MALVA has my vote. Nice for two years, then look out. Its seedlings come up everywhere on every piece of un-mulched soil, ruining perennial beds with valuable specimens. If there's a Roundup poster plant, this is it!
You can sort of pull Malva though, no need for herbicide. Maybe you have to dig a little in tough ground. I nominate Euphorbia lathyrus as another nearly noxious self-seeder, though again pulls easily. Sorry no photo just now, but images can be found on line.
Karin, I've tried pulling Malva, and only a Hulk could get those out. They're so woody near the ground, there's no way. Tried digging a big with a pick to loosen root, well the roots seem to go in every direction and are as tough as concrete to get out. After I dug out most of the big ones, and then Roundup'd what I had missed, a couple of months later there are, I bet, a thousand tiny Malva seedlings growing all through junipers, asters, butterfly bushes, cotoneaster, echinacea, and poppies, 4 o'clocks, and at the edges of the thyme border. Even have some coming up in the yucca and grasses (rock border). I'll look up the Euphorbia lathyrus...just to see if I've got that!
I'm glad I don't have the Euphorbia lathyrus you referred to. Interestingly, the website mentioned ways to keep animals from decimating the owner's supply of the plant. One man's poison is another's staple...
My vote goes to Queen Anne's lace. My property suddenly, virtually overnight, became totally infested with this horrible weed. I have no idea where it came from. Probably birds or wind, although I had not noticed it around this area. I have resorted to the "cut off at the root as soon as possible" routine, but with about 1 1/2 acres or more of my property affected, this is a losing battle. In two years no progress has been made in irradicating this weed. I acquired a new weeding tool from Fiskars last year that is absolutely fantastic---for everything except QA's lace, that is. For some reason, that lovely taproot just slips on through, although nothing else does, including thistles. It is as if someone has greased the roots. Unfortunately, I have endangered and somewhat rare native species on my property that pretty much precludes the use of herbicides, which I do not want to use anyway.
Artemissia "Oriental Limelight", I put in three plants and they turned into a shrub like stature the next year, I thought it was beautiful, lovely variegated foliage. I'm big on foliage and was quite pleased, until the next spring they started sprouting up every where and I couldn't keep up with pulling them out. They spread underground and by the very next day there were more. I battled them all summer, needless to say momma plant is history! Janet
