“I have trouble controlling weeds in my garden. Is there a difference between a weed and a garden plant?
—Benjamin Warren, Village of Elk Grove
Chicago Botanic Garden staff are also dealing with a heavy weed population this spring. As soon as they are pulled, other weeds seem to appear. Lots of wet weather meant little time to tend to weeds while promoting strong weed growth.
I define a weed as a plant that grows where it is not wanted in the garden. Different gardeners have different ideas of what constitutes a weed. For example, violets in the lawn are considered weeds by some gardeners and nice seasonal color accents by others. Dandelions are widely recognized as weeds; however, their peak bloom time in early spring is when many bees and other pollinators emerge and use dandelion flowers as a food source.
There is a biological difference between a weed plant and an invasive plant. Weeds spread easily, especially in disturbed areas, but generally do not pose a threat to the integrity of native plant communities. Invasive plants are generally non-native and can become established within existing native plant communities.
Invasive plants pose a threat to the integrity of the plant community. When invasive plants are introduced to a new location, intentionally or accidentally, they can spread prolifically, outcompete native species for resources, and ultimately even dominate the landscape. Buckthorn is an example of an invasive plant in the Chicago area that requires ongoing management for native communities to thrive. Buckthorn is also a common weed in home gardens, and I regularly pull it out of my garden.
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 advice on invasive plants. The Chicago Botanic Garden has an invasive plant policy which can be viewed at chicagobotanic.org. The policy can provide guidance to help you avoid choosing an invasive plant for your garden. You may come across plants for sale that are considered invasive in native plant communities.
Droplet (Podagrarian Aegopodium) is a formidable invader in many home gardens, and it makes me cringe when I see it. You can dig it up multiple times and it will reappear and grow into clumps of perennials and spread to other areas when dividing and transplanting. I’ve sprayed patches of it in my garden with herbicide four times in the last year and it always comes back.
This weed requires sustained management over a long period of time to be controlled.
the Star of Bethlehem (Ornithogalum umbellatum) is another common plant pest in home gardens. The best control is to dig it up carefully, making sure to remove the bulbs underground or it will continue to regrow. The Star of Bethlehem in my garden is starting to show white flowers now. This plant has also settled on my lawn. The plant will go dormant and disappear in the summer.
Garlic mustard (stalked alliaria) is another invasive weed that is blooming now. Its leaves are rounder and form rosettes at ground level during its first year of growth. The leaves send up a flowering stalk and become more triangular and heart-shaped with toothed edges. The small white flowers have four petals.
Remove flowering plants and place them in plastic trash bags to prevent the seeds from spreading. Prioritize your time to extract blooming garlic mustard to save labor in future.
Watch for buckthorn, mulberry and boxelder seedlings in your borders, as they are easy to uproot when seedlings. One of the best times to weed is when the soil is moist to bring out more roots.
For more plant advice, contact the Chicago Botanic Garden’s Plant Information Service at [email protected]. Tim Johnson is senior director of horticulture at the Chicago Botanic Garden.