Are Fall Mums Perennial?

As I prepared to give my annual fall talk on perennial garden maintenance, a customer snagged me with the following question: “All those beautiful mums outside,” she said, waving toward the side of the store, “are they perennial? Will these fall flowers come back next year?”

My answer was this: “Yes, depending on how you care for them.”

The used to be in the genus Chrysanthemum but these lovely plants have been reclassified as Dendranthema x grandiflora. No matter what the current botanical name, these are commonly called hardy mums or just chrysanthemums.

My customer isn’t alone in wondering if they are perennial, however. The term “hardy” for these plants indicates that they will last through several light frosts in the fall…it doesn’t refer to their ability to return next year. Here on Cape Cod, however, these chrysanthemums will live through the winter and return next spring if you pay attention to them this autumn. Here are the keys to successfully helping mums to come back:

* Be sure to water these well once a week, even after they finish flowering. Remember that they have a root system the size of the pot, and because the roots are tight and congested they will dry out quickly. Most people tend to forget watering once the flowers fade. If you want your plant to return, water deeply once a week well into December.

* Don’t cut the spent flowers and foliage down in the fall. Even when the flowers have turned brown and the leaves have wilted, leave the stalks in place until spring. Sometime in March or April you can cut them back and at that point you’ll see the new foliage emerging around the old stems.

* Be sure that the plants were planted in well-drained but organically amended soil. If you didn’t improve the soil before planting, spreading a 1″ layer of organic matter (at the store, we like Bumper Crop and Quoddy Blend Lobster Compost) around the plants, spreading it out at least 12″ beyond each plant. This will improve the soil from the top down.

* Once your mums come up next spring, mark on your calendar to shear the top 2 or 3 inches off of the tops of the plants in mid-May. This will help the plant be full and bushy next fall.