Bougainvillea, like many plants, is sensitive to abrupt changes in its environment. Environmental stress is a primary cause of leaf drop. This includes sudden temperature fluctuations, especially exposure to cold drafts or frost, which can shock the plant. Bougainvillea thrives in warm climates (ideally 60–80°F or 15–27°C) and may shed leaves if temperatures drop below 50°F (10°C). Similarly, excessive heat without adequate hydration can cause dehydration, leading to leaf loss.
Improper watering is another major factor. Bougainvillea prefers a balance—neither too much nor too little water. Overwatering can lead to root rot, depriving the plant of oxygen and causing leaves to yellow and fall. Conversely, underwatering stresses the plant, prompting it to conserve water by dropping leaves. The soil should be allowed to dry slightly between waterings, ensuring good drainage to prevent waterlogged roots.
Bougainvillea requires full sun (at least 6 hours daily) to thrive. Insufficient light weakens the plant, reducing photosynthesis and causing leaves to drop as energy reserves deplete. Conversely, sudden exposure to intense, direct sunlight after prolonged shade can scorch leaves, triggering leaf drop. Gradual acclimatization to brighter light helps prevent this.
Nutrient imbalances disrupt Bougainvillea's health. A lack of essential nutrients like nitrogen, potassium, or magnesium can cause chlorosis (yellowing) and leaf drop. Conversely, overfertilization, especially with high-nitrogen formulas, promotes excessive foliage growth at the expense of flowers and may lead to salt buildup in the soil, damaging roots and causing leaf loss. A balanced, slow-release fertilizer tailored for flowering plants is ideal.
Infestations by pests such as aphids, spider mites, or scale insects weaken Bougainvillea by sucking sap from leaves, leading to discoloration and drop. Fungal diseases like leaf spot or powdery mildew can also cause defoliation. Regular inspection and treatment with insecticidal soap or neem oil for pests, or fungicides for diseases, can mitigate these issues.
When Bougainvillea is repotted or relocated, it may experience transplant shock. Root disturbance stresses the plant, often resulting in temporary leaf drop. Minimizing root damage during transplanting and ensuring consistent care afterward (proper water, light, and humidity) helps the plant recover.
Bougainvillea naturally sheds older leaves to redirect energy to new growth or flowering. Seasonal leaf drop, particularly in late winter or early spring, is normal as the plant prepares for new foliage. However, excessive or off-season leaf loss indicates underlying issues.
Bougainvillea prefers slightly acidic to neutral soil (pH 5.5–6.5). Alkaline soil can hinder nutrient uptake, leading to deficiencies and leaf drop. Poor-quality soil lacking organic matter or with inadequate drainage exacerbates stress. Amending soil with compost and ensuring proper pH levels promotes healthier foliage.
Over-pruning or improper pruning can stress Bougainvillea, causing leaf loss. While pruning encourages bushier growth, excessive removal of foliage reduces the plant's ability to photosynthesize. Prune selectively during the active growing season to avoid undue stress.
