Why Are My Chrysanthemum Leaves Turning Yellow?

Yellowing leaves on chrysanthemums are a signal that something isn’t right. Sometimes it’s a natural part of ageing, but it can also point to water stress, nutrient deficiencies, pests, or disease. The good news is that most causes are easy to identify and correct with a few changes in care. Below is a complete guide to diagnosing and fixing yellow leaves on mums.

Natural Ageing vs. Stress

Older leaves at the base of the plant naturally yellow and drop off as chrysanthemums focus energy on new shoots and flowers. If the yellowing is limited to the lowest leaves and the rest of the plant looks healthy, this is likely normal. However, widespread yellowing across the plant usually signals stress.

Watering Problems

Both underwatering and overwatering can cause yellow leaves. If soil is dry and crumbly, the plant is stressed from lack of water. If soil is soggy and roots are suffocating, yellowing will also appear, often with limp leaves. Water deeply 2–3 times per week, always at the base, and use mulch to regulate soil moisture. Well-drained soil is critical — soggy conditions quickly turn leaves yellow and promote root rot.

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Nutrient Deficiencies

Yellow leaves often point to a nutrient imbalance. Nitrogen deficiency shows as uniform yellowing across older leaves, while magnesium or iron deficiency causes yellowing between the veins, leaving veins green. To prevent this, feed chrysanthemums regularly during the growing season.

Growth stage (spring–summer): Apply NPK 20-20-20 Plant Fertiliser every 3–4 weeks. This balanced feed supports strong foliage and root growth, preventing nitrogen deficiency.
Budding & flowering (late summer–autumn): Switch to NPK 4-18-38 + Calcium & Magnesium. This provides potassium for flower development plus calcium and magnesium to prevent leaf yellowing caused by deficiencies.

Pests and Disease

Sap-sucking insects like aphids, spider mites, and thrips drain nutrients from leaves, leaving them yellow, stippled, or curled. Inspect the undersides of leaves and treat infestations early. Fungal issues such as root rot and leaf spot can also cause yellowing, especially in damp conditions. Improve airflow, water at the base, and remove affected foliage promptly.

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Prevention and Long-Term Care

To keep chrysanthemum leaves healthy and green, combine consistent watering, regular feeding, and good airflow. Avoid overcrowding plants, stake taller varieties, and deadhead spent blooms to reduce stress. Regularly dividing clumps every 2–3 years also rejuvenates root systems and improves nutrient uptake.

FAQs – Yellow Chrysanthemum Leaves

Is yellowing always bad? Not always — older leaves naturally yellow and fall, but widespread yellowing suggests a problem.
Can overwatering cause yellow leaves? Yes, soggy roots starve the plant of oxygen, leading to limp yellow foliage.
What deficiency causes yellow leaves? Low nitrogen, magnesium, or iron are common culprits.
How can I fix nutrient yellowing? Feed with NPK 20-20-20 during growth, and NPK 4-18-38 + CaMg during flowering.
Do pests make leaves yellow? Yes, aphids, mites, and thrips damage leaf tissue and drain nutrients, causing discolouration.