From my roots' perspective, the soil is my only kitchen. When my leaves turn yellow, especially if it's the older leaves first, it's often because I'm missing key ingredients. Nitrogen is crucial for my green chlorophyll, and without it, I can't photosynthesize properly, so I start to cannibalize the older leaves to support new growth. A lack of iron (showing as yellow leaves with green veins on new growth) or magnesium (yellowing between the veins of older leaves) has a similar effect. It's not always that the nutrients aren't in the soil; sometimes the pH is wrong. I prefer my soil slightly acidic (pH 6.0-6.5). If it's too alkaline, I literally cannot absorb the iron that is present, no matter how much you feed me.
You might think you're helping me by giving me plenty of water, but too much is a death sentence for my root system. My roots need oxygen as much as they need water. When I'm sitting in soggy, poorly drained soil, my roots begin to suffocate and rot. Once this happens, they cannot function. They cannot take up the water and nutrients my leaves and canes desperately need. This causes a generalized yellowing of my leaves, often followed by wilting—a confusing sign because I look thirsty when the problem is actually that I'm drowning. Compacted soil can create the same oxygen-starved environment without overwatering.
The opposite problem is just as damaging. When I don't receive enough water, my systems go into survival mode. To conserve water, I will begin to drop leaves. Before they drop, they will turn yellow and then brown and crispy, starting at the edges and tips. This is especially common during the peak heat of summer. The intense sun and heat can simply be too much, scorching my leaves and causing them to yellow and burn, even if my water needs are marginally met. It's a stressful combination of losing water through my leaves faster than my roots can replace it.
Look closely at my yellowing leaves, especially on the undersides. If you see tiny webs, specks, or insects, I am under attack. Spider mites are a common culprit—they pierce my leaf cells and suck out the chlorophyll and nutrients, leaving behind a stippled, yellow appearance. Other sap-sucking pests like aphids or leafhoppers can cause similar yellowing and weaken me significantly. Their feeding damages the leaf cells and can also introduce diseases.
Fungal pathogens are a silent battle I often fight. Black spot is the most famous one for roses like me. It starts as its name suggests, with black spots on the leaves, but it quickly leads to yellowing around the spots. Eventually, the entire leaf turns yellow and falls off. This fungus disrupts my ability to function and drains my energy. Another disease, rose mosaic virus, causes irregular yellow patterns or lines on my leaves, sapping my vigor over time. These diseases spread easily, especially in humid conditions with water on my foliage.
