Throughout the fall season, garden centers are filled with a beautiful selection of mums (short for chrysanthemums). It is a wonderful time to plant these attractive, fall blooming plants, but some consideration should be given when planting in fall. Many folks plant mums and don’t actually do much to encourage flowering, but there are some measures you can take earlier in the season that will result in additional beauty at bloom time.
Mums are photoperiodic which means they respond to changing day length in the fall. So, when our days begin to shorten in fall that is their cue to start flowering. “Short-day” plants, like mums, flower when day length is less than 12 hours and some varieties have been developed to flower earlier or later in fall based on their genetics. This is typically identified on plants for sale in garden centers, with wording like “early season” or “late season”. You can often tell the late season mums as they will not have showy flowers yet. Don’t be afraid to purchase those plants. You can see all the flower buds waiting to burst once the days are short enough to trigger plant response. Why not enjoy the entire bloom at in your home garden as opposed to purchasing a plant that has reached full bloom at the garden center?
Mums are typically perennial in our area, although some colder winters may kill them. Most planting guides recommended spring planting for mums if you would like them remain in your garden as perennials. However, fall planting is the common practice since plants are readily available and often have showy flowers at that time. Mums die in winter because that their shallow, fibrous roots system may get frozen as the upper soil layers freeze and thaw over winter. When mums are planted in fall, their root system may still be fairly small when winter sets in, as opposed to spring-planted mums which have an entire growing season to develop a larger root system.
To ensure the winter survival mums, there are several considerations to follow when planting in spring or fall. First, and most importantly, you must select the right site in your garden. Mums prefer well-drained soil, so don’t plant them areas with poor drainage or occasional standing water. They also prefer full sun (greater than 6 hours of sunlight per day), which is needed for plants to thrive and produce large, extensive roots that can survive winter stress. If you have a more protected spot that is, closer to you home, south-facing and more protected from wind, mums will do better there. Avoid planting mums near outdoor lights as it may confuse day length and inhibit flower formation.
Mulching can greatly reduce winter stresses as well. Plan to mulch your mums at the end of fall as blooming begins to wane. Mulch them with wood chips or straw to a depth of about 4 inches. Leaves are not the best mulch as they tend to flatten and stick together over time, offering less insulation. Many mum growers will recommend cutting them back as the end of the season, but research has shown that mums survive better if old growth is left standing for the winter season with adequate mulch.
Once you have successfully established mums, greater blooms can be encouraged by pruning them early in the growing season. When mums reach about 4 inches of growth in spring, prune off the growing tips of all stems with shears or simply pinch them off with your fingers. This encourage lateral growth which will result in a shorter, but bushier plant. Prune the tips one or two more times before July when bud growth begins. The additional lateral growth, instead of leggy, upward growth, will result in a multitude of blooms when the fall days shorten.