London plane tree. (Credit: Pixabay)

In recent years, environmentalists as well as many gardening enthusiasts have placed a great amount of emphasis on the use of native plants in the landscape. Their rationale assumes that native species often require fewer inputs in the form of water, fertilizer and pesticides. Unfortunately, this has led many people to disparage the use of non-native plants, regarding them as undesirable occupants of our created landscapes. The stance "if it's not native, don't plant it" seems to be gaining popularity in the gardening world. While not wanting to discourage individuals from planting native species, this article seeks to defend the responsible use of non-natives in the landscape.

Forsythia, a harbinger of spring in the Midwest, is native to China and Korea. (Credit: Pixabay)

Non-native plants are those that originated elsewhere and would not be in the United States were it not for human intervention. Also called exotic species, non-native plants can be placed into one of two categories: acclimatized and adventive.

Non-natives that have changed in order to adjust to their new environment are said to have acclimatized to an area. These plants do not need human help to reproduce and maintain themselves over time in an area where they have been introduced. The term "naturalized" often is applied to plants of this type of plant, which includes some of our important food species.

Apple is an example on a non-native species that has acclimatized quite well to the United States. (Credit: Pixabay)

In contrast, adventive non-natives differ from naturalized species in that they do not have the reproductive ability to establish themselves long-term in the environment over vast areas. However, a constant renewal of individuals by humans can sustain an adventive population. In short, adventive non-native plants do not naturalize.

There are several reasons that can be cited to support the use of non-native plants. They include:

• Aesthetic appeal: Non-native plants can introduce vibrant colors and textures that may not be found in native options, thus enhancing the beauty of landscapes.
• Disease resistance: Since they tend to be genetically isolated, some non-native plants may be more resistant to native diseases and pests, leading to healthier and more vibrant gardens.
• Drought tolerance: In arid, drought-stricken regions, certain non-native plants can be more drought-tolerant, requiring less water than native species.
• Increased biodiversity: While often a concern, some non-native plants can contribute to overall biodiversity, particularly in urban areas where native ecosystems already are modified.
• Food and other resources for wildlife: Non-native plants can provide food sources or nesting sites for certain native wildlife species. Pollinators benefit from non-natives which flower at times of the year when little else is in bloom.

• Culturally significant plants: Non-native plants may have cultural or culinary significance, offering a connection to different regions and traditions.
• Enhanced landscape beauty: Non-native plants can create a "wow factor" with their unique features and can add visual interest to a landscape.
  
  

  Dahlia is an example of a non-native with vibrant color and "wow factor" not found in many native species. (Credit: Pixabay)

The late author and naturalist Jim Anderson made the following points about planting non-native plant species:

• Invasive pests are less likely to kill non-native plants. Since non-native plants lack established interactions with native insects, they are less appealing or suitable as a food source for many native insect species.
• Some non-native plants are genetically isolated rendering them more pest resistant. Many pests have developed mechanisms to overcome the defenses of their native host plants, Non-native plants, on the other hand, lack this coevolutionary history with local pests, often making them more resistant.
• Non-natives may be adapted to environmental extremes more so than natives. The ability on non-native to adapt to environmental extreme can be due to faster growth rates, more efficient seed dispersal, and a broader tolerance for different environmental conditions.
• Non-natives can support biodiversity. Some non-native plants, particularly those that are not invasive, can provide food and habitat for native insects and wildlife, potentially increasing local biodiversity.
• Pollinators can love the pollen and nectar of non-natives also. Renowned horticulturist and author Dr. Allan Armitage is quoted as saying, "I also have heard the myth that all native pollinators are attracted only to native flowers. Hogwash! Many herbs and annuals, although not native, are very good for pollinators."
  
  

  Butterfly bush is a favorite of many pollinator species and has an extended bloom period not found in many native species. (Credit: Pixabay)

• Some non-native plants flower at times of the year when little else is in bloom. As an example, butterfly bush (Buddleia davidii) blooms throughout the summer and into the fall. This long period of flowering can overlap with some native blooming plants but also extend beyond the typical flowering season of many native species.

London plane tree (Platanus × hispanica) provides a good example of the judicious use of a non-native species. Numbering more than 80,000, it is the most widely planted tree in New York City. Introduced from Europe in the 17th century, it is highly tolerant of pollution and compacted soil, making it well-suited for city streets and parks. Additionally, it is low maintenance with few disease problems. Many would contend that it outperforms American sycamore (Platanus occidentalis), its closest native relative.

Unfortunately, the use of native vs. non-native plants has become somewhat of a moral issue, with strong opinions on both sides. Proponents argue that prioritizing native plants is imperative to protect biodiversity and ecosystems. In opposition, critics argue that focusing on native plants can be a form of plant "speciesism." The latter holds the potential of overlooking the freedom to cultivate diverse landscapes and the practical need for adaptable plants in changing environments.

'Tricolor' European beech, when properly grown, is one of the most striking landscape trees that can be found. (Credit: Missouri Botanical Gardens)

The bottom line is plant what works for you. Truly invasive or noxious species should be avoided. The Missouri Department of Conservation maintains a list of these species (https://mdc.mo.gov/trees-plants/invasive-plants). Take time to learn more about the species that appeal to you, be they native or non-native. Avoid giving undue deference to a plant just because it is native. Not all native plants are good, nor are all non-native plants bad. The priority should be to select plants that are well-suited to site conditions, support local wildlife, and contribute to overall ecosystem health.