How to Get Rid of Sow Thistle in My Yard

Overview

There are three forms of the tall, dandelionlike noxious weed called the sow thistle: Sonchus arvensis, or perennial sow thistle; Sonchus oleraceus, or annual sow thistle; and Sonchus asper, the spiny annual sow thistle. All three sport spiky serrated leaves in a dense basal rosette in spring which rises up to a bushy mass midsummer, topped by stems 1 to 5 feet tall bearing yellow composite flowers. Sow thistle eradication is a challenge requiring persistence in mechanical and chemical methods.

Step 1

Determine whether you have perennial or annual sow thistle in your yard. Examine the leaves of the plant: perennial sow thistle leaves are alternate and have toothed margins, while annual sow thistle leaves fully clasp the main stem, with either rounded or flat spiny lobes.

Step 2

Dig around one of the thistles to determine its root structure: Annual sow thistles have a single primary taproot, but perennial sow thistles spread by horizontal creeping root networks. Bring an exemplar to your local extension service office if you cannot determine whether you have an annual or perennial variety.

Step 3

Dig out annual thistle with a shovel in the spring before it flowers, as annual sow thistle spreads from seeds. Till the soil regularly to control annual sow thistle wherever possible to further prevent seeds and to discourage the seeds from germinating, as they require light to do so.

Step 4

Discourage perennial sow thistle expansion by pouring diluted white vinegar around the plant root area; perennial sow thistle thrives in an alkaline environment. Pour a teakettle full of boiling water on the plant each day before it flowers. Dig out each plant after it dies from the boiling water, and pour more diluted vinegar into the hole.

Step 5

Apply 2,4D or glyphosate-based herbicide at the maximum recommended rate to each plant before it flowers. Dig out the plant after it dies back, and pour another application of maximum strength herbicide into the hole to discourage the roots from resprouting. Repeat the process as necessary until the sow thistle is eradicated.

Tips and Warnings

  • Many people report irritations ranging from redness to a severe poison ivy-like rash from handling spiny sow thistle. It is uncertain whether this is due to physical scratches or from a chemical reaction. Always wear long pants, closed-toe shoes, a long-sleeved shirt, work gloves and eye protection when handling sow thistle or any other noxious weed.

Things You'll Need

  • Tiller or other mechanical cultivation device
  • Shovel
  • Work gloves
  • Vinegar
  • Boiling water
  • 2,4 D herbicide or glyphosate herbicide

References

  • N.C. State Turf Center: Spiny Sowthistle
  • Garden Organic UK: Prickly Sow-Thistle
  • U. Florida Nassau County Extension: Weeds

Who Can Help

  • Washington State Noxious Weed Control Board: Perennial Sow Thistle
  • North Dakota State University: Perennial Sow Thistle
  • Dow Agra Canada: Sow Thistle Biology and Control
Keywords: sowthistle eradication, sow thistle types, weed control, noxious weed

About this Author

Cindy Hill has practiced law since 1987 and maintained a career in freelance writing since 1978. Hill has won numerous fiction and poetry awards and has published widely in the field of law and politics. She is an adjunct instructor of ethics and communications.