I'd say go ahead and plant them (note that I'm not zone 5, though I have gardened for a bit in central Nebraska zone 5 for three years). Water, and maybe mulch a bit.

I wouldn't plant grasses this late.

Ideally they should be planted about a month before your first frost. If you do not think that is likely heal them into the ground in their pots for the winter and plant in spring.

Sorry Peren.all, I don't see heeling in as being sufficiently different than just planting them (with soil intact).

That way it's over and done with and you don't have to dig them up and possibly disturb root growth to replant them.

It makes a difference if they are warm season or cool season grasses. It is far more difficult to establish and winter over warm season grasses at this time of year than it is in spring. Once it is late enough for them to flower, their roots have pretty much shut down for the season and they often fail in the cold and damp.

So why would having a pot around their roots enhance their survival? I would think it would be a detriment in any way I can imagine.

Because potting soil is not the same as inground soil. As long as one can protect against freeze/thaw cycles and prevent the potted soil from freezing solid, the plant will survive. Unless the garden soil was exceptionally well draining or in a somewhat protected location (a raised veg garden bed comes to mind), I would not bury the pots in the ground but keep them somewhere else out of the weather and the cold.

Paying attention to the seasonality of the grasses will greatly increase one's success. The timing of proper planting times of cool season and warm season grasses was something I learned in my college hort OG class. And it is also a concept supported by the two OG gurus and authors Rick Darke and John Greenlee.

bbarron if she were asking about cool season grasses I would have said yes, go ahead and plant them. Healing in the warm season grasses works because you are not asking them to establish, you are putting them in a protected holding pattern until spring.