I bought a raspberry bush and it has some vine-looking thing growing right out of the base of the raspberry plant. I followed the stem down into the dirt and I could swear it's coming out of the raspberry plant, so at first I thought thought nothing more and forgot about it (oops). But now that it's gotten bigger, it is obviously some impostor.
It's a weed, one of the Polygonums, commonly known as Knotweed https://en.m.wikipedia.org/wiki/Polygonum. Gonna be difficult to extract now its presumably got a large root system and mixed in with the raspberry roots, but if you can, pull it out.
Lady's Thumb or Persicaria maculosa same family but I've not had many troubles pulling this weed out. Is it as bad as the big knot weeds?
This weed is normal to find in a potted plant out of doors. In the nursery, this pot would be quickly turned on its side, given a big TWACK on the side of the pot, pull the entire plant, weed and soil out of the pot then pull and cut whatever is necessary to remove this weed.
Or more likely someone would see it and jerk it out, at least removing the top growth effectively starting the weed to be starved out. Plants in pots have roots that are easier to manage. Plants are very hardy and able to survive being twacked and their roots mangled (causes more root growth). I've never lost a single plant from the abuse of construction and the necessity for speed.
Your raspberry needs fertilizer. Basic NPK boxed fertilizer, less nitrogen than P and K or equal numbers (5-5-5 or 5-9-7). If you've not used potting soil, this would be a good time to change out that soil and remove that weed. Doesn't take much finesse or gentleness to do this job.
Do you see the dark spot in the center of the leaf? That is where a lady who had dirty gardening fingers smudged this plant dubbing it...Lady's Thumb. Seriously!!
It is common to find "WEEDS" or "volunteers" in containers. Some are extremely hardy especially if they've grown from a seed which germinated in the container. Depending on the volunteer, cutting the above soil growth often does not elimate the volunteer. As mentioned above whacking the container will loosen compacted soil. It will make it easier to remove the root ball. Again depending on the container size, cost, fragility of the plant, or how rare the specimen the general rule is to err on the side of caution: Take the container to a shaded, relatively dry area. Gently but firmly push on the sides of the container as you rotate it on its side. Gently and firmly pull the base of the plant from the container without breaking container plant stems. It's alive and can fail from shock. Using either your fingers to separate the roots of the two plants, or a cutting tool such as a hand spade or cutters. You'll find the tap root of the volunteer to be stronger than those of the container plant. (nursery grown container plants generally do not have tap roots) Separate and discard the volunteer. (unless the volunteer is a desirable plant you also want in your landscape. two plants for the price of one) Carefully repack your plant's roots. Minimize air pockets. it should be good to grow. Don't create anaerobic conditions by over watering.