Looks like Stellaria media, Chickweed, to me.

Here is a link that might be useful: Google image results

Self-seeds like crazy. If limited amounts, remove & trash. If numerous, may want to consider herbicides.

Looks like chickweed to me too. But compared to my nightmare yours has not gotten filled out yet. Those "blooms" on the end will eventually branch out and make a big matted mess.

Maybe someone else can answer this for both of us.....but about month or so ago (7b) I reached down into gigantic clump of it to mash over to the side to spray...and was bombarded by hundreds of seeds shooting out at me (there's a term for that???).

Could not have been a good thing, I know!!!!

So wondering when exactly does it go to seed so if it gets ahead of me next year, I don't make same mistake pulling it up too late.

Next year, get it at these times:
1. as soon as you see it
2. while in bud
3. before buds open
4. at *first* indication of flowering

In other words: Remain alert!

Brit, the shooting seeds were probably bittercress. Chickweed and bittercress are both winter weeds that seed around this time. The best time to apply herbicides is in the fall. Then you will also get the small plants that are growing from all of those seeds.