Bougainvillea, a vibrant tropical vine or shrub, is famous for its stunning display of color, which actually comes from modified leaves called bracts, not the small, inconspicuous true flowers. Achieving the dramatic, cascading color requires proper nutritional support. Selecting the correct fertilizer manages the plant’s growth hormones to encourage a spectacular floral show. The type and amount of fertilizer directly influence whether the bougainvillea produces lush green foliage or masses of colorful bracts.
Understanding Bougainvillea Nutrient Needs
The nutritional profile of a fertilizer is represented by its NPK ratio, which lists the percentage of Nitrogen (N), Phosphorus (P), and Potassium (K) in that order. For bougainvillea, managing the amount of nitrogen applied is the primary concern. Nitrogen is essential for vegetative growth, promoting stems and green leaves. Excessive nitrogen, however, causes the plant to focus energy on producing lush foliage at the expense of colorful bracts.
The goal is to maintain a balance favoring reproductive growth. Phosphorus (P) is necessary for strong root development and flower initiation. Potassium (K) supports overall plant health, disease resistance, and sturdy stems. To maximize blooming, the ratio should reflect a lower proportion of nitrogen compared to phosphorus and potassium, such as a 1:2:1 or 1:3:2 ratio.
Choosing Specific Fertilizer Formulations
When selecting a fertilizer, look for formulations marketed as “bloom boosters” or those designed for flowering shrubs. These products have a higher middle number (Phosphorus) and a high third number (Potassium) relative to the first number (Nitrogen). Suitable NPK ratios include 5-10-5, 6-8-10, or a specialized 4-18-38 blend. Fertilizers with equal NPK numbers, such as 10-10-10, should be applied sparingly or diluted to prevent an oversupply of nitrogen.
Fertilizer is delivered in different forms, each offering a distinct feeding method. Water-soluble or liquid fertilizers provide nutrients immediately, suitable for a quick boost during the peak growing season. Granular, slow-release fertilizers are often preferred because they deliver a consistent, low dose of nutrients over several months. This steady feeding helps prevent the sudden growth spurts caused by high-nitrogen applications, which can interrupt the plant’s flowering cycle. Always check the product label and follow the application rate strictly to prevent root burn.
Timing and Frequency of Application
Fertilization timing should align with the bougainvillea’s natural growth cycle, involving heavy feeding during active periods and reduced feeding during rest. Begin the regular regimen in early spring as the plant emerges from dormancy and new growth starts. Continue feeding consistently throughout the summer months to support continuous blooming.
For container plants, nutrients leach out quickly, requiring more frequent feeding, such as every two to four weeks with a diluted liquid feed. In-ground plants benefit from a slower schedule, perhaps every four to six weeks, or as directed by a slow-release label. As autumn approaches, gradually reduce application frequency to allow the plant to harden off before winter dormancy. Spread the fertilizer around the plant’s drip line (the outer perimeter of the canopy) and water it in thoroughly, ensuring it does not accumulate against the main stem.
Adjusting Fertilization for Optimal Blooms
If a bougainvillea produces lush, green growth but few colorful bracts, the nutrient balance needs immediate adjustment. This issue, often called “all leaves, no flowers,” results from too much nitrogen in the system. To correct this, switch immediately to an ultra-low nitrogen, high-phosphorus fertilizer to redirect the plant’s energy toward flower production. Temporarily withholding water can also help stress the plant into blooming, which is a natural response for this drought-tolerant species.
Bougainvillea can also suffer from micronutrient deficiencies, visible in the foliage. Yellowing leaves with green veins (chlorosis) often signals a deficiency in iron or magnesium. This problem is common in alkaline soils, as a slightly acidic pH (ideally between 5.5 and 6.0) is necessary for the plant to absorb these trace elements. Applying a specialized iron chelate supplement or a magnesium source like Epsom salts can correct these deficiencies.