African Violets (Saintpaulia ionantha) are among the most popular flowering houseplants worldwide, cherished for their velvety leaves and vibrant blooms. When a plant suddenly develops brown leaves, it is a frustrating signal of underlying distress. This discoloration is a common symptom that can range from a minor cosmetic issue to an indication of a severe health problem. Diagnosing the specific cause requires a careful examination of your care routine and the plant’s immediate environment.
Improper Watering Techniques and Temperature Extremes
Improper watering can cause two distinct types of browning: overwatering leads to soft, mushy tissue, while chronic underwatering causes leaf margins to dry out and turn brown and crispy. When the potting medium remains saturated, roots are deprived of oxygen, leading to root decay. This decay manifests as brown, wilting foliage that worsens despite watering.
A specific injury called ring spot, or water spot, is caused by cold water splashing onto the leaves. The rapid temperature drop destroys the cells on the leaf surface, causing necrotic spots that appear as white, yellow, or light brown rings. This cellular damage is irreversible, meaning affected leaves will not recover and should be removed.
Temperature extremes also inflict immediate damage on African Violet leaves. Exposure to cold drafts, such as those near a window or air conditioning vent, can cause the outer leaves to turn dark brown and collapse. These plants thrive in temperatures between \(60^\circ \text{F}\) and \(80^\circ \text{F}\), and sudden drops can cause shock. Conversely, placing the plant too near a hot air source can also cause drying and browning of the foliage.
Light Exposure and Chemical Build-up
The quality and intensity of light significantly influence the health of African Violet leaves. Direct, intense sunlight causes immediate damage, resulting in sunburn or leaf scorch. Symptoms of light overexposure include bleached, yellow-green areas that eventually turn dry and crispy brown. These large, irregular spots are distinct from the small, circular spots caused by cold water.
The ideal light condition is bright, indirect sunlight, which mimics the filtered light of their native habitat. Placing the plant a few feet away from a south- or west-facing window, or behind a sheer curtain, provides necessary light without the risk of scorching. Rotation of the pot is also helpful to ensure even growth.
Chemical issues, primarily from over-fertilization, can also cause browning. Fertilizer burn occurs when an excessive concentration of mineral salts accumulates in the potting mix. This salt buildup draws moisture out of the root system, leading to brown, crispy edges on the outermost leaves, known as tip burn. Visible signs include a crust of orange or yellowish crystals on the soil surface or the pot rim. To correct this, the soil should be “leached” by flushing it thoroughly with a large volume of room-temperature water to wash away the excess salts.
Identifying and Treating Pests and Diseases
When environmental factors have been ruled out, pests and diseases are the next likely cause of leaf browning.
Crown and Root Rot
One of the most serious fungal issues is Crown and Root Rot, often linked to overwatering and poor drainage. This condition causes the roots and the plant’s central crown to turn dark, soft, and mushy. The outer leaves will wilt, turn translucent brown, and collapse as the plant’s vascular system is destroyed.
Pests
Pests like cyclamen mites and thrips can also cause brown or damaged foliage. Cyclamen mites feed on the newest growth in the center of the plant, resulting in severe stunting and a discolored, brownish appearance of new leaves. Thrips, small insects, feed on plant sap, often leaving behind brown, scarred patches and distorted flowers.
Botrytis Blight
Another fungal problem is Botrytis Blight (Botrytis cinerea), which begins as small, water-soaked lesions on the leaves or petioles. These lesions rapidly expand and turn dark brown or gray. This fungus thrives in cool, damp conditions with poor air circulation.
Treatment
Treating biological issues requires isolating the affected plant immediately to prevent spread. In cases of severe Crown Rot, disposal of the plant and sterilization of the pot may be necessary, as treatment is difficult. For pests, insecticidal soap or Neem oil applied according to instructions can help manage infestations.