More than 3 million acres are infested with invasive plants in South Dakota. While this may seem on the surface like a strictly ecological problem, these weeds result in losses of more than $100 million every year*. Invasive plants in South Dakota outcompete native plants, degrade wildlife habitat, reduce crop and livestock production, negatively impact outdoor recreation, and more. If they continue spreading unchecked, these problems will only increase. Unfortunately, many invasive plants can still be found in public and private gardens (e.g., your own backyard!) and even for sale at garden centers and nurseries.
The good news is, you can help! By learning to identify some of the worst and most common invasive plants in South Dakota, you can be prepared to take action when you see one.
Invasive Plants In South Dakota
The following list includes identifying characteristics of some of the most problematic invasive plants in the state, as well as suggested native alternatives for each. If you find any on your property, look up proper techniques for removing that specific species, or contact your local Extension office for help. And when you see an invasive plant for sale, politely ask the seller to stop offering it, and explain why.
1. Absinth wormwood (Artemisia absinthium)
Also called sage wormwood, absinth wormwood has ferny, gray-green leaves with a strong sage-like fragrance. This heavily branched perennial grows two to three feet tall, and the stems are covered in gray hairs. In late summer, small, pale yellow flowers bloom in upright panicles.
White sage (A. ludoviciana) is a native cousin of absinth wormwood, and gray goldenrod (Solidago nemoralis) also features hairy gray stems and yellow flowers, with a similar height.
2. Canada thistle (Cirsium arvensis)
The confusingly named Canada thistle actually originated from Eurasia and North Africa. Growing up to five feet tall, it has even deeper roots, making it difficult to dig up. This creeping perennial has very spiny leaves with crinkly margins, and the slender stems branch only near the top. Purplish-pink tufted flowers bloom in summer, followed by tufted seeds on female plants.
Plant a native thistle instead, like fragrant thistle (C. pumilum), or choose another pink wildflower, such as prairie milkweed (Asclepias sullivantii).
3. Common tansy (Tanacetum vulgare)
Common tansy is a one- to three-foot-tall rhizomatic perennial that produces flat clusters of bright yellow, button-like flowers. Its compound leaves with toothed leaflets provide an attractive backdrop to the vibrant blooms. The smooth stems give off an unpleasant odor.
Native stiff tickseed (Coreopsis palmata) has feathery foliage and bright yellow blossoms, while pearly everlasting (Anaphalis margaritacea) features white button-like flower clusters.
4. Hoary cress (Cardaria draba)
Another creeping perennial, hoary cress grows up to two feet tall and branches only toward the top. While the lower leaves have a tapered, spatula shape, the upper leaves clasp the stem. Both have wavy margins. Tiny, white, four-petalled flowers bloom in flat clusters from spring into midsummer.
Whorled milkweed (Asclepias verticillata) has a very similar habit and appearance, and common boneset (Eupatorium perfoliatum), though taller, also makes a nice alternative.
5. Leafy spurge (Euphorbia esula)
Leafy spurge grows one to three feet tall with very narrow, alternate leaves on smooth stems. It has small, yellowish-green flowers surrounded by larger yellowish-green bracts. The seeds, which mature as soon as a week after the first flower, explode from their three-celled capsules. When broken, the stems exude a milky sap that can irritate skin.
Native spurges include flowering spurge (E. corollata) and snow on the mountain (E. marginata).
6. Oxeye daisy (Leucanthemum vulgare)
With its sunny yellow disc and bright white ray of petals, oxeye daisy appears to be a beautiful wildflower but is unfortunately invasive in South Dakota. It grows one to three feet tall and may branch slightly toward the top. While the oblong to spatulate basal leaves have petioles, the smaller upper leaves attach directly to the smooth stem. All leaves are serrated, and the flower petals often have notched tips.
White heath aster (Symphyotrichum ericoides) has similar, if smaller, flowers, and there are many native fleabanes (Erigeron spp.), all with daisy-like flowers, to choose from.
7. Perennial sow thistle (Sonchus arvensis)
Perennial sow thistle has yellow, dandelion-like blossoms that bloom in a cluster at the top of the two- to five-foot-tall plant. The bracts and flower stalks are covered with gland-tipped hairs, and tufted seeds follow the flowers. The leaves range from nearly entire to deeply lobed, have mildly prickly margins, and clasp the stem, which is filled with a milky sap.
Similar natives include curlycup gumweed (Grindelia squarrosa) and narrowleaf hawkweed (Hieracium umbellatum).
8. Purple loosestrife (Lythrum salicaria)
In mid- to late summer, purple loosestrife sends up tall spikes of striking magenta to purple flowers. These blooms are followed by tan capsules full of miniscule seeds that, in addition to creeping rhizomes, allow the plant to spread aggressively. The linear leaves have no petiole and appear in an opposite or whorled arrangement.
Tall native plants with purple flower spikes include prairie blazing star (Liatris pycnostachya) and obedient plant (Physostegia virginiana).
9. Salt cedar (Tamarix spp.)
A perennial shrub or tree, salt cedar has flat, scale-like leaves closely resembling those of a cedar or juniper. Fingerlike clusters of white to pink flowers bloom in mid- to late summer, followed by dry capsules that split to release thousands of seeds. It grows up to 25 feet tall with slender, arching branches.
Plant eastern red cedar (Juniperus virginiana) for similar foliage or a flowering shrub like false indigo (Amorpha fruticosa) for summer blooms.
10. St. John’s wort (Hypericum perforatum)
St. John’s wort is an erect, branched, herbaceous perennial growing one to three feet tall. Its bright yellow, five-petaled flowers bloom in terminal clusters in summer, followed by three-celled seed capsules. Both the flower petals and the opposite, oblong leaves have black dots along the margins.
Similar yellow wildflowers include flat-top goldentop (Euthamia graminifolia) and common sneezeweed (Helenium autumnale).
11. Yellow toadflax (Linaria vulgaris)
Also called butter and eggs, yellow toadflax has pale yellow snapdragon-like blossoms with golden orange throats. The flowers bloom in clusters in mid- to late summer above blue-green, threadlike foliage. Yellow toadflax grows one to two feet tall and spreads via creeping rhizomes and seeds.
Native golden monkey-flower (Mimulus guttatus) produces yellow snapdragon-like blooms, and four-point evening primrose (Oenothera rhombipetala) also has lovely yellow flower spikes.
Keep an eye out for these invasive plants and help protect South Dakota’s natural beauty! Which native plants will you grow instead?
*Statistics sourced from South Dakota State University Extension.
Plant These Native South Dakota Beautiful Instead
There are many beautiful native plants in South Dakota that you might consider for your home garden or landscape. A few of my favorites are red columbines, brown-eyed Susans, swamp milkweed, and more. They will thrive in your SD garden without much attention.
