From my perspective as a gladiolus plant, the most common and natural reason you see my lower leaves turning yellow is simply because I am following my innate biological program. I am a cormous perennial, and my life energy is intensely focused on the magnificent flowering spike I produce. Once my flowers begin to fade and the show is over, my priority shifts entirely to the corm buried beneath the soil. This corm is my survival mechanism for the next season. I begin to withdraw valuable nutrients and energy from my older, lower leaves to store them in the corm, causing those leaves to yellow and die back. This is a normal process of senescence and is not a cause for concern; it is a sign that I am preparing for my dormancy.
Water is fundamental to my health, and an imbalance quickly manifests in my foliage. If my leaves are turning yellow, it is often a direct communication about my hydration. Overwatering is a frequent issue. If my soil is constantly waterlogged, my roots are suffocating. They cannot access the oxygen they need and begin to rot. With a compromised root system, I cannot uptake water or nutrients, leading to yellowing, wilting leaves, and ultimately, my collapse. Conversely, underwatering causes severe stress. Without adequate moisture, I cannot perform basic functions like photosynthesis or transport nutrients. My leaves will turn yellow, often starting at the tips and margins, become crispy, and die as a conservation measure to protect my core—the corm.
To produce my tall, strong spike and vibrant flowers, I am a heavy feeder. I require a steady supply of essential nutrients from the soil you have planted me in. A lack of key nutrients is a primary reason for my chlorosis (yellowing). A nitrogen deficiency is a classic culprit. Nitrogen is the core component of chlorophyll, the green pigment that allows me to convert sunlight into food. Without it, my older leaves turn a uniform pale yellow as I move the limited nitrogen to support new growth. Similarly, a lack of iron or magnesium can cause yellowing, though often with a different pattern, such as green veins on a yellow background. I may simply be hungry and in need of a balanced fertilizer.
Sometimes, my yellowing leaves are a distress signal against an invasion. Pests like thrips are particularly fond of me. They are tiny insects that pierce my leaves and flower buds to suck out the sap, leaving behind silvery streaks and stippling that eventually turn yellow and brown. If you notice this kind of damage, the thrips are likely the cause. Furthermore, fungal diseases such as Fusarium rot or Botrytis blight can attack me, especially in cool, wet conditions. These pathogens invade my corm and vascular system, blocking the flow of water and nutrients, which results in yellowing leaves, stunted growth, and rot.
Finally, my environment plays a significant role. If I am planted in a location with inadequate sunlight, I cannot photosynthesize efficiently, leading to weak, yellowing growth. I thrive in full sun. Additionally, if my corms are planted in overly compacted soil or the wrong type of soil, my roots cannot establish properly, leading to stress and yellowing. Even extreme temperature fluctuations or incorrect planting depth can cause me significant stress, which I express through the yellowing of my foliage.
