The presence of brown leaves on a geranium signals significant stress, leading to the death of leaf tissue, known as necrosis. Browning is a symptom indicating various potential issues, from improper care to disease. Fixing the problem requires a methodical approach, starting with a careful inspection to identify the specific pattern of damage, which points toward the underlying cause.
Diagnosing the Pattern of Leaf Browning
Understanding the visual characteristics of the damage is the first step, as different stresses and pathogens create distinct patterns on the foliage.
Brown, crispy edges and tips often suggest dried-out leaf tissue from a lack of moisture. This pattern frequently results from underwatering, excessive heat, or low humidity.
Yellowing leaves with brown, mushy spots or browning at the base of the plant indicates soft, dark necrosis. This is typically associated with fungal or bacterial issues that thrive in overly wet conditions, leading to cell breakdown. Conversely, brown spots with defined, circular borders often point directly to specific leaf-spot diseases, which create distinct lesions.
An overall leaf browning or scorching across the entire surface, appearing suddenly and uniformly, is often an immediate reaction to environmental shock. Examples include intense, direct sunlight or a damaging application of fertilizer. Matching the visual category to the symptoms narrows the field of possible causes.
Remedying Watering and Root Issues
Water management issues are the most frequent cause of brown leaves, as geraniums are sensitive to both extremes of moisture. Overwatering is detrimental because it starves the roots of oxygen, leading to root rot. Healthy white roots become dark, soft, and mushy. When roots fail, the plant displays dehydration symptoms, such as wilting and browning lower leaves, even if the soil is saturated.
To correct this, allow the soil to dry out appropriately between watering cycles. A simple finger test—checking the soil moisture one to two inches below the surface—is a reliable method for determining when to water again. The pot must have adequate drainage holes, and saucers should be emptied shortly after watering to prevent the plant from sitting in stagnant water.
For chronic overwatering problems, the underlying issue might be poor soil structure, such as heavy or compacted potting mix that retains too much moisture. In these cases, repotting into a loose, well-draining mix amended with perlite or coarse sand provides a structural fix. Geraniums tolerate drier conditions better than waterlogged soil, so allow the top layer of soil to dry completely before rehydrating.
Adjusting Light, Temperature, and Feeding
Brown leaves can also result from abiotic stressors, including light, temperature, and nutrient imbalances.
Light stress manifests as leaf scorch, where intense, direct afternoon sunlight causes brown, bleached patches. Moving the plant to a location with bright, indirect light or morning sun prevents this localized tissue damage.
Temperature stress causes browning when a geranium is subjected to sudden changes, such as a cold snap or prolonged exposure to high heat. Geraniums thrive best when daytime temperatures are consistently warm. Sudden exposure to near-freezing conditions causes cellular damage and subsequent necrosis. Protecting plants from abrupt environmental shifts is the primary mitigation strategy.
Nutritional stress frequently presents as fertilizer burn, characterized by crispy, brown tips and margins. This occurs because excess fertilizer salts draw moisture out of the plant cells, desiccating the foliage. To treat fertilizer burn, the soil must be “leached” by slowly flushing the pot with large volumes of plain water to wash away accumulated salts. Resume feeding with a diluted, balanced fertilizer following recommended seasonal timing.
Identifying and Treating Biotic Threats
When environmental factors are ruled out, brown leaves may be caused by biological agents, such as pests or diseases.
Fungal diseases like Botrytis blight (gray mold) cause brown, water-soaked spots that quickly develop a fuzzy, gray-brown texture in humid conditions. Geranium rust creates pale spots on the upper leaf surface and rust-colored spore pustules on the underside.
Bacterial leaf spot, caused by pathogens like Xanthomonas campestris, often results in small, dark brown lesions surrounded by a yellowish halo. These diseases spread by water splashing onto the leaves, emphasizing the importance of watering the soil directly and ensuring good air circulation. Immediate treatment involves carefully pruning and disposing of all infected leaves and stems to prevent the spread of spores or bacteria.
If pests like spider mites or whiteflies are the issue, browning may be accompanied by fine webbing or visible insects on the undersides of the leaves. Pests require targeted intervention. Treatments include washing the foliage with insecticidal soap or a gentle stream of water, and isolating the affected plant to prevent the infestation from spreading.