According to the USDA, the lowest minimum temperature that planted mums can generally survive is right around 20 degrees Fahrenheit because the roots themselves are insulated by the earth.
Mums and Frost: How to Care for Mums When It's Cold
In general, potted perennials are two hardiness zones more tender than their stated rating for in-ground plants. This would make potted garden mums hardy only down to USDA zone 9, where the minimum average temperature is from 20 to 30 F.
Still, these wilted blooms might help protect your mums once the weather temperatures decrease. According to outdoor water maintenance specialists, Gilmour suggests using mulch to cover the base of your mums when the temperatures reach 20°F—this can help get the soil at an even temperature through insulation.
“You can move the plant to a cold frame or greenhouse structure. You can also keep the plant in the corner of an unheated basement or insulated garage where it will not freeze.” With a little preparation and care, your hardy mums will reward you with their stunning displays of color every fall.
If you want to keep a mum as a houseplant, deadhead it and bring it in before freezing temperatures arrive. Monitoring soil moisture levels is critical in keeping mums alive over winter.
Instead, you can try letting the plants go dormant in their pots and keeping them in a cold but frost-free indoor spot like a garage until the following spring. Then you can plant the mums outside in your garden once the soil has warmed up.
Mums fall into two main camps: florist mums and garden mums. Florist mums are the compact, potted superstars you see at nurseries and generally do not return each year. Garden mums grow in a looser habit and reliably return year after year. Both types are part of the same species, Chrysanthemum morifolium.
If your mums are in pots, make plans to overwinter the pots in your garage. After the first frost (not hard freeze), cut back plants as indicated above. Cover the mums with 3” of mulch, cover the pot with an old sheet and move into a cool garage.
The chrysanthemum lifespan is only three to four years and while it could last longer than that, it will get more susceptible to winter damage with each passing year.
Mums grow best in full sun.
They're at their best when they get six to eight hours of direct light. Give them too little sunlight, and you'll get a weak plant that produces few flowers. So choose your mum-planting place wisely.
Mums are hardy blossoms that can withstand colder temperatures – down to 20° Fahrenheit – but prefer the 60-70° Fahrenheit range. They don't do well in hotter summer temperatures though – anything over 90° Fahrenheit.
Winter pansies go dormant after temperatures drop to 25°F but will survive to 20°F. These winter plants are cold-hardy, but adding a layer of mulch—sure as light pine straw—over the roots will help the plant retain moisture and reduce damage during a hard freeze.
Chen doesn't recommend planting potted mums in the ground. As well as not being good with the cold, she says they tend to become tall and leggy before blooming. However, if you are going to give it a try, she recommends cutting the plant back to two-thirds the size before planting and fertilizing regularly.
Mums planted in the ground won't dry out as quickly and may only need watering once a week. Plants in containers may need watering every other day or daily. In either case, work your finger into the soil under the mum. If the soil feels dry below the surface, it's time to water.
Three Ways to Overwinter Mums in Pots
Keep in mind that the ultimate goal in overwintering your mums in containers is to keep each plants' roots and stems from feeling harsh freezing temperatures. Nice and cozy, is the plan. Also, winter care includes deadheading them back BEFORE storing them for winter.
General Mums Care
If a frost is expected, move the mums to a protected inside area such as a garage, shed, or barn in the evening, before the temperature drops.
Florist mums are best left in pots and/or indoors because they have weaker roots that produce few underground runners. If planted outdoors, florist mums will act as annual plants because they typically can not survive the winter.
If you want to overwinter your mums indoors, then place them in pots (with as much of the roots as you can get) after the first sign of frost. Store them in a completely dark place and keep their soil moist. In the spring, gradually allow them to get acclimated to the light and replant them outdoors.
Throughout the winter your plant is still going to need some water. If the soil gets completely dry, the plant can die of desiccation. While regular watering isn't necessary, monitor the moisture level and water if the soil is dry.
Whether in a pot or your garden, mums like lots of light. Choose a full sun spot that gets at least six hours of light a day. Plants that don't get enough sunlight will be tall and leggy and produce fewer, smaller flowers.
Mums (Chrysanthemum spp.).
Considered mildly toxic to dogs, cats, and horses, mums are by far one of the most popular fall flowers. If consumed, you may see vomiting, diarrhea, hypersalivation, incoordination, and dermatitis in these animals.
For any mum in the garden, mulching can help it to survive the first winter as well as succeeding winters. Cut back the tops of plants after leaves have turned brown each fall. Use several inches of a loose, airy mulch that will allow light to get to the small side shoots throughout the winter.