Have you ever noticed that certain weeds are specific to certain beds in your garden? I just became aware this year that I've got several bed-specific weeds; weed species that appear only in one bed in my garden and nowhere else.
Take for example my oldest rose bed, a raised berm containing a number of old garden and shrub roses. This bed seems infested with bindweed, but yet bindweed appears nowhere else in my garden. If I don't watch the bed closely for two or three weeks, the next thing I know, a rose is being overtaken by the twining stems pictured at the right. I don't believe it's a coincidence that I imported this soil into my back yard while we were building the house and I thus suspect the bindweed seeds came with it, but how do I get rid of it now? Ten years of diligent cutting of the vines before they could set seed have not decreased the sneaky little ones that start in the periphery of a rose and stay invisible until they hit the sun at the top and spread. And you learn the funniest bits of information by doing research. I hadn't noticed that bindweed winds anti-clockwise until I read about it. Another bit of quick research tells me that seeds were still over 50% viable at 39 years. So maybe 50 years of pulling bindweed to go?
Another bed, again with imported soil, had an interesting vine spring up at one end of the bed that I first thought from appearance was going to be a melon of some sort. I let it grow that first year, turning nervous only when it began leaping from shrub to shrub and threatened to cover the entire bed. Finally, when it didn't produce any fruit from all its small white flowers, I chopped it down and have resolved to wipe it out of that bed as well. It also is still coming up annually, just in that one area. If it was the soil in the bed, why isn't it appearing in the rest of the bed?
I have Virginia Creeper that only appears on the front left of the house, Black-eyed Susans that only appear in my back rose bed, and a curious little nightshade-like weed that has a habit of appearing only in north foundation bed of the house. I'm betting the presence of the latter weed has something to do with the shade that is present there and nowhere else in my landscape. I will always encourage the Black-eyed Susans wherever they pop up, but I'd really like to see the rest of these creatures kick their habits.