Your pic is kind of fuzzy but it looks like the seed heads you're describing are along the stem. Yarrow makes umbrel flowers that raise above the plant, and are probably long gone in your/our zone, having bloomed earlier in the spring. But sorry, no suggestions what it might be. Do you think it's a wildling or something that came from seeds you had?

Pretty fuzzy picture - not sure about this but the foliage is remniscent of skeletonleaf bursage, Ambrosia tomentosa. It also has kind of a medicinal odor if brused. Need a better picture of the seed pods.
hortster

Ok, here's another photo. With the cooler weather, the stem is mainly seed heads and less green leaves.

And here's another.

Again, very suggestive of Ambrosia tomentosa. Have no idea if you should make tea from this...it's your health at risk...(or not?)!

Eat nothing that you are not 100% sure of.

hortster

I'd agree it's an Artemisia. Definitely not yarrow.