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.
Depending on the weather, Labor Day weekend is a good indicator for when to move your potted mums outside and start planning your fall gardening and decorating. If it's still sweltering, you may want to wait a few weeks, putting your mums out in mid-to-late September.
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.
Maybe! It depends on when you plant them. If you plant them in the fall, that's often too late because they're putting energy into blooming, not building roots. You may get lucky if you plant them early in the fall and if you choose plants in tight bud, rather than plants in full bloom.
Your mums can even stay in the ground, provided that you give them enough mulch. Just be sure to cut off the dead stems and bury them in mulch shortly after the first frost.
Planting Mums
If you're using a mum as a perennial, plant in early spring or in the fall at least six weeks before the first killing frost. You'll find smaller plants for sale in the spring than you might in fall.
In most areas they won't need any extra winter protection, but in Zone 5 it's a good idea to put down a 2-4 inch layer of mulch around the plants. If you live in a colder region (Zones 4 and colder) or it's already October, your best bet is to overwinter your potted mums indoors in a cold, dark place.
Mums thrive in full sun conditions as long as you give them enough water. Choose a spot that gets at least six hours of sun a day. Plants that don't get enough sunlight will be tall and leggy and produce fewer, smaller flowers.
The perennial, fall-flowering form is Chrysanthemum x morifolium and the annual variety is Chrysanthemum multicaule. If your plant came without identification, note that the annuals have thinner, strappy leaves that are not as toothed as the perennials, which are wide and deeply notched.
Though technically perennials, mums are often grown as annuals. If you live where winter can be frigid (USDA Plant Hardiness Zones 3 through 6), go with early-blooming varieties — they're more likely to come back in subsequent years.
Potted mums won't survive outdoors in most areas when the weather gets cold. Plants that are growing in the ground can handle air temperatures below 20°F because the roots are insulated by the surrounding earth. But plants that are growing in containers don't have this protection.
Cover the plants at night when freeze warnings are in effect. To keep the plant attractive and healthy, snip off any dead blossoms as soon as they wilt. However, if you are in a cold climate, leaving the dead foliage on the plants has been found to help the plant survive colder temperatures better than pruned plants.
Planting during this season gives them plenty of time to establish roots in preparation for winter. You can also plant mums in the fall, at least six weeks before the first frost, and that could be in September or in October, depending on your location.
If you cut the mums back to the ground, fewer stems will grow next year. After this, when wintering mums, it is best to provide a heavy layer of mulch over the plant after the ground has frozen. The mulch for winterizing mums can be straw or leaves. This layer of mulch helps to keep the ground insulated.
Mums' roots are shallow, and they don't like competition. Plant them about 1 inch deeper than they were in the nursery pot, being careful with the roots as you spread them. Watering: Water new plants thoroughly, and take care not to let them wilt. When bottom leaves look wilted or start to turn brown, water more often.
Don't let your mums get too dry or wilt between waterings. Water your potted mums at least every other day. They like to get about 1 inch of water per week. Water at the soil level (the base of the plant) and not on top of the foliage.
Buy Mums Before They Are in Bloom
Our opinion is that the best time to buy fall mums is at the end of August/beginning of September before they are in full bloom.
There are potted florist mums, which look just like garden (hardy) mums and even share the same botanical name (Chrysanthemum x morifolium)—and they're perennials, but their survival depends on when you get them and where you live. Garden mums, also known as hardy mums, are perennial mums.
Overwinter Them Indoors
If you live in an area that receives frost, move your potted Mums into a protected place that will stay above freezing. You don't want the roots to freeze or they may die. You can put your plants into any cool and dark location, such as an unheated garage or shed.
Plant Mums in the Spring
Though they bloom in the fall, if you want healthy mums that return each fall, your best bet is to plant them in the spring. Doing so means they have time to establish their root system before flowering, says Myers.
If you love your pot mums and can't live without them, the best plan is to keep them in pots and keep them out of the rain. The perfect place for pot mums is on the covered porch, under an overhang or anywhere else you can keep them away from rain and soil.
I have used old pillow cases, sheets, towels and even cardboard boxes. Just be sure that whatever you use to cover your plant, the cover reaches the ground and traps the warm air inside the canopy. Plastic can be used but it is important to note that you should not let the plastic touch your plants.