Connecticut Garden Journal: Chrysanthemums
Fall is for mums. Chrysanthemums adorn front porches, window boxes and containers from September until frost, providing beauty and color that compliments our fall foliage. But this traditional fall plant can be more than a short-lived decoration.
Chrysanthemums can be perennials, but is depends on which ones you buy. Garden or hardy mums are varieties, such as Sheffield Pink, Mary Stoker and Homecoming, that send out extensive root systems and are hardy to zone 5. They can survive a Connecticut winter. Florist mums are varieties mostly grown in containers as annuals. They aren't reliably hardy.
If you want to grow a perennial chrysanthemum, purchase hardy, named varieties and plant them in the ground in full sun on well-drained soil. Container plants should be moved to a protected spot in winter. Plant mums at least 6 weeks before your first killing frost in fall. That's usually early- to mid-September, depending on your location. Leave the foliage on the plant after frost so it can catch blowing snow for winter protection. You can also cut it back to the ground and pile bark mulch on the plant to protect the roots.
In spring, remove the mulch, fertilize with compost and keep the shallow rooted plants, well watered all summer. To produce those full, rounded plants you buy at garden centers, pinch the growth point of the mum stems in spring when they're 4 to 6 inches long. Pinch two to three times in spring and summer when the stems reach 6 inches long. Stop pinching in early July. Otherwise, they will grow tall and lanky stems, more like an aster.