Winter Care of Hardy Chrysanthemums

Hardy chrysanthemums have become very popular for planting into the landscape in full bloom in early fall to provide quick landscape color. The proliferation of varieties with different flower forms and colors have helped increase their desirability. There are a few other perennial garden flowers that bloom in fall, but none are as spectacular as well-grown chrysanthemums.

By December the blooms are gone and the spectacle is over. What should be done with these plants now? The common name, ‘hardy chrysanthemum’, might indicate they are able to endure our climate like a peony or iris. Unfortunately, there is considerable variability in the hardiness of the numerous varieties. Hardiness may also vary with location, culture, site or winter severity, so there is no dependable way of categorizing varieties as to hardiness.

If a plant is to survive for another season, it is better to assume that the new variety, whether planted in spring or in fall, will need some winter protection. If plants are still in pots, be aware that the roots are not as cold-hardy as the tops, and they will be unlikely to survive the winter that way outdoors. Gardeners who have cold frames or cool greenhouses could move them into such protective structures for survival while still in the pots.

Gardeners without any type of protective structure might try placing the potted mums in a bright window in a cool room (about 40 – 45 degrees) for the winter. Shoots should develop from the base. The tops may be cut off after new basal shoots are seen. Soil in the pots should be kept lightly moist, but not excessively wet for overwintering this way. The other alternative is to plant them outdoors into the garden and protect them as much as possible. If the mum plants were grown in a field and dug from a field soil, or in a pot with a mix that contained soil, their survival rate will be better than for those grown in pots containing a totally organic mix of peat moss or compost. If the medium in the pot is very different from the existing garden soil, amend it with liberal amounts of organic matter to reduce this difference.

Greater compatibility will allow better root establishment and spread. Mums normally have a fairly shallow root system. If the soil is a fairly heavy clay and pots are deep, the roots at the bottom of the pot may suffocate after they are positioned deeply in the soil. By making a slit in the ball from the base upward about half way and then fanning out the bottom, roots can be placed more shallowly. Slicing the root ball will kill some roots, but those roots that survive will be positioned better for establishment. In very loose, open soils, this is not necessary. This approach is not necessary for field-grown plants.

Healthy plants should be producing some basal shoots by this time. If they are not, their chances of winter survival are less than for those plants that have produced them. You may also note a difference in the position of shoot development between varieties. Some varieties will produce shoots from stems creeping below the soil while others may produce shoots only on the base of the woody stems. Shoots existing only from stems above ground are more exposed and more subject to winter damage than those coming from below ground. Pull soil up around the stems and shoots of such plants to increase survival.

For any mums in the garden a mulch can help them survive the first winter as well as succeeding winters. Cut back the tops after leaves have turned brown. Use several inches of a loose, airy mulch that will allow light to get to the small shoots throughout the winter. Loose straw or evergreen branches anchored in place so wind will not blow them away can provide enough protection. These materials are not intended to keep plants warm, but only to provide wind protection and keep the soil shaded and frozen to avoid the shoots heaving upward during periods of freezing and thawing. These protective mulches may be removed or pulled away from the crown of each plant by early to mid April after any danger of severe cold is past.

How to Grow Annual Chrysanthemum

Grow annual chrysanthemums in full, hot sun, cutting off dead blooms and keeping them well-watered during the blooming period. Cut chrysanthemums down to the ground once they start to get slimy with advice from a sustainable gardener in this video gardening.

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