Experts and BHG readers answer.
Hi, I'm so sorry it's taken so long to get back to you. Our service was down for a month for repairs. I'm sure by now, you've done something with your mums, but yes, you could plant them in the ground in the fall. Just understand that if you plant them really late in the season, they won't have much of a chance to develop a good root system into the ground so they may not overwinter. You can cover them with a loose mulch of leaves and, if it snows, cover them with snow as an insulator. Hopefully, they'll come back next year.