From my perspective as a hollyhock, my yellowing leaves are my primary way of communicating that I am under stress. It is a symptom, not a disease itself, and it can have several underlying causes. Here is a detailed diagnosis from my point of view.
My root system is crucial, and its environment directly affects my foliage. If the soil is constantly waterlogged, my roots cannot breathe. They begin to suffocate and rot, a condition aptly named root rot. With a damaged root system, I cannot uptake water or nutrients effectively, and my lower, older leaves will turn yellow and wilt as a first sign. Conversely, if I am not receiving enough water, I will go into survival mode. To conserve resources, I will sacrifice my older leaves, causing them to turn yellow, become crispy, and eventually drop off. My ideal condition is consistently moist, well-draining soil.
To maintain my vibrant green leaves and support my tall flower spikes, I require a balanced diet. A lack of key nutrients will manifest as chlorosis, the technical term for yellowing. If the yellowing appears on the older leaves first, it often indicates a deficiency in mobile nutrients like Nitrogen (N), which I can move from old growth to support new growth. If the yellowing is between the veins of newer leaves, it may point to an immobile nutrient deficiency like Iron (Iron chlorosis) or Manganese, often exacerbated by soil that is too alkaline.
I am notoriously susceptible to fungal diseases, and yellowing leaves are a classic early warning. Rust (*Puccinia malvacearum*) is my most infamous adversary. It begins as yellow spots or flecks on the tops of my leaves, with corresponding orange-brown pustules on the undersides. As the infection progresses, the entire leaf can yellow, wither, and die. Other fungal issues like Anthracnose or Hollyhock Blight also cause yellowing or browning spots that expand, compromising my ability to photosynthesize.
Certain pests can directly cause my leaves to yellow by draining my sap, which is my lifeblood. Spider mites are tiny arachnids that create fine webbing and cause a stippled, yellow appearance on leaves as they feed. Other sap-suckers like aphids can also cause leaf distortion and yellowing. Their feeding weakens me and can introduce other diseases.
Finally, my location and your gardening practices play a role. If I am planted in extremely dense, poor soil, my roots cannot establish properly. If I am overcrowded and lack air circulation, the humid environment promotes fungal growth. Even natural aging can be a factor; it is normal for my very oldest, bottom leaves to yellow and drop as I divert energy to flowering and new growth at my apex.
