Matthew Stevens: Chrysanthemums are the star of the fall season

Autumn is approaching quickly, and one of the landscape plants we most commonly associate with the fall is the chrysanthemum, frequently referred to simply as mum. Fall flowers are often in short supply, compared to the relative abundance of blooms in spring and summer, and yet reliably year after year chrysanthemums are the shining star of fall landscapes with their late-arriving blossoms.

Chrysanthemums are short-day blooming plants, meaning their bloom is triggered by the shortening length of daylight and increased length of darkness that occurs each fall. They are members of the Asteraceae, or daisy, family, with flowers resembling the classic disk shape we associate with daisies. Many of the mums we buy and plant in the fall are herbaceous perennials, though gardeners treat them like annuals, ripping them out after the flowers have succumbed to frost.

Though there are several different types of chrysanthemums and thousands of cultivars, all of the mums we use in North Carolina like essentially the same conditions, preferring well-drained, high organic-matter soils in full sun. They will do OK in a small amount of shade, too, and an hour or two of late afternoon shade may even be a good idea, but more than that will reduce the amount of blooms you see. Mums do use a fair amount of water, particularly large container-grown mums, but they don’t like to be in wet soil, so adequate drainage is important.

If you’re planting mums this fall and want to overwinter them, you will need to do a bit of work in the spring and summer to duplicate the show you get in year one. Container-grown mums are pinched back repeatedly throughout the growing season in order to develop large, dome-shaped plant shapes, and they will need to be pinched back that same way in subsequent years in order to grow to the same size and shape the following year. Even the so-called hardy mum, which are treated more like traditional perennials, including cultivars like “Sheffield Pink” and “Mary Stoker,” should be pinched back for peak performance.

Use mums in your landscapes in containers or in the ground, in high-visibility areas like lining walkways, edging along the front of a border area or along a wall. They can also be used as companion plants with asters, ornamental kale and cabbage, and other plants that stand out in the fall. They can develop some leaf spot fungal diseases, but avoiding watering the foliage and instead directing water to the root area of the plants will lessen those issues.

Mums have relatively low toxicity, but there is an oil in the leaves and flowers that can cause redness and irritation in some individuals sensitive to the compound.

There is also a natural insecticide made from an extract from chrysanthemum flowers and seeds.