Homegrown: Hardiness of Chrysanthemums

The following is from Iowa State University, Linn County Extension Master Gardener Intern, Jane Schildroth:

Several people have mentioned lately that they wonder if the new “mum” they picked up at the grocery store to have some quick fall color, will make it through the winter.  Unfortunately, there isn't a quick or simple answer to the question.

 There are two types of chrysanthemums available for most of the gardening public.  One type is the garden mum which produces underground stolons that make it possible for this type to survive from year to year.  The florist mum, on the other hand, does not produce these stolons and will easily be killed by winter here inIowa.  The response these plants have to short days and long nights makes the difference in their true “hardiness.”  Garden mums need approximately 5-7 weeks to flower after our short days begin and they can even survive several light frosts.  The florist mum, however, requires 8-14 weeks of short days before blooming and therefore doesn't usually have time for the buds to bloom before a killing frost hits the garden. 

 To complicate matters further, garden mums are often called “hardy mums” but even these cannot be counted on to make it through the winter.  There are some techniques to help their chances to survival, though.  Some of these can be done this fall and others next spring, which is the best time to plant mums.  If you buy a blooming garden mum in the spring, prune back the plants to one-third to one-half of their flowering height after the flowers are spent.  They will bloom again in the fall.  If you buy a garden mum in the fall, plant it as early as possible – remember they need 6 weeks – before a possible killing frost.  This gives the plants a chance to get established.

 Full sun and away from night or street lights is the preference of garden mums.  Avoiding light during the night makes sense for these plants because of their “photoperiodic” nature.  (That may not always be possible, but it's what the plants like best.)

 Another technique to improve the chances of winter survival is to avoid pruning the mums in the fall.  Leave the old foliage standing and snap it off during your spring clean-up.  And, most importantly, apply 4-6 inches of straw or pine needles in late November or early December when the surface of the soil has frozen.  This will help the soil stay more uniform in temperature and avoids the freeze and thaw process that is so hard on your mums.  Leaves aren't as good for mulching here because they pack solid when they get wet.

 There are many major types of chrysanthemums, several of which are hardy.  Go to

https://store.extension.iastate.edu/ItemDetail.aspx?ProductID=5711  to see an explanation of the various classifications.