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Invasive
Plants and Animals Gardeners Beware! You might be surprised to learn that some plants considered to be invasive in Illinois may be sold at our local nurseries, or passed along from gardener to gardener. We commonly plant the offenders in our gardens, particularly because they are so easy to grow. Unfortunately, if they "escape" to the woodlands or prairies, they can become difficult to remove. It's best not to plant them in your garden at all, but if you do, watch that they don't spread into native areas. Here is a list of some plants to avoid, or carefully control:
Visit the Chicago Botanic Garden website for a list of invasive plants and alternatives that you can choose in their place.  Buckthorn
(Rhamnus spp.)There are two species of buckthorn found in Riverwoods. Rhamnus cathartica, the Common Buckthorn pictured here, is in fact, the most common. This small tree or shrub leafs out early in the spring and doesn't drop all of its leaves until very late in the fall. Their dense shade throughout the growing season will not allow native plants to survive. Mature buckthorn will produce branches filled with seeds that fall to the ground or are spread by birds, planting new buckthorn everywhere. The other species, Rhamnus frangula, is more often found in wetlands or open moist areas. Either species can be controlled by cutting and painting the stump with herbicide. Additional spraying may be necessary in the spring. This is a good fall activity because it is easy to identify the buckthorn when it is the only shrub or tree left with leaves. It's a good winter activity too -- no bugs, no rain and a good time to burn. Learn more about buckthorn at The Minnesota Department of Natural Resources or The University of Minnesota Extension Service.  Bush
Honeysuckles
(various species)The pretty pink or white flowers of the honeysuckle bushes produce berries eaten by birds and then spread throughout our forests. Walking through Riverwoods, you will see them blooming along the roadside and driveways in the spring. They can even be found deeper in the woods, though they rarely flower there. Like the buckthorn and multi-flora rose, the Bush Honeysuckles compete with native shrubs and shade out the native ground plants. For more information, see the descriptions at the the Illinois Natural History Survey.  Canada
Thistle (Cirsium
arvense)New to Riverwoods, the Canada Thistle can be seen along the roadsides and in open areas, even in the woods. This plant needs sun to thrive, but our thinning woodlands and the non-wooded areas of Riverwoods offer places for it to become established. It is taking advantage of every site where it is left to spread. As well as spreading by seed, Canada Thistle has deep roots that spread underground, quickly creating thick stands that are difficult to remove. If you have Canada Thistle on your property, remove it before it gets out of hand. For more information, see the Plant Conservation Alliance's Alien Plant Working Group or the Colorado State University Cooperative Extension website.  Common
Reed (Phragmites
australis) Common Reed is not a reed, but a grass. This tall, stately plant can easily grow well over 12 feet! There is a native variety of Phargmites australis, as well as subspecies that were probably accidentally introduced from Europe in the late 18th or early 19th century in shipping ballast -- and aggressive hybrids that have developed over the years. Whether native or not, this plant can quickly take over large wetland habitats, choking out other plant species. The grass produces large seed heads, but the seeds are not too viable. Mainly, the plant spreads by rhizomes which can grow outward to 10 feet and several feet deep, in one season, if conditions are good. Dense stands are difficult to remove and once established, make wetland restoration very difficult.In some parts of Europe, Phragmites australis populations are declining, raising a concern opposite from ours in the U.S. Learn more about Phragmites at the Wisconsin Wetlands Assn., or the NYC Department of Parks and Resoration websites.  Common
Teasel (Dipsacus
fullonum)Common Teasel
is found in sunny areas and is marching across America along the highways
and byways of the country. This prickly plant establishes thick stands
along roads, in pastures and in the open meadows of our forest preserves.
Creeping
Charlie - Ground Ivy (Glechoma
hederacea)Creeping Charlie, sometimes called Ground Ivy, is usually thought of as a common nuisance lawn weed that is difficult to control. Unfortunately, it has also spread to natural areas, particularly moist shady areas like those in Riverwoods. Very large colonies can be seen near the Des Plaines River. In the spring, the plant produces small purple flowers. By fall, the plant colonies grow, as stems reach out and root into the ground. Click here for a USDA document about Glechoma hederacea.  Garlic
Mustard (Alliaria
petiolata)Garlic Mustard is one of Riverwoods' most rampant invasive plant species. It can spread through the woodlands very quickly, soon covering the forest floor and outcompeting all native non-woody plants. In just a few years, acreage can become a monoculture of garlic mustard. Each plant can produce thousands of seeds. They fall to the ground or are carried to new locations by people and wildlife. The seeds can remain viable for in the soil for five years and even longer. Garlic Mustard is a biennial, a plant with a two-year life cycle. The first year seedlings are small rosettes, close to the ground. The second year, plants grow up to 3 feet tall, producing many small flowers and long thin seed pods. Removing stands of garlic mustard is a challenge. To bring it under control, several years of patient eradiction is needed. But the results will be worth the efforts required. Learn more about Garlic Mustard and options for control at the Plant Conservation Alliance website. Gypsy Moth (Lymantria dispar) Gypsy Moths have been found in several areas of Riverwoods. Please check your property. Click here to see the life cycle by month. If you see any, call Nancy at the Village Hall (847-945-3990). Click here to visit the USDA Forest Service Site for information. Click here for a list of Gypsy Moth tree preferences.
 Indian
Strawberry (Duchesnea
Indica)You may notice new strawberry plants spreading through your property. Check them carefully -- if they have yellow flowers and hollow, tasteless berries, they are Indian Strawberry. Our native strawberries have white flowers and if the birds don't eat them first, and there are any left for you to try, they are tiny and sweet. Indian Strawberry is beginnng to spread in Riverwoods. Once it takse hold, it becomes difficult to remove, so pull them or treat them with RoundUp® as soon as you find them. This is not a good groundcover! Indian Strawberry is on the Chicago Botanic Garden list of invasive plants in the midwest. Check out their site to see the other plants listed. Photo: Bodner, Ted. Southern Weed Science Society. www.invasive.org
A gold variety is sold for gardens. It's best not to plant Creeping Jenny in Riverwoods, but if you do, be careful to watch that it doesn't spread into the woods. With its small breakable roots, it is very difficult to eliminate. Learn more about moneywort at the Illinois Wildflowers site or from the USDA Forest Service.  Multiflora
Rose (Rosa
multiflora) Following buckthorn, Multiflora Rose is one of the most invasive woody plants in Riverwoods. It is beautiful in the spring, covered with clusters of white flowers, but its thorns make it very nasty to remove and it spreads easily. Multiflora Rose is common along the edge of the woods and in sunny areas. It grows into a dense, high, spreading thicket of plants. For more information, see the descriptions at the Wisconsin DNR or the Illinois Natural History Survey.  Norway
Maple (Acer platanoiodes)The Norway Maple is a large, fast growing ornamental shade tree that was planted in the boulevards and parkways of many cities. Native to Europe, it has spread to the woodlands, easily becoming established in disturbed forest habitats. It even outcompletes the Sugar Maple (Acer saccharum), a very shade tolerant native species. How can you tell if it's a Norway Maple? - In the spring or summer, break off a leaf -- a milky white sap is in the stem. - The wings of Norway Maple seeds are very widely spread, not V-shaped. - In autumn, Norway Maples don't turn the bright red-orange colors of the Sugar Maples and they change color very late in the season. - In the winter, look for a distinctive greenish, red bud. It has a large center bud flanked on each side by smaller ones. Maples have opposite branching, so farther down the twig, you'll see side buds, one on each side of the twig. Native maples have very small, tight, brown buds. Learn more about Norway Maples at: Plant Invaders of Mid-Atlantic Natural Areas. See a map of the states where the Norway Maple is considered invasive. 
Purple
Loosestrife (Lythrum salicaria)Purple Loosestrife is a beautiful perennial that forms dense stands in moist open areas. From June through August, you can see its magenta flowers blooming along many of our highways and filling fields with brilliant color. Not surprisingly, it was introduced in the 1800's as a garden plant and herb and also arrived as seeds in the ballast of ships and the wool coats of sheep. Unfortunately, purple loosestrife has made itself at home here, taking over areas to the exclusion of other plants and reducing habitat for wetland animals and birds. Illinois has had some success in experimental areas controlling the plant using species-specific beetles. If you have purple loosestrife on your property or in your garden, remove it. The State of Illinois outlaws the sale of purple loosestrife and it is even on the list of plants eBay will not allow to be sold on its site. Learn more about purple loosestrife at the Plant Conservation Alliance website. Websites with information about invasive species Chicago Wilderness - lots of info from the largest alliance of natural areas in the Chicago region Wisconsin Department of Natural Resources The United States National Arboretum |
Watch
for the following invasive species and whenever possible, remove
them from our woodland environment.
Japanese
Barberry (Berberis
thunbergii)
Moneywort
/ Creeping Jenny (Lysimachia
nummularia)