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World Roots of Southern Gardens and Non-Native Plant Invasions [Image: Flowering azalea] [Image: Water hyacinth on a Louisiana bayou] [Image: cat’s claw vine] The United States is a nation of avid gardeners. We garden for food and for pleasure, and since the earliest European colonists arrived here almost 600 years ago, we have relied on an enormous number of plants from all parts of the world to populate our gardens. Pleasure hasn’t always been the main goal of gardening, as it is for many people today. For the earliest settlers, gardening was a necessity, and colonists needed the security of having familiar plants they could rely upon for food, drink, medicine and fiber. Without these plants, survival was difficult. But, as new technologies developed, meeting the needs of everyday living became easier, and many Americans expanded their gardening activities to include the pleasure of growing ornamental plants. The transformation from a nation of practical gardeners to ornamental gardening enthusiasts has relied heavily on the continued efforts of botanists, plant explorers and horticulture enthusiasts to introduce new species and varieties, to produce them in quantities large enough for retail and to promote gardening to the public. One result of the move to pleasure gardening is that there is always a demand for new species and varieties of plants. Today, many of our favorite garden plants come from other parts of the world. Here in the South, our dependence on introduced plants in ornamental gardening is especially noteworthy. Look in your yard and you will find several of the Southern Favorites listed in Table 1. The surprise is that, in fact, many of our so-called Southern heritage plants originate in other parts of the world! Table 1. Many garden and landscape favorites in the South originate in other parts of the world. Southern Favorite Scientific name Common name Place of origin Agapanthus africanus Lily of the Nile Africa Albizzia julibrissin Mimosa tree Asia Aspidistra eliator Cast iron plant Asia Camellia japonica Camellia Asia Camellia sasanqua Sasanqua Asia Cleome hasslerana Cleome Cen./South America Colocasia esculenta Elephant ear Asia Digitalis purpurea Foxglove Europe Gardenia jasminoides Gardenia Asia Gladiolus byzantinum Gladiolus Africa Hemerocallis fulva Daylily Europe/Asia Hibiscus syriacus Althaea Asia Hippeastrum spp. Amaryllis South America Hosta albomarginata Hosta Asia Hydrangea miacrophylla Hydrangea Asia Ilex cornuta Chinese holly Asia Lagertsroemia indica Crape myrtle Asia Ligustrum sinense Chinese privet  Asia Ligustrum japonicum Wax leaf ligustrum Asia Lonicera japonica Japanese honeysuckle Asia Magnolia soulangiana Japanese magnolia Asia Magnolia stellata Star magnolia Asia Nandina domestica Nandina Asia Narcissus jonquilla Jonquil Asia Narcissus pseudonarcissus Daffodil Europe Narcissus tazeta Narcissus Europe Nerium oleander Oleander Europe/Africa Ophiopogon japonicus Monkey grass Asia Osmanthus fragrans Sweet olive Asia Plumbago auriculata Cape plumbago Africa Rhododendron indica Azalea Asia Spiraea prunifolia Bridal wreath spirea Asia Trachelospermum jasminoides Confederate jasmine Asia Wisteria sinensis Wisteria Asia  Zinnia elegans  Zinnia Cen./South America Growing plants that are native to other regions of the world can be fun and interesting, but with the introduction of so many different species over the years, a small number of ornamental plants have become naturalized in the environment. Being naturalized means that the plant can survive and reproduce outside of the confines of the garden and the yard. Most naturalized species are not thought to harm or disrupt the ecosystems where they naturalize, but in a few cases, naturalized plants have a negative effect on other organisms. At that point, the naturalized species is considered invasive. Invasive plant species can have direct impacts on the systems they invade – for example they can form monocultures that exclude native plants (example: kudzu overgrowing and choking out forest trees). They can also have indirect impacts on systems, changing the way forest fires burn, altering water temperatures (example: water hyacinth forming dense mats that shade the water) or changing food and shelter availability for wildlife. In situations where invasive plants cause ecological harm, it is highly desirable to manage them to reduce the impact on the system. It is also desirable to prevent further introductions of these species.  In truth, not all invasive plants were introduced deliberately, and only about half of the invasive plant species here are sold or traded for ornamental gardening. But when you shop for plants for your landscape or garden, you may wish to take the potential for being invasive into consideration when making your selection. In the nursery, about three out of every four species are non-native, and of the non-native species for sale, about one in ten has been reported as invasive somewhere in the Southeast. So take care with plant selection. Talk to your nursery owner or a horticulturalist about the plants you are considering. Ask the following questions: Is this plant aggressive (fast growth, heavy seed production)? Does it produce a lot of volunteers or is it known to be weedy? Does it take a lot of care to “keep in check"? Were does the plant come from originally? If it gets out of hand, is it hard to kill? Is it one of those plants anyone can grow and most cannot kill? If a plant sounds very, very easy to grow and it comes from another part of the world, it just might be too good to be true. Remember that not all invasive plants were created equal. Some will be more or less aggressive, depending on the species and the growing conditions. For example, English ivy is very aggressive in the Pacific Northwest, but behaves itself pretty well in the Southeast. Coral ardisia forms large monocultures in the loessal hills of the Feliciana Parishes and in the sandier wet soils of the Gulf Coast, but it seems not to expand in areas with heavy, wet, clay soils such as those in the Mississippi River floodplain and in the Houston area. Some plants that you may find for sale but that you may want to avoid are listed in Table 2. Remember that your garden and your yard are part of a larger landscape. The choices you make in your garden can have an impact elsewhere. Table 2. Many plant species that show invasiveness in Louisiana and elsewhere are sold commercially in nurseries. Leaving these plants at the nursery can help keep Louisiana’s natural places native. Scientific name Common name Place of origin Ailanthus altissima Tree of Heaven Asia Albizzia julibrissin Mimosa, silk tree Asia Ardisia crenata Coral ardisia Asia Broussonetia papyrifera Paper mulberry Asia Cinnamomum camphora Camphor tree Asia Colocasia esculenta Elephant ear Asia Dioscorea bulbifera Air potato Africa/Polynesia Eichhornia crassipes Water hyacinth Asia Firmiana simplex Chinese parasol Asia Hedera helix English ivy Europe Hydrilla verticilatta* Hydrilla Asia Ilex cornuta Chinese holly Asia Imperata cylindrica ‘Red Baron’** Red Baron grass Pacific Ligustrum japonicum Wax leaf ligustrum Asia Ligustrum sinense Chinese privet Europe/Asia Lonicera japonica Japanese honeysuckle Asia Lygodium japonicum Japanese climbing fern Asia Macfadyena unguis-cati Cat’s claw vine Cen./South America Melia azedarach Chinaberry Asia Nandina domestica Nandina Asia Peuraria lobata Kudzu Asia Salvinia molesta* Giant salvinia Cen./South America Salvinina minima Common salvinia Cen./South America Triadica sebefera Chinese tallow Asia Wisteria sinensis Wisteria Asia *Included on the APHIS USDA Federal Noxious Weed List (http://www.aphis.usda.gov/ppq/weeds/) **This is a dwarf, red form of Imperata cylindrica, included on the APHIS USDA Federal Noxious Weed List

Posted on: 6/18/2006 4:20:45 PM