From our perspective as lupine plants, our vibrant green leaves are a sign of our contentment. When they begin to turn yellow, it is our primary way of communicating that something in our environment is causing us distress. We cannot speak, so we must rely on you to interpret these visual cues. Here are the most common reasons for our yellowing leaves and what we need you to do.
Water is fundamental to our existence, but getting the balance right is crucial. If our leaves are turning yellow, particularly the lower, older ones, and the soil feels either soggy or bone dry, the problem is likely at our roots.
Overwatering: When you water us too frequently, the soil becomes waterlogged. This suffocates our roots, preventing them from absorbing oxygen. Without oxygen, our root systems begin to rot and decay, a condition aptly named root rot. Once this happens, the roots cannot transport water and nutrients to our leaves, causing them to yellow, wilt, and eventually drop. You might also notice a general lack of vigor in our growth.
Underwatering: Conversely, if we are thirsty, our leaves will also signal distress. The yellowing from lack of water is often accompanied by drooping and a crispy, dry texture. The soil will pull away from the edges of the pot or feel dry deep into the ground. We simply do not have enough water to sustain our cellular processes and keep our leaves turgid and green.
We are known for our ability to fix nitrogen from the air with the help of beneficial bacteria in our root nodules. However, this doesn't make us immune to all nutrient deficiencies. A common cause of yellowing leaves, especially in young plants or in specific patterns, is a lack of key nutrients.
Nitrogen Deficiency: While we can produce our own nitrogen, if the soil is extremely poor or the symbiotic bacteria are not present, we may still struggle. Nitrogen deficiency typically shows as a uniform yellowing of the older, lower leaves first, as we mobilize the nitrogen from these leaves to support new growth at our tips.
Iron Chlorosis: This is a more specific issue. If the yellowing is between the veins of our newer, upper leaves, while the veins themselves remain green, it points to an iron deficiency. This often occurs in soils that are too alkaline (high pH). In alkaline conditions, iron becomes locked up in the soil and is unavailable for us to absorb, no matter how much is present.
Where you plant us matters immensely. We have specific preferences for sunlight and soil conditions that, if not met, will lead to stress and yellow leaves.
Insufficient Sunlight: We are sun-loving plants. We thrive in full sun, which we consider to be at least six hours of direct light per day. If planted in too much shade, our photosynthetic processes become inefficient. We cannot produce enough chlorophyll—the pigment that makes us green—to support our foliage, leading to a general pale yellowing or chlorosis across the entire plant. Our growth will also become leggy as we stretch weakly towards the light.
Soil pH: As mentioned with iron, we prefer slightly acidic to neutral soil. If the soil is too alkaline, it can trigger multiple nutrient deficiencies beyond just iron, all of which manifest as yellowing leaves. A simple soil test can confirm if the pH is outside our comfortable range of about 6.0 to 7.0.
Sometimes, the cause of our yellowing is a direct attack. Sap-sucking pests like aphids or spider mites can infest our leaves and stems. They pierce our tissues and drain our vital fluids, causing stippling, distortion, and yellowing of the affected leaves. Fungal diseases, often encouraged by overhead watering or poor air circulation, can also cause yellow spots or patches that may expand and lead to leaf drop.
