Fertilizing is essential for healthy bonsai, even more so than for most plants. Because bonsai are grown in small containers, their roots have limited access to nutrients. Traditional bonsai soils are designed for excellent drainage and contain little organic matter, meaning they don’t naturally hold or release many nutrients.

Why Fertilization Matters

Two main factors make feeding critical for bonsai:

1. Limited root space – Less soil means fewer available nutrients.
2. Low-nutrient soil mixes – Designed for drainage, not nutrient retention.

For this reason, bonsai should be on a consistent feeding schedule during their growing season. Feed when new growth appears in early spring, and continue through summer into fall. In autumn, shift to a fertilizer formula better suited for hardening growth before winter. Temperate species that drop their leaves should not be fed in winter, while tropical/indoor varieties should receive reduced feedings during this time.

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Understanding Nutrients

Macronutrients – Every bonsai fertilizer should contain nitrogen (N), phosphorus (P), and potassium (K). Fertilizer labels always list them in that order, e.g., 15-10-6.

• Nitrogen (N) – Encourages leaf and stem growth, and deep green color. Young bonsai need higher nitrogen; mature trees do best with moderate levels.
• Phosphorus (P) – Supports flowers, fruits, root health, and energy storage. Use higher phosphorus in late summer to early fall to prepare trees for winter.
• Potassium (K) – Improves disease resistance, trunk strength, and overall vigor.

Micronutrients – Essential in small amounts, including calcium, copper, iron, manganese, molybdenum, and zinc. Many commercial fertilizers include these, but they can also be added separately each year.

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Fertilizer Types

Organic Fertilizers – Improve soil structure and release nutrients slowly, reducing the risk of overfeeding.

Inorganic Fertilizers – Available in liquid, pellet, slow-release, and soluble forms. They act quickly and are easy to measure. Many bonsai growers alternate between organic and inorganic feeding for balanced results.

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Our Recommended Fertilization Program at the Bonsai Learning Center

We follow a two-step program to keep our trees healthy, vigorous, and balanced throughout the year.

Step 1 – Organic Cakes with Fertilizer Cups

Place organic fertilizer cakes on the soil surface, secured with fertilizer cups. When you water (or it rains), nutrients seep into the soil while the cups prevent solids from clogging the inorganic mix. Replace the cakes every 4–5 weeks, as nitrogen depletes in that time.

Step 2 – Liquid Feeding Cycle

Apply Bonsai Pro 7-9-5 every two weeks. Alternate feedings with fish emulsion/kelp every other time:

• Week 1: Bonsai Pro
• Week 3: Bonsai Pro/Fish emulsion/kelp
• Week 5: Bonsai Pro again

Once a month, mix in Micrototal foliar fertilizer with the Bonsai Pro for added micronutrients.

Perform both steps from spring to fall.  Here in North Carolina that is March through September, which covers the main growing season.

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Seasonal Adjustments

From October to December, we switch to a nitrogen-free formula like 0:10:10 fertilizer. This promotes root health during winter dormancy without encouraging new top growth that could be damaged by frost.

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Key takeaway: Whether using organic cakes, liquid fertilizers, or seasonal adjustments, the most important factor is consistency. By providing a balanced mix of macro and micronutrients in a regular schedule, your bonsai will remain strong, healthy, and ready to thrive year after year.