1. Ignoring the Type of Mum
Amy Enfield, a horticulturist for Miracle-Gro, says garden mums should be planted outdoors by late summer or early fall so the roots have time to form before the soil freezes. Also known as hardy or Belgian mums, garden mums are sold in garden centers and nurseries. They’re perennials in USDA Zones 5 to 9. But even when they’re planted at the right time, they need a few other things, like excellent drainage. Enfield adds, “There’s no guarantee they will survive the winter, particularly the further north you live in the U.S.” Enfield explains that florist mums, the kind sold in the houseplant section of your local grocery store, aren’t meant to transplant at all. “Unlike garden mums, these are meant to grow inside as indoor potted plants and are not cold hardy.”
2. Planting in Too Much Shade
Cynthia Drumgool, a potted plants and mums manager with Ball Horticultural, says garden mums need full sun or at least partial sun. One exception: in very hot climates, mums benefit from a bit of shade during the hottest part of the day. Otherwise, give them plenty of sun for plenty of blooms.
3. Over-fertilizing Your Plants
You can give your plants fertilizer with nitrogen when they’re starting to grow leaves and branches in spring. But don’t fertilize once your mums form flower buds, says Enfield. Fall mums will benefit from a high-phosphorus fertilizer that promotes root development.
4. Forgetting to Water Mums
Enfield says that one of the biggest mistakes you can make with fall-planted mums is failing to water them. “Days are cooler, the sun isn’t as intense, so plants, even those in containers, don’t dry out as quickly. However, plants will continue to require water until the ground freezes.” While you may need to water daily in the summertime, water only when the top inch of soil feels dry to the touch after the weather cools down. Do the same for potted indoor mums.
5. Cutting Garden Mums Back Too Soon
Enfield advises that you deadhead your garden mums in the fall but leave the rest of the plant alone for as long as possible. Fall mums use their leaves to turn sunlight into energy for forming roots. Wait until the following spring to do any additional pruning or until the stems die back to the ground. Then, cut the stems down to about an inch above the ground before new growth appears.
6. Pinching Mums Too Late (or Not at All)
If you don’t pinch the growing tips of your garden mums, they’ll bloom, but you’ll have plants with long stems and fewer flowers. “Pinching to remove flower buds helps encourage the plant to branch and become fuller,” Enfield says. “Stop pinching in early July (no later than mid-July) and allow the buds to form and flower.”
7. Not Improving Drainage
Mums won’t thrive in soil that drains poorly and stays too soggy. That’s especially true in cold-winter areas, says Enfield. So if you have heavy clay or compacted soil, mix in some good-quality garden soil or compost to loosen it and improve the drainage in your planting site. Finally, Enfield says that the fall mums sold in garden centers nowadays aren’t the same kinds of plants sold 20 years ago. Although garden mums are considered hardy to Zone 5, breeders have developed fall mums with big mounds of showy flowers. This has resulted, she says, in plants that may not be as cold-hardy as in the past. So, if your fall-planted mums don’t come back like true perennials, just treat them as annuals. Replace them with beautiful, fresh plants when you’re ready to do your fall decorating and enjoy their colorful blooms for a season.
