Chrysanthemums are the quintessential fall blooming plant that are sold in hundreds of stores of all kinds, all over the region. They are prized for their beautiful display of flowers that add so much color to our landscapes, decks and patios each autumn. They are a favorite of gardeners everywhere and have commonly become known as simply mums, which certainly has a nice homey sounding name. But not all mums are created equal! You need to shop carefully if you want plants that will look good this fall and also come back in future years and bloom before a hard freeze puts an end to their floral display in the fall.
Chrysanthemums, like many fall-blooming plants are photoperiodic, meaning that they develop flower buds in response to the length of the night. As day light hours get shorter and shorter in late summer, the length of the night period increases. Once the nights get long enough, the flower initiation process begins. The earliest varieties of the hardy garden mums that we can grow only need 7-9 weeks of long nights to come into flower. Later flowering varieties might need 10-16 weeks of long nights, which means that most of these will probably not flower before we have a heavy frost which will damage the flower buds and prevent them from flowering. The early flowering types, like the ‘Mammoth Pink’ that was developed at the University of MN may start flowering as early as mid-August, which will allow us to enjoy their flowers for four weeks or more.
There are many different varieties of garden mums with varied flower forms ranging from the double flowered cushion mums, to the single daisy types, the larger decoratives, pompons, down to the button mums with their small double flowers. All of these plants will likely already be blooming if you buy them in the fall of the year. But you have to be careful to select varieties that are going to be hardy enough to survive our winters and also bloom early enough so that they bloom a few weeks before our typical first freeze. I recommend that you seek out your local garden center or greenhouse to better assure that the plants you buy are good ones for our area. The big box discount stores get their mum plants from a variety of sources, some of which might be from more southern locations that prefer to grow later flowering varieties of mums. So while these might look great when you buy them this year, you may never get to see them flower again in your garden if they are not well adapted to our climate.
Mums should be grown in full sun and in a well-drained soil. They can be planted in the fall, when you see them for sale or they can be planted in the spring too. Spring is also a good time to divide large plants and share them with your friends. Keep in mind that some of these plants can grow quite large. The Mammoth mums from Minnesota are aptly named because a single plant can grow to produce a mass of flowers 3’ in diameter. After the flowers and plants freeze, you can either let the plant alone for the winter or you can cut back the old flower stems and pile them over the top of the plant to provide some winter mulch. You may want to add some additional mulch after the ground has frozen to protect the small buds that have already formed at the base of the plant. Those buds will grow out to produce the stems for next year. Some people will also shear the tops of their mums in mid-summer to encourage more branching and more flowers later. But, do not shear them after August 1st or you can interfere with the floral initiation process and end up with fewer flowers then if you had not sheared them at all.