Hello there, dedicated plant caregiver. I am your Crassula, a resilient succulent built for sun and sparse water. When you see brown spots marring my plump, green leaves, it's my way of communicating that something in my environment is out of balance. It's not always a death sentence, but it is a signal you should heed. Let me explain the two most common culprits from my perspective.
As a sun-loving plant, I thrive on bright light. However, just like human skin, my leaves can get sunburned. This is not a disease caused by a pathogen, but a physical injury from excessive ultraviolet radiation. It typically happens when my living conditions change abruptly. If I've been living on a shaded shelf indoors and you move me directly to a blazing, south-facing windowsill or outside into the full summer sun without a gradual transition, my photosynthetic tissues can't cope. The intense light literally cooks the cells, causing them to die and turn a crispy, light brown or tan color.
You can identify sunburn by its distinct pattern. The spots are often concentrated on the top leaves that receive the most direct light, particularly on the side facing the sun. The affected areas are dry, papery, and sunken. They will not spread to other parts of the leaf or to other plants because it is not contagious. It is simply a scar from an event that has already passed.
When brown spots are caused by disease, the situation is more serious. This is an active, often spreading problem, usually triggered by excess moisture. The most common cause is water sitting on my leaves for too long, especially if I'm in a spot with poor air circulation. Fungi and bacteria thrive in these damp, stagnant conditions.
Unlike the dry, crispy spots of sunburn, disease-related spots often look different. They may start as soft, dark, water-soaked lesions. They can feel mushy to the touch, a sign of rot. A key indicator is that these spots can enlarge and spread to other leaves and parts of my stem. If you see a brown spot that started small and is gradually growing, or if a leaf turns yellow around the brown spot, it is likely a fungal or bacterial issue. In advanced stages, you might even see a fuzzy mold (fungal) or a slimy ooze (bacterial). This type of problem will not resolve on its own and requires your intervention.
To diagnose the issue, please look closely at the spots and consider my recent history. Ask yourself: Was there a recent, sudden increase in light exposure? If yes, it's likely sunburn. Have you been watering from above, getting my leaves wet, or has the weather been humid and cool? If yes, disease is the prime suspect.
For sunburn, the damage is permanent, but the leaves will often continue to function if the burn isn't too severe. Move me to a location with bright but indirect light for a few weeks to acclimate. You can then gradually reintroduce me to more direct sun. There is no need to remove the sunburned leaves unless they are entirely dead; I can still photosynthesize with the healthy green parts.
For disease, you must act quickly. Isolate me from your other plants to prevent the pathogen from spreading. Using sterile shears, carefully cut away all affected leaves and stems, making sure to remove a small portion of the healthy tissue as well to ensure you've excised all the infection. Hold off on watering until my soil is completely dry. In severe cases, you may need to apply a fungicide. Most importantly, change your watering habits: always water at the base of my stem, directly onto the soil, and only when the soil is completely dry.
