thistle in flower beds - Knowledgebase Question

Elizabeth, Pe
Question by hhasak
February 23, 2011
Last year I battled thistle in several of my flower beds. Each time they appeared I would pull them out, some successfully & some not so much. I am afraid I'm going to kill the existing plants. I'm looking for some advice as to how not to have the same problem this year.


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Answer from NGA
February 23, 2011

0

Thistle is probably one of the worst weeds to try to control! Canada thistle, a perennial, multiplies both by seed and through spreading horizontal roots called rhizomes. Most other thistles, such as bull and musk thistles, are biennials. Their first year, they produce 4- to 18-inch-wide rosettes, but must first go through a cold winter period before they flower, set seed and die the following season. Unlike Canada thistle, these biennials can be knocked out by keeping them from setting seed. As long as you keep cutting them down when they appear, the roots will eventually run out of stored energy and the entire root system will die out. 2,4-D is widely used for thistle control, but one application is seldom enough to kill the plants. I think the best time to spray thistles is in the early fall, when temperatures are still in the 70s F. Nearly all of the plants will be in the rosette stage and actively growing. At this point in the season, the thistles are transporting sugars and starches to their roots for winter, and so more effectively carry the herbicide down along with these nutrients than in spring. Keep hacking and hoeing this spring and summer, and then spot treat with 2,4-D this fall. Best wishes with your landscape!

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