From the starlings that nest in the eaves of our rooftops to the geranium that sits potted on our front porch, our environment is filled with exotic plants and animals. Plants, in particular, represent a large portion of the exotics that we encounter. The apple and pear trees in our orchards, the lavender, sage, tomatoes, and eggplant in our herb and vegetable beds, and the coneflowers and coreopsis in our flower gardens were either altered from their native ancestors or have European or Eurasian origins. Exotic plants can be loosely defined as those that evolved within an area or on a continent other than the area in question. Exotic plants could also include cultivars of exotic and native species because these plants were created by human beings, not nature.
Even as a diehard native landscape designer, I occasionally incorporate exotic flowers, grasses, and sedges into my garden designs. However, plant selection from the palette of literally thousands of choices can be arduous and intimidating. If one of the tasks on your winter or spring to-do list includes the creation of a new garden or the renovation of an aged one, I have compiled a list of my favorite exotics as well as some exotics to avoid because of their aggressive tendencies. I have also included general guidelines for the soil preparation, design, installation, and maintenance of a garden bed.

To keep garden maintenance to a minimum, I use perennials that thrive in hot, humid summers and tolerate bitter cold winters characteristic of plant hardiness zones three, four, and five. I also use plants that produce hearty crops of seed and nectar to entice a diversity of avian and insect visitors. My first choices are cultivars or hybrids with roots close to their native ancestors, but I also use hardy cultivars with European and Eurasian origins.

After a long winter spent curled up on our couches in the Midwest, a great way to break the ice to our reintroduction outdoors is to think of spring flowers. Good choices for spring color in full sun to partial shade are any of the columbine or geranium cultivars. Columbine in particular is available in an assortment of colors from the gentle rose, blue, yellow, whites, and pinks of the 'Dragonfly' hybrids to the striking red and white 'Crimson Star.' Hardy geraniums range from the pink-tinged white petal variety 'Cantabrigiense Biokovo' to the magenta 'Patricia' and vivid 'Johnson's Blue.' The relatively short geranium variety 'Philippe Vapelle' produces purplish blue flowers and creates an excellent ground cover when mass planted. Jacob's ladder, equipped with low fernlike foliage and light blue bell-shaped flowers, is also a good choice for spring in a sunny or shady garden. If shades of gold and yellow are your preference, try planting one of the many varieties of Coreopsis. C.'Moonbeam' produces creamy yellow flowers and will add unique structure to any sunny garden with its soft needlelike foliage. To brighten a shade garden in spring, I recommend the dwarf goatsbeard with its delicate white flowers clustered on spikes and encircled by deep green foliage.

The hot and humid summer presents ideal growing conditions for an extensive variety of plants. If you're working with a slightly moist garden soil, the addition of Siberian iris 'Caesar's Brother,' butterfly weed 'Ice Ballet,' and Japanese iris 'Henry's White' will carry you through June and July with neat blooms of rich blues and icy whites. Add some meadowsweet 'Flore Pleno' with its cotton-candy white plumes to diversify the structure of the planting. On any rich garden soil, a combination of purple coneflower 'Magnus' and the mildew-resistant bee balm 'Raspberry Wine' provides stunning midsummer color. Adding Rudbeckia fulgida var. sullivantii 'Goldsturm' will create a sunny yellow drift for the purple and wine-colored base. For mid to late summer color on dry to moist soils you can't go wrong with the majestic lavender and rose flower spikes of the blazingstars 'Kobold' and 'Floristan Violet.' The blazingstar flower clusters arranged on tall spires are also fantastic butterfly magnets and prolific seed producers, and help sustain many a goldfinch, nuthatch, or chickadee through the winter.

It seems that many gardens are lacking sufficient numbers of fall bloomers to keep the garden vibrant from September through late October. I think when people are planning their gardens during the cold winter months, fall-blooming plants are last on the list. Aster cultivars, given their hardy nature and nutritious seed production, are great choices for a variety of soil types. New York aster will definitely stand out with its deep crimson flowers. Offset the red with the violet-blues and bright pinks of New England asters 'Hella Lacy' and 'Alma Potschke.' Boltonia cultivars, which resemble asters, are also a good hardy choice for fall from the soft pink flowers of var. latisquama 'Pink Beauty' to the bright white flowers of Boltonia 'Snowbank.' For a splash of yellow in your fall bouquet, add the goldenrod 'Sphacelata Golden Fleece.' Don't worry about your hay fever, however, as goldenrods are the unfortunate scapegoat for the allergenic annual ragweed, which blooms at the same time as most goldenrods.

Grasses have been definitely underutilized in the garden. Today there are many perennial exotics to try, but you must be careful that they are hardy enough to survive the severe winters characteristic of the Midwest and Great Plains. A hardy choice with close ties to its native origins is Panicum 'Prairie Sky.' The blue-green, almost metallic leaves and buff-pink spreading flower clusters are an attractive addition to any garden. After the first hard frost, the leaves turn bright yellow; a lively contrast to the soft winter snow. If you're looking for a shorter grass, try little bluestem 'The Blues.' Selected for its blue-green summer foliage, this plant also offers burgundy and bronze foliage after the first hard frost. In addition, its sturdy, bunchgrass growth structure keeps it upright, even under heavy snow cover. For a moist site, try the vigorous, creamy yellow variegated manna grass or the blue-gray black flowering sedge.

Many of the exotic plants that have been propagated in the United States have jumped ship with regard to their defined boundaries and continue to spread across the continent. Because their introduction and propagation typically do not come complete with their own plant and animal communities to keep them in check, they compete with and even destroy plant communities native to the United States. 'Dame's Rocket,' a showy, short-lived perennial, spreads easily by seed and competes with native flowers and grasses in moist woodlands. Reedgrass, reed canary grass, and purple loosestrife are incredibly invasive and are gaining ground in our wetlands and sedge meadows. In many cases, birds will assist with the spread of invasive exotics by gobbling up the palatable fruit. The once diverse understory of many Southern mesic forests has been primarily outshaded and ultimately outcompeted by buckthorn, Japanese honeysuckle, and Japanese barberry. Many of my clients with high hopes of creating a prairie on fallow farmland are continually plagued by perennial pea, sweet clover, and Queen Anne's lace. Crown vetch and double bird's foot trefoil, planted as a quick fix for erosion-prone hillsides, are also extremely tenacious and have set back many of my clients' best efforts at adding diversity to their landscape.

Once you have selected a site for a garden and you have eliminated any existing perennial weeds, conduct a general soil test for pH, micronutrients, and organic matter. If you have extremely poor sand or heavy clay soils with low organic levels, you will benefit by adding large quantities of well-composted material such as manure, leaves, or organic refuse to the top one to two feet of soil. Organic matter increases the water-holding capacity of sandy soils and improves the water and air circulation of heavy clays. This increased porosity enhances root development, plant growth, and ultimately plant survival. If your soil is acidic, add garden lime to correct the pH to within one to two points of the neutral level of 7 pH.

To generate a plant inventory, plan on one plant per one to two square feet and choose flowers with a variety of blooming times so you will have bird cover and food sources and landscape interest throughout the growing season. In addition, budget for an even mix of grasses and flowers to keep your maintenance to a minimum. In addition to their beautiful colors and nutritious seed production, grasses will provide structural support for the flowers and prevent them from falling over. They also help keep out invading weeds by filling in between the flowers with their fibrous root systems.

To install your garden plants, till the planting area down approximately one foot to create an easy-to-work planting bed, which will accommodate the root length of each plant. Plant the transplants approximately one to two feet on center and according to your plan. Dig a hole large enough to spread out the root structure of each plant, and firm the soil around the roots to prevent air pockets. Mulch around each transplant (not over it) with three to four inches of weed-free straw. Mulch will help retain moisture in the soil and reduce the weed invasion between the young plants. Place a marker, such as a popsicle stick, with the name of the transplant next to the plant to avoid accidentally pulling it out during weeding and to help you identify it later.

During the first four to six weeks after planting, water every other morning for 15 to 30 minutes, especially if planted in late spring or in sand or clay soils. Watering should be continued after six weeks only during prolonged dry periods. Be careful not to overwater or water at night because fungus could attack transplants under cool, damp conditions. Watering is not recommended after the first growing season; it will encourage the roots to develop near the surface. Deep root development is necessary to keep the plant alive during periods of drought.

First-year weed control is required to reduce the competition between weeds and transplants for water, light, and space. Pull out any perennial weeds and pull out or cut back annual and biennial weeds before they go to seed. Make sure to remove the entire root of perennial weeds or they will return from the root that remains in the soil.

Weeding and watering during the first year will create a solid foundation for strong, healthy plant growth. Using a diverse combination of hardy perennials as building blocks will minimize your garden maintenance through the years. Avoiding the aggressive exotics will maintain the diversity of your personal garden and help to reduce the spread of these unruly invaders into our surrounding native plant communities.
Jennifer Baker is a consulting ecologist and land planner/landscape designer in Wisconsin.


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