Some member of the gourd family; melon, squash, or pumpkin. Regardless of its exact identity, not much point in putting it out this late in the season.

Something in the cucurbit family.

The main occupant of the pot is a yellow rose called golden showers that was started from the black pot roses at HD. It has canker and isn't doing well enough to move up from the 10 inch pot it is in. There is also small petunia besides the Columbine seedling. Here's a pic but hard to see what's going on with too many adjacent pot and plants. I know that's a lot for a tiny pot but I try to make the most of the small space and go by the root and foliage development for size and capacity afforded to any plant. Anyhow, I will let it be for a while till a positive ID. I have another one of this volunteer in a much larger clematis pot that also has a morning glory volunteer that is now beginning to bloom.

The precise id of your volunteer may not be possible, if at all, before the plant produces fruit. I would pull it out now, waiting is not worth the results.

As for the rose I would put it in a separate, bigger container with good soil, prune it hard in spring and see if it will be more happy then.

Windberry, there are two little twigs so nothing much to Prune unless it puts out decent growth from here on. I will probably pull out the melon soon.

How about from a bloom, the ID?

Cucumber or cantaloupe are my 2 top guesses.

I think it could be a watermelon. That is the only cucurbit family member I ate and composted. I guess I may have to cut it's adventure short.

Let it grow, can't hurt much. At least it will give you something to watch late in season.

With the strange weather we've been having who know what winter will bring... if it even arrives. I'm all for an experiment, so I say let it grow.