Chrysanthemums (mums) are popular garden flowers, providing vibrant color, especially in autumn. Many gardeners are frustrated when their plants fail to thrive or return the following year. This fragility is usually a reaction to specific, correctable environmental and biological stresses, not an inherent flaw. Understanding the basic needs of the Chrysanthemum genus is the first step toward preventing plant loss.
The Silent Killer: Water and Drainage Issues
Improper watering is the most common cause of premature Chrysanthemum death. Mums need consistent moisture for heavy bloom production but cannot tolerate standing water around their roots. Soil composition and watering technique are highly important for survival.
Saturated soil deprives roots of oxygen, leading to root rot. Fungal pathogens like Pythium thrive in waterlogged conditions, causing roots to blacken, decay, and fail to take up water and nutrients. Paradoxically, a plant suffering from root rot will often wilt, appearing to need water because its damaged roots cannot function.
Use the “finger test” to check if a mum needs water: stick your finger about one inch deep into the soil. If it feels dry, water thoroughly until the excess drains freely. Container plants must have drainage holes to prevent water accumulation and root suffocation. Avoid heavy clay soils; instead, amend the soil with organic matter like compost to ensure proper aeration and drainage.
Light, Location, and Temperature Stress
Mums are sun-loving plants that need a minimum of six hours of direct sunlight daily to develop strong stems and abundant flowers. Insufficient light causes the plant to become “leggy,” stretching vertically with weak stems and producing fewer blooms.
Chrysanthemums prefer cooler temperatures, generally thriving between 56 and 70 degrees Fahrenheit. In warmer climates, intense afternoon sun can cause heat stress, leading to leaf scorching and rapid moisture loss. Partial shade during the hottest part of the day can mitigate this damage.
Proper spacing is important for maintaining plant health. Crowded conditions restrict air circulation, trapping humidity. This creates an ideal environment for fungal diseases to develop on the leaves. When planting, spacing mums 18 to 30 inches apart ensures good airflow.
Addressing Pests and Fungal Diseases
Chrysanthemums can be weakened by biological threats, even with proper care. Fungal diseases are common and often linked to high humidity or overhead watering. Powdery mildew appears as a white or grayish coating on the leaves. Rust manifests as pale yellow spots on the upper leaf surface with brown or peach-colored spore masses on the underside.
To prevent fungal issues, water the soil directly at the base of the plant and avoid wetting the foliage. If overhead watering is unavoidable, do so early in the day so leaves dry quickly in the morning sun. Removing and disposing of infected leaves immediately prevents the spread of spores.
Insect pests like aphids and spider mites cause damage by sucking sap from plant tissue. Aphids are soft-bodied insects found on new growth, leaving behind a sticky residue called honeydew. Spider mites thrive in hot, dry conditions, causing leaves to develop fine yellow stippling and sometimes thin webbing. Early detection and treatment with non-toxic options, such as horticultural soap or neem oil, manage these infestations.
Ensuring Winter Survival
A common reason mums die is a misunderstanding of their hardiness, especially those bought in the fall. Many chrysanthemums sold seasonally are “florist mums,” which are less cold-hardy and often treated as annuals. Florist mums are bred for large, showy blooms but may not survive winter because they lack the robust root system of perennial varieties.
True “garden mums” are perennial and hardy in USDA zones 5 through 9. They must be planted in the spring or early summer to allow roots sufficient time to establish before the ground freezes. Preparing these hardy varieties for dormancy involves cutting the stems back to four to six inches above the ground after the first frost.
Applying a thick layer of organic mulch, such as straw or shredded leaves, over the plant crown after the soil freezes insulates the roots from temperature fluctuations. Potted mums are susceptible to freezing because their roots lack the insulation of the surrounding ground. Overwintering potted plants in a cool, dark, and protected location, like an unheated garage or shed, ensures their return in the spring.