What’s Wrong with Non Native Plants?

 

I get this question a lot. Mostly people are asking the question in regards to using non native plants in their garden (non native plants naturalizing into wild spaces is a different question not covered here). When shopping for plants, the availability of non native plants vastly outpaces the selection of native plants so choosing native landscape plants requires more time and effort.

People like to point out that the plants they are buying/using have flowers that the bees and butterflies can use, birds can make nests in the plants just as well, and of course the plants tick off all the usual reasons for landscaping: they are green, they look good, they can be shaped/controlled for size, and they illustrate that someone lives there and cares for their yard.  So when I make recommendations for specifically seeking out and using native plants INSTEAD, the questions come back: “What’s wrong with using non native plants? What do they do wrong? They are not spreading anywhere.”

The answer centers not as much on the point of what is wrong with what they do; they obviously “do” a lot for the conventional landscape (again, they’re green, they’re pretty, and they are available in all the stores). The answer centers on what they don’t do.

Luna moth - born and raised on native trees

Plants that have evolved with the insects in their ecoregion – that is native plants – have become part of the ecosystem that needs its components to thrive. Two points in particular should be considered:

1.      Host plants: Certain insects such as butterflies and moths (Lepidoptera) are herbivores, requiring certain plants on which to feed. The Monarch butterfly and its relationship with milkweed (Asclepias sp. plants) provides a well-known example. If a female Monarch cannot find a milkweed relative, she cannot lay any eggs for the next generation. If we want butterflies (and moths), we must plan for them and choose the right plants. Plants from other parts of the world did not evolve with our insects (although, in a few small cases like parsley/dill/fennel they might be close enough relatives of our native plants for butterflies like the Eastern Black Swallowtail but that is the exception).

2.      Specialized pollinators: Much like some insect herbivores rely on certain plants to raise their young, some pollinators have evolved to be specialists. My favorite example is the Southeastern blueberry bee (and there are many other specialist bees).

Zebra swallowtail - depends on paw paw (Asimina)

Southeastern blueberry bee on blueberry (Vaccinium)

While not all insects are specialists, having adapting to use more than one type of plant for eggs or able to use several types of flowers, what is true is that native insects get the most out of native plants. The large and beautiful Luna moth lays her eggs on native trees like sweet gum, hickory, and walnut. Popular non native landscape trees like crape myrtle, ornamental cherries/pears, Japanese maples and shrubs like butterfly bush, loropetalum, privet/ligustrum and gardenia don’t support insect herbivores in any sustainable way (if at all).

Oakworm caterpillars - one of the few to eat in a group

Most caterpillars are solitary and hardly noticed

You might think that not having insects nibble on your plants is a good thing, but balance that with fewer butterflies and moths to enjoy or to support birds. The vast majority of caterpillars do not defoliate plants; if you have oak trees in your yard, chances are they are supporting caterpillars and you didn’t even notice because they prefer the top leaves.

Birds want your caterpillars! Photo: Romin Dawson

So to go back to the original question, the ecological answer to ‘what’s wrong with non native plants’ is that there isn’t enough right with them to support our insects. If you’d like to contribute to the place you live in a way that supports the ecosystem, include more native plants in your design. It’s not hard to do thanks to an increase in demand for native plants and an increase in the amount of education out there. In Georgia, here is a list of nurseries that carry large and small amounts of native plants