Invasive plants aren’t just for teaching science


boys on invasive pull

Fifth-graders removing aggressive alien vines as part of an invasive plant pull in the park that Belvedere Elementary (Falls Church, Va.) has adopted as an outdoor classroom.

So near the 271st anniversary of Thomas Jefferson’s April 13 birthday, I wanted to take a few moments to thank him for exhorting his countrymen to deluge the new nation with new types of vegetation and for providing me, centuries later, with so many rich, hands-on opportunities to teach students not just about the environment, but about history, too. By which I mean, thankyousomuch for the invasives.

Thomas Jefferson by Rembrandt Peale, circa 1800. ©Public Domain.

Thomas Jefferson by Rembrandt Peale, circa 1800. ©Public Domain.

Mr. Jefferson’s exact words were, “The greatest service which can be rendered to any country is to add a useful plant to its culture.”

He took his own call to action seriously, introducing (as did Benjamin Franklin and George Washington) more than his fair share of plants to the East Coast. He cultivated 330 varieties of 89 species of vegetables and herbs; he also grew 170 varieties of fruit. He’s often credited with bringing in Scotch broom, which he used in the creation of a gigantic labyrinth at Monticello.

But the operative word in his pronouncement is “useful” — and by this he meant economically useful. He was thinking along the lines of rice and bread grains.  Jefferson “lacked 200 years of hindsight to be able to judge whether certain introduced species might become the pests, the bullies, the weeds of the garden world,” Monticello Gardens and Grounds Director Peter Hatch  wrote in “Garden Weeds in the Age of Jefferson.”

Mr. Jefferson also was just saying in a statesmanlike way what so many others had been doing for 300 years. In the 16th century, the Spanish brought Central America’s sapodilla tree to Florida, where today its stands grow so thick that natives can’t survive the shade. The English government encouraged colonial farmers to grow non-native crops like sugar cane so it could wean itself off foreign sources. By the early 1600s, John Smith noted that the “herbs and roots” in the fields around Jamestown appeared to be the same as those in England.

By 1759, though, America’s first homegrown botanist, John Bartram, complained in a letter about St. John’s wort, which he declared “pernicious.” A few decades later, Mr. Jefferson faced his own troubles with invasive plants. Of the worst offenders at Monticello today, at least five were already posing problems prior to 1832: Bermuda grass, chickweed, crabgrass, wild onion, and a variety of briars.

So why were they brought to the United States in the first place? Here’s the backstory of a few:

  • Crabgrass (Digitaria sp.) was planted on purpose because livestock ate it, and it grew in the late summer heat when everything else was dead or dormant.
  • Purple loosestrife (Lythrum salicaria), present since colonial days, most likely arrived in ship ballast or livestock feed or bedding, although it was also imported as a garden ornamental. A single plant can produce well over 1 million seeds a season. Oops.
  • We can thank German immigrants for Common St. John’s wor(Hypericum perforatum), which they believed would exorcise the devil. Instead, it plays the devil, beating out the natives for resources and producing more than 30,000 seeds per plant. On the upside, it can be used for the mild depression you may fall into while trying to drive it out of your yard. To make matters confusing, there are native Hypericum species.
  • Porcelainberry (Ampelopsis brevipedunculata), Oriental bittersweet  (Celastrus orbiculatus) and kudzu (Pueraria montana var. lobata) came in as ornamentals from Asia.

Learning about the exuberant race to import species into the United States gives students a clear picture of what it was like in our young nation and what it was like to be a pioneer. The soil was often untillable and the plants that did exist were unfamiliar. On almost every invasive plant pull I’ve led, at least one student stops after a few minutes of pulling or digging to wipe his or her brow and pronounce, “I would hate to be a farmer. It’s hard work.”

Sure. A farmer, a house builder, a road builder, a ditch digger, and so on. Establishing the United States was hard work. Students can follow the arc of agriculture and international relations through the mid-1800s, during which the US government gave exotic seed and plants to farmers and plant trades between the US and Asia exploded. The arc begins to descend around 1912, when Congress passed the Plant Quarantine Act to calm nationwide worries about pest problems in nursery plants.

After that there was a series of regulatory programs for plant introduction, but each one was about as effective on kudzu as every other elimination method attempted. Kudzu was included in the Japanese garden of native plants at the 1876 Centennial Exposition in Philadelphia, and consumers in the South started buying it to shade their porches or give it to animals for forage. In the 1930s,  government crews planted thousands of acres of it to control erosion. A decade later, the government paid farmers $8 an acre to plant it in old fields, again to control soil runoff. The US Department of Agriculture didn’t stop approving kudzu as a cover crop until 1953.

As is often said, the past is prologue, and so teaching students about these  eagerly introduced plants can also be a way of showing them why it’s important to slow down and think long-term when making their own decisions. After all, 300 years later we’re still paying for the decision to import English ivy. Its glossy green vines graced colonial buildings, but the weed didn’t stop there. In short order, it made its way west.

English ivy

Today it’s doing just fine, still being sold in garden centers and home improvement stores, then set free to strangle trees and literally smother the competition in more than half of the United States and lower Canada — despite being declared invasive in 18 states and Washington, D.C.

For more information on using invasive plants with your students:


© 2014, Stacey Evers. All rights reserved. This article is the property of We have received many requests to reprint our work. Our policy is that you are free to use a short excerpt which must give proper credit to the author, and must include a link back to the original post on our site. Please use the contact form above if you have any questions.

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