The Homeowners Column

The Homeowners Column

Insidious Invasive Plants

Photo of Sandra Mason

Sandra Mason
Extension Educator, Horticulture
slmason@illinois.edu

A gardener's goal is to help plants thrive. But some plants thrive a bit too much and quickly move from treasured acquisition to scorned trespasser. Weeds are plants out of place whether they came with a price tag or not.

As we select what plants to grow this year, a few plants cannot be legally grown in Illinois. It's not just ragweed, Canadian thistle or marijuana. There are other illegal plants perhaps not as well known that are listed in the Illinois Exotic Weed Act.

Within the Act the definition of exotic weeds are: "…plants not native to North America which when planted either spread vegetatively or naturalize and degrade natural communities, reduce the value of fish and wildlife habitat or threaten an Illinois endangered or threatened species."

Legally designated exotic weeds are: Japanese honeysuckle including the cultivar 'Hall's' (Lonicera japonica), multiflora rose (Rosa multiflora), purple loosestrife (Lythrum salicaria), kudzu (Pueraria lobata) and six species of buckthorn (Rhamnus spp. including glossy buckthorn R. frangula, common buckthorn R. cathartica and their cultivars).

As the act reads: "It shall be unlawful for any person, corporation ... to buy, sell, offer for sale, distribute or plant seeds, plants or plant parts of exotic weeds without a permit issued by the Department of Natural Resources."

In other words, don't buy, sell or plant these plants and don't give them to your friends or enemies. Since this Act is limited to Illinois, these plants may be available for purchase in other states. The fine print in catalogs will state "not for sale to residents of Illinois".

Unfortunately numerous worthy candidates exist as additions to the exotic weed act, but plants move faster than politics. A great deal of time and resources are spent trying to eradicate exotic weeds including ones that are not legally designated. Master Naturalists and other volunteers recently removed over 1200 pounds of garlic mustard during the Great Garlic Mustard Hunt. You think you have weed problems, just try weeding hundreds of acres of woodland.

The severity of a plant's invasiveness depends on an area's soil and environmental conditions. Some plants are invasive in other parts of the country, but are not commonly invasive here. However we must remain observant. If a garden plant is popping up all over your garden and yard, a red flag should unfurl and smack you in the face declaring this plant has no boundaries and has the way and the will to go beyond your garden into natural areas.

Invasive plants often have one or more of these characteristics that make them over-achievers.

  • Rapid growth and early maturity. Plants go from seed to producing more seed very rapidly.
  • Prolific flowers and therefore prolific quantities of fruit are produced.
  • Birds love to eat the fruit; a particular problem with invasive trees and shrubs.
  • Birds also love to fly to other areas and deposit their newly ingested seeds.
  • Lack of natural enemies and pests. Native plants can be weeds; however, exotic plants lack the natural pests which keep their numbers under control in their home country.

Bush honeysuckles (including Tatarian honeysuckle, Lonicera maackii; Morrow's honeysuckle, L. morrowii; and Amur honeysuckle L. tartarica) are the poster children for exotic invasive shrubs. They produce abundant fruit which birds love to eat. Bird food, that should be a good thing, right? Unfortunately the fruit is about as nutritious as a bag of potato chips.

May is invasive species awareness month. Do your part to protect our natural areas from space invaders. Check out the list of Invasive Plants of East Central Illinois and their alternatives.

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