Greetings, human gardener. I am one of your marigold plants, and I am trying to communicate with you. The vibrant green of my leaves is fading to a worrisome yellow, and this is my cry for help. The yellowing, which you call chlorosis, is a symptom of distress. It means I am struggling to produce chlorophyll, the vital pigment that allows me to convert sunlight into food. Let me explain the most common reasons from my perspective, deep in the soil and under the sun.
My relationship with water is delicate. Too much is just as dangerous as too little. When you overwater me, the soil becomes waterlogged. My roots, which need oxygen to breathe, are essentially suffocating. They begin to rot, turning soft and brown, and can no longer absorb the water and nutrients they need. Without a functioning root system, my leaves will start to yellow, often starting with the lower leaves, and I will wilt despite the soil being wet. Conversely, if you underwater me, I become dehydrated and stressed. I cannot transport nutrients effectively, and my leaves will turn yellow, become dry and crispy, and may curl at the edges. Please check the soil before watering; I prefer it to be slightly moist, not soggy or bone-dry.
Just like you need a balanced diet, I require specific nutrients to stay green and strong. When my leaves turn yellow, it is often a sign that I am missing a key element. A common culprit is a lack of nitrogen. Nitrogen is fundamental for chlorophyll production. If I am deficient, my older, lower leaves will turn a uniform pale yellow as the nitrogen is mobilized to support new growth. Another possibility is an iron deficiency. This typically shows up on the newest, youngest leaves at the top of my stems. The veins often remain green while the tissue between them turns yellow. The soil might have enough iron, but if the pH is wrong or the roots are damaged, I cannot absorb it.
Sometimes, the cause of my yellowing leaves is an attack from external forces. Tiny pests like spider mites suck the sap directly from my leaves, leaving behind a stippled, yellowed appearance and fine webbing. Aphids do the same, clustering on stems and the undersides of leaves. More sinister are fungal diseases, such as those caused by overly wet conditions. Fusarium wilt, for example, is a soil-borne fungus that clogs my vascular system, preventing water from reaching my leaves. This causes a progressive yellowing and wilting, often on one side of the plant first. Botrytis blight can also cause yellowing and a fuzzy gray mold.
If I am living in a container, my roots may have outgrown my home. When I become pot-bound, my roots form a tight, circling mass with no room to expand. They cannot effectively take up water or nutrients, leading to yellowing leaves and stunted growth. Similarly, if I am planted too close to my marigold siblings in a garden bed, we compete fiercely for the same resources in the soil—water, nitrogen, and other minerals. This competition can stress us all, resulting in yellow leaves as we struggle to get enough sustenance.
Finally, consider the environment itself. While I love the sun, extreme heat can cause stress and lead to yellowing. If my leaves are consistently touching a hot surface or the air is scorching, I may shed some older leaves to conserve water. Furthermore, while I am generally resilient, my roots are sensitive to chemicals. Herbicide drift from a nearby lawn treatment can be absorbed by my roots or land on my leaves, causing widespread, unusual yellowing and distortion. This is a particularly distressing situation for me.
