What happened to my 2 mums in planters?

Not sure if you left them in the pots or planted them in the ground, however, if you bought them this fall at a discount store, grocery store or somewhere similar, I am not surprised. Those mums are usually not hardy and are mostly in their prime when you buy them. They look good for about 2 weeks and that's pretty much all you're gonna get out of them. Doesn't matter if they are big or small or cost 15$ or 1$. I have found, if I buy them as early as they show up in the stores, the weather is good long enough for them to actually get some new growth and look decent through most of the season.

My best advice is to buy them at an established nursery, then you'll know what you're getting. :) If you did buy them at a nursery - take them back. They will stand by their products.

I agree with Jill, what you buy at walmart and lowes usually look great but they tend to not last. Buy the plants that are not in full bloom and buy earlier and they will acclimate and to well

I absolute agree with the earlier two. Never buy a mum in full bloom. Always try to find one listed as hardy. I know sometimes it is hard to tell what color your blooms will be, but pick a plant that has extremely tight buds. This will usually give you the best luck.

Did you repot them? Generally those mums are rootbound and destined to perish. I repot or place in ground and they have generally flourished. Then care for as usual.

Once they bloom their job is is to make seeds. That's the reason we dead head flowers; to keep them blooming. You can cut them back to any green leaves there may be left to see if new growth happens or just leave them to see if they go to seed. Only spring will tell.

Thanks so much for all your helpful answers. Cheers to everyone.