Don't cut back the top growth until spring when you see signs of green at the base. A couple inches of mulch around the base is okay, don't pile it higher than about two inches. If some don't come back next spring, check the website for Bluestone Perennials and find the mum of your dreams. Good luck!

Sounds like you have taken all the right steps. You could remove the flowers and buds right now if you want to take another precaution. Flowering and the subsequent seed-set saps an incredible amount of energy from the plant. Removing all the flowers this year will ensure that energy is, instead, directed toward building a stronger root system. PS--I'm interested in your comment about not mulching roses. I have never heard such a thing. Mulching the roses after the first hard freeze, and removing it in late winter, is the preferred method taught to Master Gardeners here, and is generally considered better plant management than using the Styrofoam cones. I'd be curious to hear more details about why it's not optimal, and what is recommended instead.

not all mums.. sold in fall .. are winter hardy ... though in your z6.. it should be more than the one i used to buy up here in in MI ...

if you are buying un-named plants at bigboxstore.. it can be hit or miss ... no matter what you do

so do you best... but dont go blaming yourself if they fail over winter ....

i would throw some mulch over them AFTER they are dormant... to forestall any mid winter breaking of dormancy.. should there be a failure of snow cover .... and a warm spell in mid winter ...

ken

If the plants are showing new growth at the base going into winter and you add a couple inches of mulch, they have a decent shot of overwintering.

Most times, mums are pushed into maximal bloom for late summer/fall sales, apparently are exhausted by the end of the season and doubtful winter survivors.

I would treat all late-planted mums as annuals and take even minimal overwintering as a plus.

By the way, it's probably not a good idea to place new plantings in a pure soil amendment product if the surrounding soil isn't good (i.e. dense and clayey). The planting spot will wind up being a moisture sink and the roots will likely stay in that spot without spreading out into surrounding soil, thus limiting hardiness.

I was told in another thread that mulching the base of roses can cause stem canker.

These mums were bought at a nursery and not a big box store, but they seem pretty standard to me.

I didn't know that about soil amendment... I just thought I was giving them the best possible soil to grow in. Well, I guess we'll find out in the spring if they make it! :)