At What Point Is Young Whip Safe From Freezes?

I have a prune plum that was grafted in April that has not put on sizeable growth. It has grown about 16 inches and is only 1/8 - 3/16 inch in diameter. Most of the growth occurred slowly after late July. Should I put it into a pot and bring it indoors, or will it be safe during very low temperatures?

What are “very low temperatures”?. Some of us, 30f is low, others it’s -30f. I would also need to know what type of plum, and if you are zone pushing with that variety. What type of protection does it currently have? Right now I’ve got 250 grafted trees out in a nursery bed with no added winter protection, because I know that they are supposed to be hardy varieties, and if they aren’t, well I won’t have to waste my time on them, and I’ll regraft overt to something that is a hardy variety.

Perhaps down to -10f, though that is very rare. 10-20f is not uncommon. Its a petite d augen. Right now there is no protection. The root stock is only buried in the ground this past spring and the growth is a thin stick.

I wouldn’t worry. Keep it outside.