Extension Educator, Horticulture
As we select what plants to grow this year, there are a few plants that can not 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.
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."
Japanese honeysuckle (Lonicera japonica), multiflora rose (Rosa multiflora), and purple loosestrife (Lythrum salicaria) have been legally designated as exotic weeds. There are several worthy candidates for additions to the list such as kudzu and garlic mustard. I just spent time at my favorite woodland viewing how garlic mustard can choke out my beloved wildflowers.
As the act reads: "It shall be unlawful for any person, corporation, political subdivision, agency or Department of the State 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 Conservation (now Department of Natural Resoures)."
In other words, don't buy, sell or plant these plants and don't give them to your friends or enemies. Since the law covers just Illinois, these plants may be available for purchase in other states. You may have noticed the fine print in catalogs "not for sale to residents of Illinois" next to a plant listing.
Many of the exotic weeds started out or are used as garden plants. For instance, purple loosestrife is a very pretty plant with a spike of pink flowers all summer long. The problem is the loosestrife doesn't know when to quit or how to be a good neighbor. It proceeds to conquer the garden and the local natural areas and waterways by choking out all of the other plants including orchids and other rare plants.
The following are Purple Loosestrife cultivars (cultivated varieties) which are illegal to sell or plant: 'Happy,' 'Robert,' 'Firecandle,' 'Brightness,' 'The Beacon,' 'Lady Sackville,' 'Atropurpureum,' L. s. roseum superbum, and L. s. tomentosum.
Some cultivars are listed as legal in Illinois. However a wealth of research is showing these cultivars are not as harmless as once thought even though they are derived from a different Lythrum (Lythrum virgatum). Supposedly the seeds are sterile and will not reseed. Research has shown the pollen is viable and will pollinate the weedy species.
To see what Illinois is doing to try to manage purple loosestrife, check out the Purple loosestrife biological control program at the Illinois Natural History Survey at www.inhs.uiuc.edu/cbd/loosestrife/bcpl.html.
Rather than worrying about which loosestrife is correct, why not try some beautiful alternatives such as blazing star (Liatris), dragonshead, Physostegia, Veronica 'Barcorolle,' Salvia 'Amethyst' or 'Rose Queen,' or Culver's root (Veronicastrum). They are all perennial plants with beautiful spike flowers like loosestrife minus the nasty weedy tendency.
Being a devoted plant collector, it is difficult for me to not grow something I think is beautiful such as purple loosestrife. I've tried to defend myself by saying I had the sterile cultivars and I didn't live near a wetland. However when I realize the consequences, it becomes very easy to compost my purple loosestrife plant. I believe we all must be responsible gardeners. You think you have weed problems, just try weeding a 600-acre woodland.
Don't forget the workshop at the Idea Garden on South Lincoln May 15 at 10 am on Windowbox Gardening.