Hardy garden mums last in winter for the full cold season and come back in spring. You need to plant the right type and protect them well. These mums thrive in USDA Zones 5a through 9b with a good layer of mulch. Florist mums from the grocery store won't make it through the first hard freeze.
My own garden gave me a clear side-by-side test. I planted a row of garden mums along my fence in early June three years ago. When I first covered them with straw mulch in November, I wasn't sure it would work. Every single plant came back in April. That same fall I tucked four blooming store mums next to them with no mulch at all. None of those four made it. Same dirt, same winter, very different results.
The reason comes down to stolons. Hardy mums grow these stems under the soil that store energy for winter. Stolons act like a battery that powers your plant through the cold months. Florist mums skip this step. They pour all their energy into big flowers for the store shelf and build few or no stolons. Without stored energy below ground, they have nothing to draw on when your soil freezes.
Penn State Extension backs this up. They found that mums bought in fall while in full bloom often die over winter. The plant used its energy on flowers instead of roots. You should plant your mums in spring so they get a full season to grow strong below ground before the first frost hits.
Your mums winter survival depends on a simple mulch routine. After your ground freezes hard in late fall, spread 4 to 6 inches of straw or shredded leaves over each clump. This layer keeps your soil at a steady temperature. It stops the freeze-thaw cycles that push your plants out of the ground and kill the roots. Don't put mulch down too early or you trap moisture that causes rot.
Overwintering chrysanthemums also means you should leave the dead stems up. Those brown stalks look messy but they serve you well. They trap snow and hold your mulch in place. They mark where your mums sit so you don't step on them. Wait until you see new green shoots before you cut old stems to about an inch tall.
If you garden in the coldest zones, add extra layers for your mums. Place evergreen branches over the mulch or build a ring of chicken wire filled with leaves around each clump. These steps buffer your plants from bitter wind and deep freezes. With the right prep work in fall, your mums will push through the mulch each spring ready for another round of blooms.
Read the full article: Mum Flower: Types, Care, and Seasonal Tips
