The mums in my garden have been deliberately planted because of the colorful, cheery blooms they unveil in late summer and early fall. Even though they signify an end to summer, I love that they stick around through the up-and-down weather of autumn. All of my plants have come from planting the potted mums I bought for fall arrangements and then dug into the garden before winter. In this article, I’m going to talk about when to cut back mums during the growing season and whether you should prune them after the blooms fade in fall or wait until spring.
Hardy mums vs florist mums
You can find chrysanthemums at garden centers in the spring, but these late bloomers are most prevalent in displays and on shelves in late summer and early fall for autumn arrangements. Many varieties are hardy down to USDA zone 4 (-30°F to -20°F/-34°C to -28°C).
Chrysanthemums are considered “short day” plants, which respond to the longer nights and shorter days of late summer and early fall to bloom. This is called photoperiodism, which is a plant’s ability to detect to seasonal changes in day length and adapt accordingly.
Mums that are displayed outside, should be hardy mums, which have adapted to outdoor conditions. Check the plant tag to confirm preferred growing conditions. If you see potted mums indoors at a nursery or grocery store, they are likely what’s referred to as florist mums. In the case of these plants, a greenhouse has been used to mimic the short days required for the plants to bloom. Consequently, they have not been exposed to outdoor temperature fluctuations and it’s unlikely they would survive being planted outside.
What to do with your potted mum
Many folks treat even the hardy mums they buy in the fall as annuals, sending them to the compost once they’re ready to move on to a holiday arrangement. But I always try to plant mine in the garden. Or, if I don’t have space, I’ll plant it in an empty raised bed until I know what to do with it in the spring. I’ll dig it in and add a little bit of winter mulch (leaves or straw) around the base. I’ve had great luck with fall mums I’ve planted this way coming back in the spring. But it will depend on your climate and planting area (I tend to have some sheltered spots in the garden). I think it’s always worth a try if you were going to throw it out anyway.
Caring for mums throughout the growing season
Garden mums thrive in full sun areas of the garden with healthy soil and good drainage. (Though I will say there are a couple of stalwart plants in my dry, front yard garden. They thrive and bloom, despite the poor soil and dry conditions.)
Once you’ve confirmed your mum survived the winter, there’s not much you need to do throughout the growing season. I’ll give mine an occasional drink if there are periods of drought.
You can also give it a bit of organic, slow-release fertilizer when you’re feeding your other perennials. Adding fresh compost to the garden can also provide nutrients.
When to cut back mums to control the plant’s height
If you find that your mums flop over in the fall under the weight of their blooms, pinch them at least once or twice throughout the growing season. This will encourage more blooms, but also give the plant a shorter stature, so it’s less at risk of falling over.
Before cutting back your mums, wait until they’ve grown to roughly six to eight inches (15 to 20 cm) tall in spring. Take your pruners or sharp scissors and remove an inch or two (2.5 to 5 cm) of the stem. You can also use your thumb and index finger to pinch, like you would with deadheading. You can repeat this technique a couple more times into early summer (around early to mid July). Cutting back mums will encourage more new growth—lateral branching along the stems and hopefully more blooms.
Time your pinching to about three months before bloom time. This is important as some mums bloom earlier than others. If you don’t manage to give your mums a haircut, add plant supports once you see the flower buds start to form. This will prevent them from flopping when they bloom.
The blooms on both potted and garden-planted mums can be prolific, so deadheading can seem like an arduous task. If you see a lot of unopened buds, a few minutes with a pair of scissors can keep your plant looking fresh. Energy will be directed to those unopened blooms.
When to cut back mums after they’ve bloomed
Once the flowers and foliage have died back, the stems of a chrysanthemum will become quite brittle. If you’re planting a potted mum in the hopes it will survive the winter, it’s best to leave the foliage until spring as it acts as a protective barrier. Add some mulch around the base of the plant once the ground starts to freeze to protect the shallow root system. I live on a ravine, so fall leaves are put to work as mulch in all of my gardens.
Leaving the dead stems also helps you to see where the plants are in the spring in the garden. It can take awhile for signs of life. I’ll cut back my mums once I see little shoots of green leaves at the base of the old stems. That means new stems are on the way. You can use pruners or scissors, or even just gently snap the woody stems close to the base. But do be careful if you are cutting back this way by hand. Mums have very shallow root systems, so you could risk inadvertently pulling up the whole plant.
More pruning advice
Find tips on when to cut back: