Hardy mums (Chrysanthemum x morifolium) are perennials that provide a vibrant burst of color as the rest of the garden fades. Often called garden mums, they are distinct from the annual florist mums sold for temporary seasonal display. True hardy mums are bred for cold tolerance, surviving winter in USDA Zones 4 through 9. Cultivating these plants to return year after year is straightforward and ensures a spectacular fall show.
Establishing Hardy Mums in the Garden
The success of a hardy mum display begins with proper planting and environmental conditions. The best time to plant garden mums is in the spring after the last frost. This allows the root system a full growing season to become established before winter. Planting late in the fall gives roots little time to anchor, making them vulnerable to frost heave and winter damage.
Mums thrive in full sun, requiring a minimum of six hours of direct sunlight daily. Insufficient light causes stems to become leggy and reduces flower production. The soil should be well-drained and rich in organic matter to prevent the shallow roots from rotting.
A slightly acidic to neutral soil pH, ranging from 6.0 to 7.0, is preferred for optimal growth. When planting, amend heavy or poor-draining soil with compost or peat moss to improve structure. New plants should be spaced 18 to 24 inches apart, as they expand into bushy clumps up to two feet wide in a single season.
Before planting, the hole should be twice as wide as the root ball. Gently loosen any tightly bound roots to encourage outward growth into the surrounding soil. Set the plant at the same depth it was in its nursery pot and water thoroughly after planting to settle the soil and eliminate air pockets.
Seasonal Maintenance and Shaping Techniques
Once established, hardy mums require consistent attention to moisture and shaping throughout the spring and summer. Mums are not tolerant of dry soil, especially as they grow larger and begin to set buds. They need at least one inch of water per week, and newly planted mums may require daily watering until their roots take hold.
Apply water directly to the soil at the base of the plant rather than using overhead watering. This keeps the foliage dry, minimizing the risk of fungal diseases like powdery mildew. Fertilization supports strong vegetative growth. Apply a slow-release granular fertilizer in the spring, or use a water-soluble fertilizer monthly. A general-purpose blend, such as a 5-10-5 ratio, can be used, but all feeding must cease by mid-July.
The most specialized care technique is “pinching,” which creates a dense, compact plant with maximum blooms. If left unpruned, mums become tall, spindly, and bloom early with fewer flowers. Pinching involves removing the soft growth tip of each stem, forcing the plant to develop lateral side branches.
The first pinch should occur when new growth is about six inches tall in the spring. Subsequent pinches are performed every two to four weeks, or whenever new stems reach six inches in length, removing half an inch to two inches of growth. Stop all pinching and pruning by mid-July, or the plant will not have time to develop flower buds for a fall bloom.
Preparing Mums for Winter Dormancy
Proper end-of-season care ensures a hardy mum returns the following spring. After the first hard frost causes the foliage to die back, the plant enters dormancy. Spent stems can be cut back, but leaving a few inches of foliage intact is common practice. This dead material provides natural insulation and helps trap snow over the winter crown. The most important step for winter survival is applying a protective layer of mulch after the ground has frozen solid.
The mulch is not intended to keep the plant warm, but to maintain a consistently cold soil temperature. Apply a three to four-inch layer of loose, airy mulch, such as straw or shredded leaves, over the plant’s crown. This layer prevents the damaging cycle of freezing and thawing, which can cause the shallow root system to heave out of the soil. Remove the mulch in early spring once the threat of severe cold has passed to allow new growth to emerge.