin growing medium. But the grassland planted on top of the LDS convention center in SLC seems to be thriving, so there's another urban legend shot down.

  2. I don't usually hear the idea that natives are too weak to work in tough landscapes; the misinformation rattling around here in New England is that natives don't need maintenance and don't need irrigation.

    This line was used in every single workshop in a series of workshops devoted to native plants three years ago at Build Boston, the annual trade show for architects, LAs, engineers, and contractors. The series had been coordinated by the LA staff of a very large engineering firm, and it seemed to a number of us in the audience that it was a way to pitch comforting ideas to developers who might hire that firm...Unfortunately, it left the unrealistic impression with prospective clients that native plants can thrive anywhere, no matter their provenance or required site conditions. Your earlier post addressed that topic nicely...

  3. Great post!

    To further support your point, a great way to select plants for a tough site is to identify native plant community that flourishes under similar environmental conditions in your region.

    Trees that grow in flood plains tend to be well adapted to city streets, for example, where they contend with similar extremes of inundation and desiccation, mineral deposition, and physical disturbance. Coastal plants cope well with sun and salt, so some of them may be well adapted to parking lots, as long as the soils drain freely.

    These aren't ironclad rules or formulas; every plant in a given environment has its own adaptive strategy, and every parking lot has its own growing conditions. Although it would be great to reassemble naturally occurring associations, you may end up bring together plants that rarely, if ever, meet in nature. But every region of North America includes tough environments, and the plants that survive there - especially the successional pioneers - are going to be just as rugged as any exotic.

    One last small thought: I question Del Tredici's conclusions, but his book includes some tough natives among the exotics. So if you're looking for urban-hardy native plants, it's another useful place to start.

    Thanks for the opportunity to chime in!

    - Toby Wolf (www.tobiaswolflandscape.com)

  4. Great post! While I agree that native plants can survive in stressful environments (alvars etc.). There is a big difference between these ecosystems and the urban environment...disturbance. Generally speaking plants that have adapted to grow in highly stressful conditions cannot handle disturbance (traffic etc.). That is not to say that there are no native plants that can handle disturbance, they just may not be the ones that grow on granite rocks.

  5. Wonderful post as always. I noticed the following sentence is a part of Monrovia's "Care information": "Follow a regular watering schedule during the first growing season to establish a deep, extensive root system. Watering can be reduced after establishment."

    I like it; there's more sophistication to watering than that, but it goes a long way beyond what I usually hear from nursery personnel.

  6. Yeah, I hear that in the profession, too: that natives are not quite as tough as juniper or berberis or some other overused plant. Simmons research is great. I wish people like him and Tallamy keep up the great research about the benefits of natives. It has changed my mind about using them.

  7. Relevant post, even better than your last!

    BTW, there ARE green industry folks who DO say and imply "native plants are not as tough as exotic plants" in urban settings. This includes one of our own, "noted author, award-winning designer and activist, etc", known by many as a native plant "expert".

    Fortunately, others know better and know how to apply what is in nature. Including laypersons.

    I 1st use local natives from similar sites and are low water-use, then plug in non-native adapted plants where natives don't provide a given effect.

    I sum up both of your posts like this - be intuitive and observant - use natives growing in analogous habitats, micro-environments, etc as your site.

  8. It seems to me that the real point of this and your previous post is more basic than the native v. nonnative issue. Every plant planted anywhere be it parking lot or woodland should be carefully researched to find out the growing conditions it prefers and how they relate to the proposed site. A designer/architect who grabs cardinal flower and puts it in a parking lot because it is a 'tough native' is just not doing his or her job. One look at its native habitat would let them know it's the wrong plant. But this would be the same for a nonnative plant. The real point about natives is that we need to plant native plants as Doug Tallamy so eloquently explains and that there are native plants suitable for all types of growing conditions if you take the time to do your research.

  9. Thanks for this post. And for the green roof link, since I'm involved in a trial green roof project in rural Illinois right now.

    To me, there has always been a difference between knowing plants and where they'll grow (the plants person's perspective) and the typical hort industry perspective, in which plants are part of a business model, products to be produced and shipped, in which standardization and uniformity are prized.


  10. Thomas, excellent blog! I concur with you and have been pushing for this exact paradigm shift among landscapers, nurseries, municipalities, builders and developers, as well. All plants are drought-tolerant in the right conditions. I just created for the SJRWMD a searchable online data base of 800+ (natives and non-natives) plants, shrubs, and trees that cites correct placement based on surviving on natural rainfall after establishment with BMP's. http://publicserver2.sjrwmd.com/waterwise/search.jsp

    It is the most natural way to landscape that conserves water. Installing landscapes (natives or non-natives) that demand irrigation on a regular basis vs establishing a landscape that only needs supplemental irrigation during droughts is a passe' trend. Certification checklists that cite how much water a plant uses based on ET without taking into consideration the soil conditions, humidity, and ensuring proper maintenance after installation will probably never be water conserving.

    Check out my New Year's post on Old Landscaping Trends Of The 20th Century And My Solutions For 2011.


    Definitely adding you to my must read blog list!

  11. Recently learned about the research on natives versus mainstream/assumed best options from Thomas - I had previously done some research on LadyBird Johnson Center - and was so impressed by the stated purpose of that center - so their recent testing on natives outperforming exotics - was wonderful to learn.
    More "education" (or call it marketing) of the general public and our government officials is needed. We've got to re-define and re-shape what is optimal and beautiful, to appreciate the genetic diversity. It's not just about plants and their well-being, it's also about the animals and insects and yes, people who depend on the genetics of the natives.

  12. I lived in the Texas Hill country, and my garden was either solid limestone or highly alkaline. I used only native plants and had great success creating a beautiful garden that was sustainable. I don't believe anything else would have been as successful. I think this is true for most places, as long as the plants are sited carefully.


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