A question often asked when giving presentations on landscaping and sustainability "Are native plants better than non-natives?"
In my garden, I avoid holding myself to an exclusive natives-only approach, and other gardeners do not have to either. My process for choosing plant material and ruling out species is always to ask if the plant is considered aggressive or invasive. Often 'aggressive' and 'invasive' are used interchangeably, but invasive is a legal term. Invasive plants are those that cause economic, human, or environmental harm. The state of Illinois identifies plants that are deemed invasive through the Illinois Exotic Weed Act. Aggressive plants are simply garden thugs that spread throughout landscape beds and are difficult to control.
There are plants sold in garden centers that are not legally termed invasive, but we have seen them escape cultivation and start to crowd out vegetation in natural areas. Burning bush (Euonymus alatus) and ornamental pear (Pyrus calleryana), two plants commonly sold at garden centers, are becoming a problem in West-Central Illinois. These aggressive plants are species of concern and have all the characteristics of a legally invasive species. These plants (and a handful of others) are crossed off my list.
Non-native plants that can grow well in your area, without excessive inputs, and will not escape into natural areas are termed adapted plants. There is nothing wrong with mixing native plants with plants adapted to your site. In fact, that is likely what can make your garden so dynamic and unique while still being part of a local identity and ecology.
An example of an adapted plant is Gingko biloba, a tree rediscovered in Asia, making it a non-native plant in the US. Gingko is very well adapted and tolerant of all types of urban soils and pollution. Moreover, it has wonderful yellow fall color, and the leaf shape is dramatic all in itself. However, unlike an oak tree, gingko does not support a vibrant natural community. Almost nothing in North America feeds on it, therefore making it a very poor contributor to local food webs. Do not discount gingko just yet! Gingko still has value for its ability to withstand a myriad of conditions without escaping and becoming invasive. Plus, though its growth and natural plant processes, gingko does help to sequester carbon, filter runoff, and reduce erosion. All splendid traits.
Native plants are still going to be the best option for gardeners wishing to take a sustainable approach. For property owners in Central Illinois, tallgrass prairie forbs and grasses are well-suited for our climate. Understory plants could include dogwoods (Cornus sp.) and redbuds (Cercis canadensis). Evergreens such as eastern red cedar (Juniperus virginiana) provide great cover for wildlife in the winter. Canopy trees such as oak (Quercus sp.), hickory (Carya sp.), and walnut (Juglans sp.) are desirable for their shade and wildlife contributions.
If you wish to promote wildlife habitat, do your research. Butterfly bush (Buddleja davidii) is a great nectar source for butterflies, but it is native to Asia and not a host for butterfly caterpillars. A better option would be milkweed (Asclepias sp.) which is a host to monarch butterfly and nectar source for adult monarchs and various other nectar feeders.It's tough to give plant recommendations on such a broad scale, native or otherwise. My advice for readers is to contact your local Extension office for a list of plants that are native or adapted to your region.