Easy Gardener • Pat Howell
	Weeding in the Garden of Good and Evil

This February, Brookside Gardens held the first ever (in this area) symposium on Exotic Invasive Plants. At a cost of $70 per person, the auditorium was sold out, with 200 attendees, and another hundred turned away!

What is An Invasive Plant?

Invasive Species have been called biological pollution. They are "alien species whose introduction does or is likely to cause economic or environmental harm or harm to human health." (Presidential Executive Order 13112, 2/3/99).

Just a few years ago, the issue of invasive plants did not seem to be an issue at all, except to conservationists, horticulturists, and government agencies.

Yes, there were a few plants in our gardens that spread easily; at times we cursed them; other times we appreciated their fast-growing, tough characteristics or other features.

Examples: beautiful flowers: Japanese Wisteria; fantastic fragrance: Japanese honeysuckle; drought tolerance: English ivy; cheap: Barberry species.

Now, these biological polluters are destroying America’s natural history and therefore our national identity. It is generally agreed that invasive species are the second-greatest threat to biodiversity after outright habitat destruction. Invasives are taking over public lands at the rate of 4,300 acres a day, according to one source.

Wherever we don’t have the manpower or equipment to keep them in check, invasive species have escaped cultivation and are posing a serious threat to our natural ecosystems by invading wildlife habitats and choking out native species.

Along the Hiker-Biker Trail one can hardly miss: Japanese knotweed, multiflora rose, kudzu, and ivy climbing and killing trees.

What Makes an Invasive Plant Harmful?

An alien species, also called non-native, non-indigenous, or exotic, is one that is introduced, accidentally or purposefully, into an ecosystem in which it did not evolve. Alien or exotic species can come from other continents, other countries, and even other parts of the United States.

Invasive species often exhibit certain characteristics: they spread aggressively, reproduce quickly, have short juvenile periods, tolerate a wide range of climatic conditions and habitats, compete efficiently against other species, and thrive in disturbed areas.

Unfortunately, the pests and diseases that keep these exotic populations under control in their regions of origin are not present in Maryland. Most of Maryland’s invasive species come from somewhere else in the world.

How did Invasives Get Here?

Some invasive plants have come to the US by accident, in soil or crop seed. They can be carried in ship ballast, or hitchhike on imported goods. Most have come to this country intentionally, however. Kudzu (‘the vine that ate the South’) was planted as an erosion control in the 1930’s and 40’s. Invasives have also often been planted as windbreaks and wildlife food. More than half of North America’s invasive plants were brought into the country for use as garden ornamentals.

Some of these have escaped from arboreta, botanical gardens, and our own backyards.

Their qualities give invasive plants the ability to overwhelm and displace existing native plants by reducing the availability of light, water, nutrients, and space. The worst invasives completely displace natives, forming dense one-species stands (monoculture) and can also change soil fertility, hydrology, fire regimes, and other features of an area. Fewer native plants mean less habitat and fewer food plants for native insects and other wildlife.

What Can you Do?

Learn how to spot invasives. Scout for invasive species. Remove invasive species before they become a problem. Avoid introducing invasive species. Avoid transporting invasive species. Minimize disturbance. Spread the word.

Watch future columns for ideas for alternatives to plant in our gardens.

Some helpful websites:

www.mdinvasivesp.org

Weeds Gone Wild: Alien Plant Invaders of Natural Areas: http://www.nps.gov/plants/alien/factmain.htm.

The Nature Conservancy, Wildland Invasive Species Program: www.tncweeds.ucdavis.edu/esadocs.html.

www.invasivespecies.org/

If you would like to be informed of the next Green Matters symposium, join the Friends of Brookside Gardens, 301/962-1435.

Pat Howell is a Takoma Park gardener and landscape designer/garden-builder, and welcomes comments, advice, suggestions, complaints. She is available for hand-holding and answering questions through Deephaven Landscapers.