The chrysanthemum, often simply called a mum, is a popular choice for seasonal color displays, but the sudden decline of a newly purchased potted plant is a common experience. These vibrant flowers are often grown under ideal greenhouse conditions, and the shock of moving to a new environment can trigger a rapid downward spiral. Understanding the most common causes of distress is the first step toward diagnosing the problem and keeping your potted mum healthy.
The Root of the Problem: Hydration and Drainage
The most frequent issue leading to a potted mum’s decline involves improper watering. Mums in containers, particularly those purchased when root-bound, dry out much faster than those planted in the ground, requiring consistent moisture. Brown leaves and shriveled blooms are signs of a thirsty plant, and if caught early, a deep watering will quickly revive the foliage.
The opposite problem, overwatering, is far more destructive because it leads to root rot, a condition caused by water molds like Pythium that thrive in perpetually soggy soil. When roots are deprived of oxygen and begin to decay, they become brown and mushy, preventing the plant from absorbing water or nutrients. A plant suffering from root rot will look wilted, similar to an underwatered one, but its soil will remain damp, and the wilt will not improve after watering.
A simple way to check the plant’s moisture needs is the finger test: push your index finger two inches deep into the soil. If the soil is dry at that depth, the plant needs water, but if it is still damp or wet, withhold watering to prevent root rot. The pot must also have functional drainage holes, as sitting in standing water will quickly kill the plant.
External Stressors: Light and Temperature
Potted chrysanthemums are sun-loving plants that require a minimum of six hours of direct sunlight each day to maintain dense foliage and produce abundant blooms. Placing a mum in a location with insufficient light, such as a dimly lit porch or an indoor spot, can cause the plant to become “leggy” with sparse flowering. Indoor plants should be positioned near a south or east-facing window to receive bright, indirect light.
Rapid changes in environmental conditions can also stress the plant, leading to decline. Mums prefer a moderate temperature range, ideally between 60–70°F during the day. Placing a mum too close to a heat vent or a drafty doorway causes temperature fluctuations that weaken the plant.
Moving a mum from a protected nursery environment directly into harsh, intense afternoon sun can result in sun scald, damaging the leaves. While mums can tolerate cool temperatures and even a light frost, unexpected early hard freezes can cause the foliage to turn black and wilt, signifying severe tissue damage.
Biological Threats: Pests and Fungal Disease
If hydration and light appear adequate, the issue may be a biological threat, requiring a close inspection of the plant’s surface. Two common insect pests are aphids and spider mites, both of which are sap-sucking insects that diminish the plant’s vigor. Aphids are soft-bodied insects often clustered on new growth, leaving behind a sticky residue called honeydew.
Spider mites are difficult to spot, but their presence is indicated by fine webbing near the stems and a stippling or bronzing pattern on the leaves. To confirm an infestation, shake a branch over a white piece of paper and look for tiny moving dots. Other pests like leaf miners create whitish, winding tunnels beneath the leaf surface as their larvae burrow through the tissue.
Fungal diseases are a concern, especially when air circulation is poor or humidity is high. Powdery mildew, caused by fungi like Erysiphe, appears as a grayish-white, dusty coating on the leaves and stems. This condition depletes the plant’s energy and can cause leaves to yellow and drop. Leaf spot is another common problem, manifesting as brown or black spots on the foliage, often caused by water splashing onto the leaves during overhead watering.
Revival and Prevention: Next Steps for Potted Mums
Once the cause of the decline has been identified, immediate action can often save the plant. If the mum is severely root-bound or suffering from minor root rot, repotting it into a container a couple of inches larger with fresh, well-draining potting mix is recommended. Damaged or diseased material, including spent blooms and infected leaves, should be removed using clean shears to encourage new growth and reduce the spread of pathogens.
For minor pest infestations, a strong spray of water can dislodge many insects, while persistent issues can be treated with a targeted application of insecticidal soap or neem oil. Fungal issues like powdery mildew are managed by improving air circulation and applying a fungicide, though severely affected plants may need to be discarded to protect healthy ones.
Preventative care is the best long-term strategy for potted mums. Always water at the base of the plant to keep the foliage dry, which minimizes the risk of fungal spores taking hold. Regular deadheading, the practice of pinching off faded flowers, encourages the plant to put energy into new blooms rather than setting seed.