I like to wait until I'm positive of what it is. I've ripped out so many perennials thinking they were left over annuals, that I don't take chances anymore. Garden Hibiscus looks dead every spring, and then they finally send up shoots.

I have left a plant amongst other plants until it has bloomed just to be sure if it was actually a wanted plant (though not in the right place). If it is wanted it can be transplanted. If it turns out to be a something I don't care about or a weed it gets removed. Other times I have transplanted it when it was quite small and grown out in a container or a holding bed. If the plant is actually growing right next to or inside another plant it should be removed and either discarded or transplanted.

I have gotten pretty good at recognizing the weeds in our area. There are many seeds I am sowing that are new to me and some seedlings look like weeds. Also with plunk and run I am sometimes surprised where a new wanted plant is going to appear.

Knowing the plant that is "dead" is important because some plants are very slow to come back in the spring. If it is an annual pull away. If it is a perennial and you are not sure, wait. If all the others of the same perennial have new growth the dead one is most likely dead and can be removed.