It is hardy in Z6 but mulch is always a good idea for newly planted things with winter coming on.

Wet soil is a problem for this plant so I wouldn't mulch.

Cutting it down has removed the natural protection it would get from last year's growth.

It gets nice and dry in the summer where I’m planting it, it’s only been really wet because it has rained so much recently

Also, I wasn’t the one who cut it down, the garden center did

Wet soil over winter is likely to do it in. In Virginia clay I grow it on an embankment.

I planted four Kniphofia, pyromania 'Rocket's Red Glare' red hot pokers this summer, so I don’t know if they’ll survive winter yet. But what I’ve noticed is when I cut off the flowering stems, it leaves a sturdy tube behind. That’s where moisture must travel down to the base of the plant and cause them to rot when it gets wet and cold.

What I read said to gather the foliage and tie it up around it to give it cover. I don’t know yet if that’s good advice or what you should do if you don’t have foliage to pull up. Mine are planted on a steep incline on the sunny side of the yard. I wish us both good luck that they survive and thrive!

Ugh. I thought mine were carefree but perhaps ignorance has been bliss, and now they're going to hear they're borderline in my zone and kick the bucket this winter! One is even next to the gutter runoff and sits in wet soil all winter :(

Not a plant for fall planting and it should not have been cut back. Otherwise, if the soil drains well, zone 6 would be fine.