They naturally bloom as the days get shorter in the late summer. The period of darkness required to initiate blooming depends on the cultivar. By careful cultivar selection a garden could have blooming mums from August through October. Florist mums require a very long night so they do not set buds until late in the season and are often killed by frost before they ever have a chance to flower in the garden. Most outdoor mum varieties are now listed as garden mums and not hardy mums.
Cold tolerance is only one essential attribute for mums to live through the winter.
Mums are best planted in full sun in well-drained soil. One of the reasons mums fail to live through the winter is overly wet soils in fall and winter. Soil drainage can be improved by adding compost to the soil and planting in a slightly raised area. Mums are best planted in spring to assure better establishment and therefore winter survival. In spring mums are generally available as four inch pot plants, but they will grow quickly into sizable plants by fall.