Weed or flower? Who decides?
Vinca minor's lovely violet flowers can cause gardeners to overlook the fact that they have invasive qualities in our area. (Robin Carlson/Chicago Botanic Garden photo)
— Dale Henriksen, Mt. Prospect
A: I define a weed as a plant that is growing where it is not wanted in the garden. Different gardeners will have different ideas as to what constitutes a "weed" in the garden. For example, are violets in the lawn weeds or interesting spring color accents?
There is a biological difference between a weedy plant and an invasive plant. Weedy plants readily spread, especially in disturbed areas, but generally do not pose a threat to the integrity of native plant communities. Invasive plants are usually non-native and are able to establish themselves within existing native plant communities and pose a threat to the integrity of the plant community.
When plants are introduced to a new location, either intentionally or accidentally, they can spread prolifically, out-compete native species for resources, and eventually even dominate the landscape. Buckthorn is an example of an invasive plant in the Chicago area.
Some factors common to many invasive plants include: rapid growth and early maturity, production of many seeds, wide dispersal of seeds by birds and wind, seeds that germinate quickly, few natural enemies, and an ability to reproduce vegetatively.
Use regional resources for guidance regarding invasive plants. The Chicago Botanic Garden has an invasive plant policy and a list of invasive plants in our area on the Garden's Web site at chicagobotanic.org/research/conservation/invasive/chicago/.
Tim Johnson is director of horticulture for the Chicago Botanic Garden in Glencoe. Send questions to: Gardening Q&A, Sunday, Chicago Tribune, 435 N. Michigan Ave., Chicago, IL 60611-4041; e-mail to firstname.lastname@example.org.