With the most grueling days of summer behind me, I turn my attention to my neglected yard. It’s time to thin plants, remove weeds and perhaps even put in new plants. Fall is the best time of year to plant.

But one has to be careful when choosing plants. It’s easy to unknowingly introduce an invasive plant. Many times homeowners don’t even know that a plant in their yard can become a menace in the wild. Meanwhile, some common landscape plants found at most nurseries are invasive, growing out of control.

Invasive plants share a few common qualities that make them a threat to the natural areas: spreading aggressively by runners or rhizomes; producing large numbers of seed that survive to germinate; and dispersing from the parent plant through various means, including wind, water, wildlife and people.

The majority of these invasive plants are also nonnative. Plants native to North America are generally recognized as those occurring on the continent prior to European settlement.

Many nonnative plants have great economic value for agriculture, forestry, horticulture and other industries and pose little to no danger to our natural ecosystems. Others pose a serious ecological threat.

Because they have been introduced into an environment in which they did not evolve, there are no natural predators, parasites or other controls to keep these nonnative, invasive plants in check. Invasive species grow fast and mature early in the season and reproduce profusely. Some invasive vines can actually bring down trees by their sheer weight.

These aggressive plants outcompete and eliminate entire native plant communities. They change the composition of the landscape. The ecological balance of plants, animals, soil, and water achieved over many thousands of years is destroyed.

As native plants are displaced, animal populations that rely on the plants for food and shelter also decline. When invasive plants take over wetlands, forests or meadows, we lose the native plants and the habitats that local wildlife need.

In the United States, invasive plants already infest more than 100 million acres and continue to increase by 8-20 percent annually.

Once established, invasive plants require enormous amounts of time, labor and money to control or eliminate. Invasive species cost the United States an estimated $34.7 billion each year in control efforts and agricultural losses.

Invasive plants also affect recreational activities in natural areas such as boating, bird watching, fishing and exploring. Some invasive species become so thick that it is impossible to access waterways, forests and other areas.

Homeowners, can help, however. Be careful when choosing plants. Some common landscape plants do not abide by boundaries, and it is not difficult to unwittingly plant a species that is very prolific, spreading beyond the original plant site to overtake hundreds of acres of land.

Become familiar with invasive plant species in your area and avoid planting them. Ask for native plant alternatives at your nursery. If you already have invasive plants on your property, consider removing them and replacing them with native species. Here are few troublesome plants to avoid.

Nonnative invasive: purple loosestrife (Lythrum salicaria)

Native alternatives: blazing star (Liatris spicata), New York ironweed (Vernonia noveboracensis), obedient plant (Physostegia virginiana), Joe-Pye weed (Eupatorium dubium)

Nonnative invasive: common daylily (Hemerocallis fulva)

Native alternatives: wood lily (Lilium philadelphicum), Canada lily (Lilium canadense), ox-eye sunflower (Heliopsis helianthoides)

Nonnative invasive: Chinese wisteria (Wisteria sinensis) or Japanese wisteria (Wisteria floribunda)

Native alternatives: American wisteria (Wisteria fructescens), trumpet creeper (Campsis radicans), trumpet honeysuckle (Lonicera sempervirens)

Nonnative invasive: English ivy (Hedera helix) or Japanese Pachysandra (Pachysandra terminalis)

Native alternatives: alum root (Heuchera americana), white wood aster (Eurybia divaricata), foam flower (Tiarella cordifolia), partridgeberry (Mitchella repens)

Nonnative invasive: Winged burning bush (Euonymous alata) or Japanese barberry (Berberia thunbergii)

Native alternatives: red chokeberry (Photinia pyrifolia [formerly Aronia arbutifolia]), Virginia sweetspire (Itea virginica), highbush blueberry (Vaccinium corymbosum)

Nonnative invasive: Tree of heaven (Ailanthus altissima)

Native alternatives: staghorn sumac (Rhus typhina), ash (Fraxinus pennsylvanica or americana), black walnut (Juglans nigra)

Nonnative invasive: Bradford pear (Pyrus calleryana ‘Bradford’)

Native alternatives: redbud (Cercis canadensis), serviceberry (Amelanchier canadensis), southern arrowwood (Viburnum dentatum), flowering dogwood (Cornus florida)

Contact your local native plant society for more information about invasive plants and native plant alternatives. For control of exotic species, contact your state university Cooperative Extension Service.

Internet Joins Forces Against Invaders

The National Park Service and U.S. Fish and Wildlife Service have created a guide, “Plant Invaders of Mid-Atlantic Natural Areas.” The color guide describes common invasive species and native plants to use in their place. To download a copy, go to http://www.nps.gov/plants/alien/pubs/midatlantic

For information, one can also visit the Plant Conservation Alliance’s Alien Plant Working Group’s website at www.nps.gov/plants/alien/ or the USF&WS Chesapeake Bay Field Office’s website at http://www.fws.govchesapeakebay and click on BayScapes.