Because container chrysanthemum blossoms are often the colors of fall leaves, it seems right they crowd garden store shelves in September and October. Mums (Chrysanthemum spp, or Dendranthema x grandiflora) -- in reds, yellows and oranges -- are often treated as fall annuals, brightening garden beds until they finish flowering. It is possible to keep these plants over winter so they bloom again. You'll need to act fact when you get them and go the extra mile.
Plant the Mums
One way you can try to coax the mums to come back in spring is to plant them in the garden and treat them as you would other spring-planted perennials. This only works if you buy them early in fall, not late in October, and live in U.S. Department of Agriculture plant hardiness zones 3 through 9.
Plant them early to allow the root systems the maximum time possible to grow and develop before winter. Set the mums in beds that have well-draining soil and plenty of sun, spacing them 2 feet apart. Water the mums enough so the soil remains moist at all times until the first winter freeze. After that, snip each stem to about 1 inch tall, remembering to sterilize the pruners first by soaking them in a mixture of equal amounts of water and rubbing alcohol. Tuck the plants in for the winter by covering them with a 4-inch layer of mulch, pine needles or straw to insulate the soil and keep temperatures more even.
Protect the Mums
The alternative, if you hope for new blooms on your mums the following year, is to leave the plants in their pots until the flowers wilt and the leaves turn brown. Then, get out the pruners, sterilize them, and do a major trim. Snip off everything, leaving only 1 inch of each stem.
After you finish cutting the plants back, find a spot outdoors that's sheltered from the wind. The shelter of a tree or wall makes a big difference for the mums during winter. You'll still meed to mulch -- layering on up to 8 inches of dried leaves or straw -- to keep the soil temperatures from fluctuating too much.
If you live in the colder regions of the country, even a sheltered spot outdoors might be too cold. Set the mums in the garage on a stack of newspapers and wrap more newspapers around them. An unheated basement works, too.
If you leave the pots outdoors, they don't need water. If you store them inside, check the moisture every week and water if the soil feels dry.
Look for Growth in Spring
There's no guarantee the mums will make it, but they might. You will know for certain in early spring if the plants start putting out new shoots around March.
When the green shoots appear, it's time to start caring for the plants again. Clip out the old stems with sterilized pruners to give the fresh, new ones room to grow. At the same time, start feeding the plants with liquid, all-purpose fertilizer. Add 7 drops of the fertilizer into every 1 quart of water, or according to label rates, and use the solution to water the mums.