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If you’ve driven along any interstates or highways in Illinois, there’s a good chance you’ve seen tall plants with spiky flower heads. Teasels have become an increasingly common sight across Illinois. While they may appear attractive, especially for cut flower arrangements, these troublesome plants can form large colonies that outcompete and choke out native plants.
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What is Good Growing?
Talking all things horticulture, ecology, and design.
Welcome to the Good Garden podcast. I am Ken Johnson, horticulture educator with the University of Illinois Extension, coming to you today from Jacksonville, Illinois with a Gardenbite. On this week's gardenbite, we're gonna talk about a plant that if you've driven along the interstates or highways here in Illinois, there's a good chance that you've encountered, and that is teasel. Teasel is becoming an increasingly common sight here in Illinois. So what exactly does this plant look like if you're not sure?
Ken Johnson:So here in Illinois, we have two species that we commonly find, cut leaf teasel and common teasel. And both of these species are gonna grow as a basal rosette, basically a a clump of leaves that grows low to the ground. The leaves are going to be puckered, with scalp edges for both species, and while they're growing as a rosette, they're going to develop a large taproot that can be over two feet long and an inch in diameter when it's kind of, quote unquote, fully grown. And we commonly describe teasel as a biennial plant. However, it's probably more accurate to call them a monocarpic perennial.
Ken Johnson:And these plants, these monocarpic perennials are plants that are going to produce fruit and seeds once, and then the plants are going to die. Whereas with a biennial, they produce this rosette the first year, and the second year, they flower. So this would be something like a carrots where we plant the seeds, we get the large root that we typically harvest. But if you would leave that carrot in the ground, that second year, they're gonna produce a flower, produce seeds, and that plant will die. Parsnip would be another example, of this.
Ken Johnson:And the reason it's probably more accurate to call them a monocarbolic perennial is because the size of the rosette is a better indication of when a tesla plant is going to flower rather than the age. So typically, when a a tiso plant, that rosette gets to be about 12 inches diameter, that's when they're going to start producing flowers typically. So it's more the size than the age of the plant that you're gonna use to predict when they're going to start flowering. Regardless of how long it takes diesel plants, to do this, when they've acquired enough energy, they're gonna produce a pretty large flower stock. It can be seven plus feet tall, and prickly.
Ken Johnson:They're gonna have spines and stuff along, that flower stock. Plants will also produce large prickly leaves along the stems of the plants as well. The stem leaves of common teasel are gonna be appear similar to the rosette leaves, but they're gonna be smaller. They're going to be opposite on that stem, and they're gonna have spines on the underside of the midrib, while cut leaf is going to have deeply lobed leaves and they will still have those spines on the underside of the midrib of the leaf as well. While the plants only flower once, each plant can't produce multiple flower heads.
Ken Johnson:Cut leaf diesels is usually going to produce white flowers, they're going to bloom typically from July through September, while as common teasel, it's typically going to produce purple flowers, and they're gonna bloom from June to October. And these flowers that are kind of small and clumped and dense oval shaped spiky heads, and a single plant is gonna be capable of producing thousands of seeds. After the seeds are produced, the stems are going to turn brown, and they may remain standing throughout the winter, which is which is when they really kind of pop out in the landscape, these dead stems standing there along the road sides. Teasel is going to grow in open sunny areas, and they can tolerate both wet and dry conditions. And while we can find them in kind of well established high quality habitats, we most commonly see them in disturbed areas like roadsides, areas where we've had a lot of construction, things like that, because they're gonna have this open area that these seeds really need to germinate.
Ken Johnson:So how did teasel get here? Teasel is native to Europe, Asia, and North Africa. And teasel was introduced into North America in the seventeen hundreds, and was used in the textile industry, and as an ornamental. So for hundreds of years, the seed heads of tislel have been used to raise the nap of cloth. Teasing was the common name, and this teasing helps bring loose fibers to the surface, and it kinda it can make cloth feel softer.
Ken Johnson:But we don't use tisel anymore in any kind of industrial production for this purpose anymore. The dried seed heads are also commonly used in flower arrangements, and it could be one reason why we often find these colonies around cemeteries, because of bouquets that people have put out at grave sites. And they also are commonly used in craft projects and things like that. Teasel is listed as an invasive species in Illinois through the Illinois Exotic Weed Act, which means it cannot legally be bought, sold, or distributed in Illinois. So despite being able to buy the seed heads online, legally, you can't do that in Illinois.
Ken Johnson:So like I mentioned earlier, teasels can outcompete a lot of our native plant species and they because they are aggressive plants, and cut leaf teasel is more aggressive, than common teasel. And they're gonna they can they're capable of rapidly spreading and outcompeting these native plants. The the thousands of seeds that these plants produce, can remain viable for at least two years in the soil, and this can lead to really dense patches of plants that make it difficult for other species to survive basically because they just choke everything else out. And the seeds typically don't disperse very far. About 98% of seeds are gonna germinate within 14 and a half feet of the parent plant.
Ken Johnson:But the plants growing along highways and interstates can be spread further by passing vehicles, you know, that wind going by, or by mowing equipment, depending on what times these plants are being mowed. As the the plants are being mowed and that's being discharged, that can spread at further distances. Seeds can also be spread by birds, and water. Seeds can survive a couple weeks, floating on water, so they can move that way in ditches, streams, rivers, etcetera. In addition to their prolific seed production, there's not a whole lot that feeds on teasel here in Illinois.
Ken Johnson:So once they get established, there's not much feeding on them and that just kind of perpetuates the problems that they cause. Fortunately, there are several things we can do to manage teasel if you have them in a landscape. So the rosette stage can be dug up from the ground. This is gonna be easier on smaller rosettes because the the taproot isn't going to be as large. So if you dig up the plants, try to remove as much of that taproot as possible, kinda like dandelions.
Ken Johnson:The more you can get out, the less likely that plant is to come back. When you have really large rosettes, when they have that two foot long taproot, it's gonna be difficult to get all of that taproot out. Once the plants begin to flower, the seed heads can be cut off and bagged, and the roots can be chopped one to two inches below the soil surface. If this is done, typically those plants aren't going to come back. If when you are cutting off that the flower head, make sure remove and dispose of flower heads.
Ken Johnson:Don't just drop them on the ground. Seeds will continue to develop even after that flower head has been cut off the plant. So get that out of there and dispose of it in in yard waste or something like that. Mowing teasel, unfortunately, is not a very effective way to management. The plants will still produce flowers even after repeated mowing.
Ken Johnson:They'll just produce very short flower socks there. And because these are growing as rosette, more than likely the the mower blades aren't going to hit those to begin with. And if you remove that flower head before it starts blooming, it's just going to send up a new one. So repeated cuttings, you're just going to get short flowers on those. Fire is not particularly effective either, and this can actually cause a flush of growth, from that seed bank that's in the soil.
Ken Johnson:Remember, they need open sunny conditions, and by burning, you've just created that, so a lot of these seeds that are sitting in the soil, all that vegetation has been removed, and you get a flush of growth from those seeds that are in the soil. Burning in the fall can help sometimes though, because it can help expose the rosettes that may be a little more difficult to see. And then you can go back with with an herbicide and target those rosettes. But burning alone isn't going to be very effective at managing teasel. You're gonna have to follow it up with herbicides or manual removal after you burn.
Ken Johnson:Tiesil can be managed using herbicides. So typically herbicides containing glyphosate two four d or trichlopyr can be applied to the plants in the rosette stage, this the spring, early summer, fall. It's going to be the rosette stage. The plants begin to flower, these herbicides become less effective and aren't very effective at all. So make sure you're targeting these plants in the the rosette stage.
Ken Johnson:Once they start flowering, you're better off cutting off those flower heads, bagging those up, and disposing of them. If you are going to use herbicides, make sure you read and follow all the label directions. That's all I've got for this week's Garden Mite. Hopefully, you've learned a little bit about teasel and how we can manage it in our landscapes. Good Growing podcast is a production of University of Illinois Extension.
Ken Johnson:Listeners, thank you for doing what you do best, and that is listening, or if you're watching us on YouTube watching. And as always, keep on growing.