Sunburn

What Is Sunburn? Sunburn on plants occurs when the leaves absorb more light than they can process. When a plant is exposed to sudden, intense sunlight, the excess energy damages the cellular structure and breaks down the green chlorophyll. This results in bleached, white, or scorched patches on the leaves. Plants grown containers or in shaded greenhouses adapt to low light by producing thinner leaves that are highly efficient at capturing what little light is available. When these shade-adapted leaves are abruptly moved into direct sun, they lack the protective cuticles and pigments needed to shield themselves from intense UV rays. Signs and Symptoms Upper Canopy Bleaching: The leaves directly facing the light turn white or pale yellow. This usually happens quickly, often within a single afternoon of intense exposure. Crispy Margins: The edges of the affected leaves become dry, brittle, and brown as the tissue loses moisture rapidly. Red or Purple Flushing: Some plants develop a red or purple tint on their leaves when exposed to high light. This is a protective pigment the plant produces acting like a natural sunscreen. Sunken Patches: Tan, papery spots may appear in the middle of the leaves where the tissue has completely dried out. Wilting: The entire plant may droop severely in the hot sun as it loses water faster than the roots can absorb it. Step-by-Step: How to Treat Sunburn Move the plant immediately to a shaded, stable container location to stop further damage. Check the soil moisture. The intense heat of direct sun can dry out a pot very quickly. If the soil is dry, water the plant thoroughly. Leave partially damaged leaves on the plant. Even if a leaf has a sunburned spot, the remaining green tissue is still photosynthesizing and providing energy for the plant to recover. Prune only leaves that are more than 50% destroyed or completely dried to a crisp. Use clean, sharp shears. Do not fertilize a sunburned plant. The plant is stressed and needs to focus its energy on stabilizing, not processing new nutrients. Best Practices and Pro Tips Acclimate Slowly (Hardening Off): If you want to move an bougainvillea outside for the summer, do it over a two-week period. Start with an hour of morning sun, then gradually increase the exposure time and light intensity each day. Use Shade Cloth: If you are moving sensitive plants to a bright patio, use a shade cloth to filter the intense midday sun. Beware of Window Glass: Moving a plant from a few feet away from a window to sitting directly against the glass can cause sunburn, especially in south or west-facing windows during the summer. Bougainvillea are particularly susceptible to this issue when their environmental needs are not met. While they are resilient drought-tolerant plants in the ground, container-grown bougainvillea require careful monitoring. Cultivars like 'Barbara Karst', 'San Diego Red', and 'Texas Dawn' can quickly show symptoms if root health, lighting, or watering practices are sub-optimal. Common Mistakes to Avoid Mistake: Moving Plants Outside Abruptly. Taking a bougainvillea straight from the living room to a sunny outdoor patio is the most common cause of severe sunburn. Mistake: Cutting Off All Damaged Leaves. Pruning away every leaf with a burn spot can rob the plant of the energy it needs to recover. Only remove the worst offenders. Mistake: Fertilizing to "Heal" the Plant. Stressed plants cannot process fertilizer. Adding nutrients can burn the roots and compound the plant's problems.