Thorny Thistles
  Re: (0...)
Please somebody tell me how to get rid of these thorny thistles that pop up in the flowerbed. You pull or dig them out and in no time at all, they are back!
  Re: Thorny Thistles by Pippi (Please somebody tell...)
North Dakota State University has a nice writeup on thistles. However, some parts get a little technical, so I'll try to summarize a bit here.

Thistles are either biennial or perennial. The biennial varieties are easier to control. NDSU has some good pictures so you can try to identify what type you are dealing with. Biennial thistles germinate during the summer and fall, overwinter as a rosette of leaves, then grow, flower, set seed and die during the following year. They have a fairly short root system and only reproduce through seed. Your best bet to control biennial thistles is to prevent them from setting seed. Either cut back the stems before the flower buds are formed, or dig up or spray the rosettes in the fall or spring.

Perennial thistle is much harder to control. It reproduces through its seeds and its roots. Both seed production and the root system must be attacked in order to attempt to control these weeds. Unfortunately, perennial thistle roots can grow up to 10' deep into the soil and up to 15' laterally. Root pieces as small as 0.6" (about 2cm) can produce new shoots. Control methods indicated on the NDSU website included: Cut back/mow stems as close to the soil line as possible before flowering. Stems that are cut too high may resprout multiple stems from the remaining nodes. Also, regular tilling of the soil may help. The soil must be repeatedly tilled throughout the growing season each time the thistle growth approaches 3" (7.5cm) in height. This should eventually deplete the energy reserves in the root system if you are persistent.

Lastly, it seems like thistle seeds do not sprout well when they are crowded, so selecting a thickly growing grass seed for your lawn, or a thick layer of heavy mulch for your garden beds may help. Don't forget: even if you manage to control the plants you have now and prevent them from reseeding, there may be a large store of unsprouted seed still in your soil. This unsprouted seed can remain viable in the soil for over a decade, so no matter what, you'll need to plan for a long-term, persistent system of weed control.
Good luck!
The great thing about gardening is that you always get a chance to start over!

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