ONE OF THE EASIEST WAYS TO CONTROL WEEDS is by taking advantage of carefully chosen aggressive plants in order to prevent unwanted plants from gaining a foothold. I've been trying to apply this principle in landscaping my front yard, as documented in the "My Forlorn Front Yard" series.
Today I read an interesting article on this topic posted to the Native Gardening group on Yahoo! Groups. In this Oct. 1, 2007, which was carried by the Associated Press, author Dean Fosdick interviewed Leslie Weston, until recently an associated professor of weed management at Cornell University. According to Weston, dwarf goldenrod, a cultivar of the native plant, has been used successfully for weed control in the relatively harsh environment of traffic circles.
Goldenrod competes successfully with weeds in part because it is drought and salt tolerant, and also because it spreads rapidly. But it turns out that goldenrod also has another advantage: It is allelopathic. That is, it has the ability to release chemicals that suppress the growth of other plants. Another example of an allelopathic plant is crabgrass, which helps to explain why this plant is so difficult to eradicate.
There is a lot more information on this and other gardening-related topics at Cornell's Gardening Resources page.