NATIVE PLANTS IN THE LANDSCAPE

by Al Cooke
Agricultural Extension Agent
Chatham County Center
North Carolina Cooperative Extension Service

The term "native plants" conjures up many images. There is a popular belief that if we limit ourselves to native plants then we will have virtually trouble free gardens. Among the myths associated with native plants: "Native plants are more aggressive and better adapted." If this were true, then we would not have any of the problems we have come to associate with “invasive plants.” Is any plant more aggressive and better adapted than Japanese kudzu or Japanese stiltgrass? "Native plants are disease resistant." The American elm and American chestnut were essentially eradicated from their native ranges by diseases. These were trees that once dominated our eastern forests. We have not restored them because we still cannot cure the diseases that took them away. "Native plants are insect resistant." The native flowering dogwood is overwhelmingly plagued by borers. The problem seems less serious among wild trees not planted by urban gardeners. One might legitimately wonder if our appropriation of this native plant has worsened its plight. "Native plants are more drought tolerant." Native plants include aquatic plants, bog plants, and wetland plants. These plants may or may not have mechanisms for surviving short- or long-term water deficiency. Insufficient water almost always places a plant under some stress. And stress makes plants more susceptible to disease and insect pests. "Since native plants grow wild, little site preparation is necessary." A native plant that produces hundreds of seeds can count itself a botanical success if only one of those seeds grows to a mature plant. Gardeners may have higher expectations. Actually the concept of native plants is a human concept that bears little on the ability of a plant to thrive. By asking whether a plant is native we automatically assume native to a continent, a region, a state, a county, an ecological niche, a soil type, or some other definition of space. Plants have existed in these spaces for longer than humans have been present. In the age of plants, continents have been separated, moved, and rejoined carrying plants with them. The beginning of agriculture by humans is synonymous with the beginning of civilization. Humans began to grow plants in areas where they wanted them, sometimes but not always successfully. We had our own impacts on where plants would grow. But plants have not been limited to using humans to increase their geographic range. Plants have hitchhiked in the fur or feces of animals. Plants have thrown into the ocean seeds that would wash up on far away shores and become the latest new plant. Where these plants have been successful, they have been instructive to humans who would find uses for them. We can look at the wide range of plants such as red maple (Acer rubrum) that survives Canadian winters and Florida summers and find it has many uses. Spruces and firs native to the mountains and the arboreal north do less well in climates with night time temperatures in the 70s. Many plants that we name “herbs” do well in the poor rocky soils of their native Mediterranean climate. Some may be more difficult to grow in warm, poorly aerated soils of the southeast; others seem not to mind. What does that mean? Bald cypress (Taxodium distichum) thrives in southeastern swamps. It also thrives in heavy, dry soils of Fort Worth Texas. What does that mean? Apparently the native soil furnishes the needs of these plants; it may be that human interpretation of those needs has been faulty. While there are good reasons to use native plants, there is nothing automatic or easy about using them well. We must take responsibility for being good gardeners, and use of native plants does not excuse irresponsible landscape management. To be grown successfully in the landscape, native plants may need all the care and attention of their exotic, non-native relations. It begins with matching the plant to the site. Native plants survive in regions that provide the minimum for those plants to merely survive. For those plants to thrive may require more. Plants survive and thrive in response to the things provided by soil, rainfall in the right amount at the right times, hot or cold temperatures, duration and quantity of sunlight, and interactions with other organisms that make up their ecological address. Being native to a narrow geographic region does not mean that a plant will thrive anywhere within that region. The careful observer will notice significant changes in the natural flora in a short walk from the north-facing side of a slope to the south-facing side. There will typically be differences in not only sunlight, but also temperatures, perhaps moisture, or even the animals that browse through. The eastern white pine (Pinus strobus) has a niche in southern Chatham County between the Deep and Rocky Rivers where it grows to a mature size that is not found anywhere else in the county. For using natives in landscape plantings, one must carefully consider the planting site, which in many cases is not native itself. By the time a building is finished on a site, bulldozers, front-end loaders, backhoes, ditch witches, dump trucks, forklifts, and more may have visited the location, damaging the soil in the process. Vegetation is stripped off; soil is moved, piled, moved again, compacted. Even if the original vegetation were saved and replanted, extensive remediation would be necessary to predict success. Success with landscape plants demands that we know a number of things about the plant: size, growth rate, growth habit, maintenance needs. We must ask about the plant's tolerances and sensitivities to sun/shade, drought, cold, urban pollution, diseases, insects, wet soil, low fertility, and heat. Which portions of the plant provide color (flowers, fruits, leaves, stems), when, and how long does it persist? Is the plant adaptable to changing conditions as the landscape grows? Does it provide fragrance, and is the fragrance good or bad? Is the plant toxic to animals or humans? How do all of these conditions fit the site and the intended use for the plant in the landscape? We need to ask these questions whether the plant is native or not. There are good reasons to use native plants. They may fit the character of the site or contribute to local or national pride. They provide habitat and food sources for wildlife. They offer a broad gene pool of useful characteristics and adaptations. In short there are a lot of good plants out there. Let's not abuse them by putting them in some category that absolves the gardener of any responsibility. There are also good reasons not to use native plants exclusively. As already suggested, the planting site may not be native due to alterations. New streets, parking lots, and rooftops create excess water runoff; whether the site is at the top or bottom of a small hill may make a big difference. There are a wide range of other plants available; why impose broad limitations? Non-native plants may be pre-adapted to our sites by having developed in similar geographic areas. (A brief look a the globe will suggest reasons why so many east Asian plants are used in eastern North America.) Finally we should avoid use of rare, endangered, or wild collected plants. Collecting plants from the wild is no less than stealing from the public trust. Wild plants are seldom transplanted successfully. Deep taproots or wide-ranging surface roots may not lend themselves to digging. Rather than an addition to the garden, the trespasser often has only a dead plant. Gardeners should deal with nurseries that grow nursery propagated native plants (not the same as "nursery grown" which may have been collected from the wild and "grown" in the nursery a few weeks). And we need to be responsible. If we introduce plants that are aggressive spreaders, we need to be sensitive to neighbors who may not want those plants on their property. If the plant is a precocious seed producer, we need to be aware that birds, wind, or rushing water runoff may readily spread the seeds. Such seeds may have the potential to displace native plants on which wildlife may depend for food or cover. Who will be responsible for those seeds? Can you remove the seed heads prior to dispersal? And will you always be there? Regardless of the plant, landscape success depends on understanding the benefits of the site and the needs of the plant and matching the two. The linked list is a selected listing of a very few of the much longer list of plants that are native to or naturalized in Chatham County. That doesn't mean they could be predicted to do well in just any part of Chatham County. The county is quite diverse reaching from loamy creek bottoms to rocky ridges. We are not relieved from the obligation to be good gardeners and good citizens.