Like most issues, there isn’t a simple answer to the question of what we should plant. I’ve spent over 30 years working to protect natural communities and rare native plants in their native habitats as well as in cultivation and my own opinions have constantly grown and evolved over the years. My best advice to have a positive impact with your garden is to plant for environmental/ecological services and that can only be done by knowing the benefits of each plant we are planting.
We feel that a plant’s environmental service is far more important to the world than its current range. In this day when pollinator populations and insect populations are crashing around the globe the support of native pollinators and insects is our top concern. Planting a garden with species that support these insects is probably a much greater ecological benefit than simply planting something that grows at this point in time in your neighborhood.
There are also issues with masses of “native” plants swamping the genetics of local species. As an example, Echinacea are known for hybridizing and though native plant societies frequently promote planting Echinacea purpurea, E. pallida, E. paradoxa, or E. tenneseensis – these plants aren’t locally native here in the Piedmont of the Carolinas. If a population of Echinacea laevigata, which is federally threatened, is nearby, the genes of the more commonly cultivated “native” Echinacea can be transferred to the threatened species resulting in hybridization that destroys the genetic integrity of the population.
Just because a plant isn’t invading now doesn’t mean it won’t be a problem in the future. As gardeners, we all must pay close attention to the attributes of our plants to observe their ability to expand outside of the garden setting. If we see a plant seeding away from our managed space into natural communities, we generally delete it immediately from the landscape. Many plants considered to be “native” are just as capable of expanding and changing native ecosystems as non-native plants. A good example can be found in Prunus caroliniana – Carolina cherry laurel. This is a beautiful, evergreen that makes a wonderful small landscape tree, but when planted away from its native haunts in the coastal plain very quickly starts to take over wood lots and push out other plants. It is native to the Carolinas but also has the ability to leap well-beyond its local range.
As you can see, the issue of “native vs. non-native vs. invasive” is quite complex and made even more difficult by the issues we see with a rapidly changing climate and limitations that are placed on our resources such as water. Though native plants are often billed as not needing water, nothing could be farther from the truth. They are every bit as hungry for water as plants not native to the Carolinas. To keep them looking beautiful we must supplement their water budget.
There are plants known as “near natives” that hail from places like the Chihuahuan Desert of Texas or the Edwards Plateau that provide the opportunity to plant close relatives to native plants that often support the same insect larvae and pollinators as their locally native counterparts but can do so on a highly reduced amount of supplemental water. Sometimes amazing pollinator plants like Rattlesnake Master (Eryngium yuccifolium) that are often considered only marginally beautiful can be replaced by showier species such as Ravenel’s Eryngo (Eryngium ravenelii) which are extraordinarily beautiful and support just as many, and the same, pollinators. The Ravenel’s Eryngo is native to NC and SC but in the coastal plain. If we really wanted to maximize the space for pollinators, we might choose Eryngium pandanifolium – from South America, and though not locally native it produces a much, much larger spray of flowers that draw in and benefit the same insects. The native wasps, flies, sweat bees and bees that are foraging on this plant don’t care that it’s from South America any more than we should care that a pineapple is native to South America before we eat it.
Like I stated earlier, there isn’t a simple answer to the question of what we should plant, but I hope this has answered some questions and raised some questions to foster continued discussions of our impact on environmental and ecological systems.