Sonchus arvensis Perennial sowthistle.
Perennial sowthistle (Sonchus arvensis) is a South Dakota noxious weed that has become an obnoxious invader in my garden as well as in other gardens throughout the region. Like the spinier Canada thistle, this plant spreads by wind-blown seeds and underground, creeping rhizomes. It can grow to 7’ tall in a moist location and quickly take over. The plant has hollow, smooth, stems with dandelion-like leaves that are irregularly lobed, have spine tipped edges and contain a milky sap. The flowers also resemble those of a dandelion but they are borne on branched clusters atop the plants. The roots can grow down several feet with multiple plants arising from the roots and especially the wide-spreading rhizomes or underground stems. Consequently gardeners will often find colonies of these plants, often when they are in bloom or when their seed heads are mature and releasing their seed to the wind, thanks to a small cottony group of hairs attached to each seed.
|Young perennial sowthistle plant all ready to bloom.||Young perennial sowthistle plants with rhizomes.|
It can be difficult to control these pesky weeds for a number of reasons. First of all, they grow quickly, particularly in moist soils. They often are hidden from view until their bright yellow-orange flowers call attention to their presence. But by then, they are usually well-established plants with an extensive network of rhizomes. Hoeing or tilling can be an effective means of controlling young seedlings but older plants are more likely to just sprout up an equal or greater number of new plants from the chopped-up rhizomes. Herbicides may also be ineffective because of the glossy surface of the leaves which makes it difficult for the herbicides to be absorbed. Repeated mowing and pulling are often the best bet – anything to keep the plants from going to seed will be helpful.
For more information view More Perennial Sowthistle Showing Up This Year on iGrow.