If you live in a non-temperate climate, like the band of Zone 5b and north, and would like to grow mums in containers, there are some mum care details you need to know. Mums in containers are difficult plants to overwinter, but it's not impossible. The first step is to start with a hardy variety. Then, follow these best practices to growing mums in containers.
Always repot a purchased mum plant. They are usually root-bound, meaning that the roots are taking up the majority of the pot. Replant the mums in a container larger than the one it came in so the roots have room to spread out and breathe. If the plant is root-bound, the roots will have formed a large tangle at the ends. Carefully pull the roots apart before repotting.
Mums thrive in well-drained soil. If you are growing mums in pots for a single season, you can plant mums with other plants in a large container. If you're attempting to overwinter the potted mums, plant them by themselves in a container, and try to plant them in the spring. This gives the roots time to grow and establish well before winter. Mums in flower beds don't usually face the issue of not having enough space, but mums in flower boxes or shallow pots may not have enough room to spread out.
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. If you're bringing mums inside for the winter, make sure they are by a window where they get the same amount of sun.
Water newly planted mums thoroughly, and never let them wilt. After they are established, give mums about an inch of water per week. When bottom leaves look limp or start to turn brown, water more often. Avoid soaking the foliage, which encourages disease. Make sure the water seeps into the soil to the roots, otherwise the plant can drown.
Plants set out in spring should get fertilizer once or twice a month until cooler weather sets in. Don't fertilize plants set out in fall as annuals, but plants you hope to overwinter should get high-phosphorus fertilizer to stimulate root growth.
Once the first hard frost hits, move your mums container inside or into your unheated garage. Mulch up to 4 inches with straw or shredded hardwood. Fill in around the entire plant, spreading well between branches. Cover the pot with cloth.
Pinch off dead blooms to clean up the plant, but leave branches intact—mums have a better chance of surviving if you wait until spring to prune old stems. As soon as the weather warms, pull away mulch to allow new shoots to pop up.