I'd pull them now. I think they spread by rhizomes, too? If so...they're spreading as I type, LOL! April

Thankfully no rhizomes -- it's an annual.

It also has nasty little spines on the stems, so this is now a no go plant. I'll keep one in the back by a blue cedar (and I'll weed that down each year) but all the rest come OUT. Yikes I was startled when I grabbed a stem to pull.

I'm all for natives, but not weedy spined ones. :)

CJ

LOL...
Last year I was surprised to find a Tansy (tanacetum vugare) growing....it is a toxic weed in cattle pasture, but since there are no cattle near by and just wheat fields I left it growing and harvested before it went to seed...I used the leaves to throw under cupbards,etc. to keep the mice away...no mice came in this fall from the field LOL!! I dug it up on sunday and moved it to my herb bed....pretty button yellow flowers but don't let this perennial go to seed...will spread by rhizomes too.

Vera