This is one that's hard to ID without the blooms. Did it bloom for you during the summer? If so, what did the blooms look like?

Things it could be:

Phalaris arundinacea var. picta
Gardener's Garters
Zone 4

Carex morrowii maybe 'Ice Dance'
Variegated Sedge
Zone 5

Liriope muscari variegata
Variegated Lilyturf
Zone 5

As you can see, you are at or near the bottom of the hardiness range for any of these plants.

In a container, you lose 2 zones, so your winter will be like zone 3 unless you bring the container inside, and a screened patio may not be sufficient protection.

I had a really close look at your picture & I would be willing to bet that it is Phlaris and I think it would be fine in your porch or ... if you like the look of it, you could always overwinter it indoors ....

I always tend to err on the side of caution & tend to agree with donn. I have always dug my pots of grass into the veggie garden over the winter. However, since moving north another 1.5 zones, I am finding that I am probably over-cautious. Many of the nurseries up here overwinter their perennial pots outdoors & above ground - yikes eh?.

Note: I still dig my potted hostas & grasses into the ground - then I don't worry about watering & I know that they will survive.
A.