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Invaders of the Weedy Kind

Written by Rhonda Ferree, retired horticulture educator

I have been battling some difficult and very invasive weeds this summer in my yard.

A new weed in my gardens this summer is prickly sida (Sida spinosa), also called prickly mallow. This summer annual has a yellow flower and prickles at the base of each leaf. So far it is mainly in my herb garden so I wonder if I brought the seed in on a new plant somehow.

The other relatively new weed on our property is black swallowwort (Cynanchum nigrum). Although in the milkweed family, this plant does not have a milky sap, nor is it eaten by monarch caterpillars. This is a perennial vining plant with dark-purple, egg-shaped leaves. Like other difficult to control perennial vines, it has rhizomes that sprout new plants.

For many years now we have been battling oriental bittersweet (Celastrus orbiculatus) and garlic mustard (Alliaria petiolate). Both plants seem to grow everywhere and spread very quickly.

Similar to black swallowwort, oriental bittersweet is a perennial vine that is difficult to control. Oriental bittersweet has more yellowish fruit than our less aggressive native American bittersweet, but seeds from both are dispersed by birds and animals. In my case, I have this aggressive oriental vine growing throughout my vinca groundcover, tangled within my shrubs, and lurking among various other flower beds. Once established, the plant also spreads quickly through underground root structures that send up new plants throughout the landscape.

My husband Mark has declared war against the garlic mustard on our property. He has been cutting, spraying, pulling, and mowing it. If you have this dreaded plant, then you know it is an aggressive invader of wooded areas where it can form dense stands. These plants choke out our native wildflowers and other woodland plants by shading other plants. Even worse, it releases allelopathic compounds that inhibit seed germination of other species.

Black swallowwort, oriental bittersweet, and garlic mustard are all invasive species of concern in Illinois. Because invasive plants are hardy and persistent, they can be difficult to control once established.

Learn more about these and other invasive plants of Illinois at Other plants listed there include bush honeysuckles, burning bush, Callery pear, and many more. The site also covers other invasive species in Illinois besides plants, such as Asian carp, emerald ash borer, wild boar, and zebra mussels.

Weeding is simply part of gardening, but can be a frustrating task. Nevertheless, weeding can also be therapeutic and satisfying as we watch a landscape bed change from a weedy mess to a beautiful display.



As horticulture educator, Rhonda Ferree inspired citizens in local communities to grow their own food and improve their home landscapes. She focused on high quality, impactful programs that taught homeowners how to create energy-efficient landscapes using sustainable practices that increase property values and help the environment.

After 30 years with University of Illinois Extension, Rhonda retired in 2018. She continues to share her passion for horticulture related topics as “Retro Rhonda” on social media.

ILRiverHort is a blog that helps people connect to nature and grow.