It's a nutsedge, Cyperus species, and looks suspiciously like C. esculentus, aka yellow or flatleaf nutsedge, which is generally considered a weed in most places. A rather troublesome weed at that!!

Thanks! It figures I'd be nurturing weeds!

Pulling won't get rid of it, just leaves the little nuts in the ground to grow again.

That must be why I keep getting more of it. :o)

Ortho Sedge Killer. Can be used in the lawn, not sure about your other plants. Can also dig it out.

It's already gone to seed, so expect many more next year! Be ready next year to spray it with an appropriate spray.