Hmm) I had that idea too - to plant it in a container. I just couldn't afford the beast taking over my small yard, but I needed a lot of it for canning, so I took huge plastic tub, made holes in the bottom, placed it in the big rock in my natural hillside rock garden, filled it with some pot soil and planted my horseradish in it. It grew, but without any enthusiasm... So by the end of the summer, I decided to pull out tiny unhappy plants . To my surprise, it didn't come out of the loose soil... Under suspicion, I moved the tub. And yes, it was connected to the ground. The root from the plant found the hole, went through, spread under the tub(remember, it was on the rock!), found a crack in between of two big rocks... Now I have a horseradish plant right in the middle of my rock garden. Good thing though, it doesn't spread. Even spreading champion only able to fight that much with two huge rþcús). Now, I built a standalone HIGH bed (2.5') at the end of my yard and planted it there. So far, so good, second year in progress. What ever will make out of it(if any), I am going to kill by cutting. From my fighting experiences with Japanese knot weed I know nothing can grow, if you do not give a chance to the leaves to be above the ground for more then 1 day.

Yes - the OP's picture probably shows Lamiastrum galeobdolon (formerly Lamium), an invasive species. If your friend is lucky it could be Lamiastrum 'Hermanns pride' which is a controllable clumper, so I'd keep a very close eye on the foliage as it develops and compare with pictures. But be ready with the spade.

Thank you very much for the ID's. The first one is near the spot where I saw the bad-looking P. mugo subsp. rotunda about which I asked an ID too. At first I though they were both the same species because they looked similar, but when I went too look closer then I could see the cones were definitely different. Funny part is that someone else suggested in that thread where I asked for an ID that it could be P. thunbergii. So I guess both trees are similar looking indeed. The second one I think comes from a hedge close-by that was (I think) never trimmed and therefore started producing cones. The third one is almost a miracle to me. Closest Abies koreana that I'm aware of is at least a few hundred meters away from where I found it. I'm very glad I dug it out too because A. koreana was also on my wanted list. :)

Looks like Magnolia grandiflora to me. Not something I would expect to self sow in NJ, but what do I know. I'm from the south. Transplanting in fall or spring would be best, but you could do it now if you take an intact root ball and water well over the summer. It's small enough for that.