Cavinsco, I am going to take a guess that you seeing grass happily growing there in Portland right now, it may be quack grass.
Whereas you can lay down a blanket
of some kind of material to kill just about anything (as long as that blanket is deep enuf
), quack grass can be killed with contentious cultivation. It lays out horizontal rhizomes just below the soil surface. One thing, if you cover it with a mulch - it may just migrate
to where it can reach the surface, several feet away.
Still, those rhizomes are fairly shallow. Break them up and you will have new plants, everywhere!! What to do? I like using a spading fork and then get them completely out of the ground with a 4-prong cultivator.
I have seen a gardener go thru a bed to the depth of about 12" and shift all of that soil, pulling out the rhizomes as she went. That works but you don't need to go that deep. The roots are only down about 2 or 3 inches.
Don't try to bury them - that doesn't work. And, I once collected a black plastic garbage bag full and tossed it into the corner of the garden. It was a very shady corner or the sun's heat might have killed them. When I did this, DW said, "They aren't going to die."
her wrong, I left them all summer, all winter - for 12 long months! Remarkably, I was the person who was wrong. Those quack grass roots were still alive!
Okay, if your grass is something else - the spading fork/cultivator method may not work. As James says, "It depends some on what kind of grass."
We are each other's harvest; we are each other's business; we are each other's magnitude and bond. ~ Gwendolyn Brooks