The Bougainvillea is a hardy plant that thrives in hot, sunny climates. Despite its tough nature, the plant often signals distress through a change in its foliage color. The yellowing of Bougainvillea leaves, known as chlorosis, indicates an imbalance in its care or environment. This discoloration happens when the plant cannot produce enough chlorophyll, the pigment responsible for the green color and photosynthesis. Identifying the precise cause of this yellowing is the first step toward restoring the plant’s healthy appearance.
Common Environmental Causes of Yellowing
Watering practices are the most frequent reason for Bougainvillea leaves to turn yellow. Overwatering, often coupled with poorly draining soil, suffocates the roots and leads to root rot. When roots are compromised, they cannot effectively absorb oxygen and nutrients, resulting in pale, yellowing leaves that may eventually drop off. Conversely, underwatering causes severe drought stress, especially in hot weather, leading to a defensive response where the plant sacrifices older leaves to conserve moisture.
Bougainvillea requires intense light to maintain deep green foliage and produce blooms. The plant needs a minimum of six hours of direct, unfiltered sunlight each day to thrive. If the plant is situated in a location with insufficient light, its metabolic processes slow down, and the leaves may become weak and pale as the plant struggles to photosynthesize effectively. Moving the plant to a brighter location often resolves this light-induced chlorosis quickly.
Sudden shifts in temperature can also induce shock, causing leaves to yellow and drop rapidly. Bougainvillea is intolerant of cold, and exposure to temperatures consistently below 45 to 50 degrees Fahrenheit (7 to 10 degrees Celsius) can trigger this stress response. This is often observed during a sudden autumn cold snap or when a potted plant is moved from a warm indoor environment to a cooler outdoor space.
Nutrient Imbalances and Soil pH
If environmental factors like watering and light are ideal, the yellowing may point to specific nutritional deficiencies. A lack of nitrogen is a common issue, typically presenting as a uniform, pale yellowing across the entire leaf. Because nitrogen is a mobile nutrient, the plant prioritizes new growth, causing the older, more mature leaves to yellow first as the nitrogen is drawn away to support younger tissue.
More complex deficiencies involve micronutrients, which often display a distinct pattern called interveinal chlorosis. If the leaf veins remain green while the tissue between them turns yellow, the plant is likely suffering from an iron deficiency. This symptom is most visible on the newest growth because iron is an immobile nutrient and cannot be relocated from older leaves.
A magnesium deficiency also causes interveinal yellowing, but it usually begins on the older leaves and may include reddish or brown tints along the leaf margins. The availability of these micronutrients is governed by the soil’s pH level. Bougainvillea prefers a slightly acidic soil environment, ideally with a pH between 5.5 and 6.5.
When the soil becomes too alkaline (high pH), micronutrients like iron become insoluble and unavailable for the roots to absorb. This phenomenon, known as nutrient lockout, means the necessary nutrients may be present in the soil but are chemically inaccessible to the plant. Addressing the soil chemistry is therefore necessary to correct these micronutrient deficiencies.
Step-by-Step Recovery Plan
The first step in recovery is to correct any watering mismanagement by establishing a deep, infrequent routine. Allow the top two inches of soil to dry out completely before saturating the soil thoroughly until water drains from the bottom of the pot or planting area. This practice promotes a deeper, more resilient root system better equipped to handle periods of drought.
If the yellowing is diagnosed as a nutrient deficiency, a targeted fertilization strategy should be implemented. For general yellowing, apply a balanced fertilizer that is formulated with a high level of potassium to support overall plant health and encourage flowering. If interveinal chlorosis is present, use a chelated iron supplement, which provides the iron in a form that is immediately available for root uptake even in high-pH soil.
To address a high soil pH that is causing nutrient lockout, incorporate acidifying agents into the soil. Applications of elemental sulfur or ammonium sulfate can gradually lower the pH, restoring the availability of essential micronutrients. Always test the soil pH before applying these amendments to ensure the adjustments are precise.
Finally, inspect the plant closely for signs of common pests like spider mites or aphids, as their feeding can also cause stippling and discoloration. Prune any severely yellowed or damaged foliage to redirect the plant’s energy toward new, healthy growth. For plants suffering from light deficiency, relocate them to a spot that receives at least six hours of direct sun immediately.