How to grow hardy chrysanthemums
Within the daisy family, many late-blooming perennials brighten autumn borders, yet chrysanthemums tend to be overlooked compared with their kin. The seasonal ‘mums’ that appear each fall are cultivated for a single show season rather than for enduring garden presence. In contrast, the hardy garden varieties, which have been selected for cold tolerance, form more robust root systems and thrive much better when planted outdoors. “Chrysanthemums do have an image problem,” says Judy Barker, holder of the National Collection of winter-hardy chrysanthemums. The specimens she maintains grow easily and display a wide palette that includes autumnal yellows, oranges, reds and russets together with lively pinks, bright yellows and pure, brilliant white.
How to grow hardy chrysanthemums
The optimal time for planting is during spring, specifically from April to May, after the harshest frosts have subsided. This timeframe allows the roots to establish themselves over the summer before the onset of winter. It is essential to select a location with full sun exposure and soil that is fertile and drains efficiently. While cold temperatures alone are rarely the cause of death for hardy chrysanthemums, being rooted in cold, wet clay during winter is a common issue. If your soil is heavy, consider incorporating grit or planting on a slight incline. For plants purchased in flower during October, it is key to plant them promptly while the soil is still warm.
The most critical maintenance task for these plants is pinching out. This process involves removing the top 2-3cm of the main stem, just above a leaf joint, when the young plant has reached a height of 15-20cm and has several pairs of leaves, typically in late May or early June. This can be done using just your finger and thumbnail.
As a result, the plant will produce side shoots from the leaf joints below, transforming one stem into three or four, and yielding a shorter, more robust plant with a greater number of flowers. For more vigorous varieties, you can repeat this process in late June or early July to achieve an even fuller shape. However, it is essential to cease pinching after mid-July to avoid removing the buds that would have bloomed in October.
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Taller varieties of chrysanthemums, such as ‘Emperor of China’, can grow up to 1.2m in height and are susceptible to being toppled by strong gusts of wind. To mitigate this, it is advisable to provide support early on, when the stems are around knee-high, allowing the plant to grow through the support and conceal it. A ring of hazel twigs placed around the clump can create a natural appearance in a cottage-style border, while metal link stakes or a plant cage offer a quicker and more durable solution. Waiting until the stems have already begun to lean over is a common mistake that gardeners can make, so it is essential to be proactive.
During dry spells, it is key to water deeply, soaking the soil around the roots rather than sprinkling the leaves, which can encourage the growth of mildew. Through June and July, a balanced feed applied every couple of weeks will help maintain strong growth. Once flower buds appear, switch to a high-potash feed, such as those available from Amazon, to enhance flowering and color. Cease feeding once the first flowers have opened and reduce watering as autumn approaches.
There are several types of chrysanthemums, including hardy garden varieties, which comprise the Korean and Rubellum types. These are herbaceous perennials that remain in the border throughout the year. Late-flowering or florists’ chrysanthemums, which include spiders, pompoms, and spoons, are generally tender and best suited for a greenhouse, where they can continue to bloom until Christmas. Annual chrysanthemums are grown from seed each spring, producing quick and cheerful daisies.
Caring for chrysanthemums through the seasons
Once the last flowers have faded in late autumn, you can cut hardy chrysanthemums back to a few centimetres above the ground for a tidy border. Alternatively, you can leave the old stems standing until spring. The dead stems help shelter the crown from frost and provide a habitat for insects to overwinter.
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Recommended varieties for the garden
Chrysanthemum ‘Clara Curtis’ is a single, daisy-like, mid-pink flower, the first of Amos Perry’s rubellum hybrids. It grows to 60–75cm, spreading steadily into good-sized clumps.
Chrysanthemum ‘Mary Stoker’ offers an exceptional color, with buff-yellow flowers that age to a warm apricot, and it looks exceptional with late grasses and sedums. It grows to about 70cm.
For a deeper, richer colour, ‘Ruby Mound’ bears large double ruby-red flowers from late summer into autumn. It grows to about 50 x 50cm and is a superb choice for the front of a border or a large pot by the door.
Chrysanthemum Hardy Marjolein Brown is a hardy variety and ideal for planting in containers. They look dazzling when paired with cooler tones, like whites or baby blues, for a splash of statement orange.
