Question: Each fall, I purchase pots of blooming mums to add to my fall garden. They are supposed to be hardy, but many fail to survive the winter. What should I do?
Answer: The difficulty you are experiencing with overwintering these plants comes in good measure from the fact that they have spent the summer growing in containers and thus have a compact root ball.
While the plants can be transplanted into the soil without setback, there is not enough time for the roots to spread out into the surrounding soil. As a result, winter freezing, heaving and drying frequently lead to the plant's death. If you obtained individual rooted cuttings in the spring, the way the nurseries do, and raised these in the ground all summer, the plants would have a much better chance of survival.
The mums you have purchased are likely in the Prophet Series from Yoder Brothers, the world's largest producer of rooted chrysanthemum cuttings. Many of these have proven to be winter hardy in USDA Zone 5 if planted directly in the garden.
Your best chance with a potted hardy mum purchased in the fall is to plant it in the ground, mulch and water it well, and cut it back to 3 inches after the blooms are spent. After the ground freezes, apply a covering of conifer branches.
Next year you may wish to add some chrysanthemums to your garden in the spring. Many of the newer varieties, such as the My Favorite Mum series, are self-branching and need no pinching. But old-timers such as 'Sheffield', a late-blooming, apricot-pink chrysanthemum, should be included as well.
As for those fall-purchased plants, you can use them for seasonal spots of color and consider them annuals.
This post is excerpted from the September/October 2002 issue of Horticulture.
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