Fertilizing bonsai: when, how and which product to use ?

Bonsai Fertilization: The Key to a Healthy Tree

Fertilization is a fundamental element in ensuring the vigor, balance, and beauty of a bonsai. A well-draining substrate low in natural nutrients, regular pruning cycles, and often cramped pots make nutrient inputs essential. But is it absolutely necessary to choose a "special bonsai" fertilizer ? Not necessarily.

At the nursery, we chose a universal mineral fertilizer NPK 12-12-17 (+2MgO), originally intended for tomatoes. Simple, complete, and effective, it has proven to be perfectly suited to our trees, regardless of their species.

Which fertilizer should you choose for a bonsai? Comparison of the main categories

1. Organic fertilizers (solid)

Examples: manure pellets, compost, vegetable oil cakes, Biogold

• ✅ Advantages : slow-release, enriches soil microbial life, very low risk of burns
• ❌ Disadvantages : sometimes strong odor, slow effect, reduced effectiveness in cold weather

2. Mineral fertilizers (solid or granular)

Examples: NPK 12-12-17 granules

• ✅ Advantages : fast and measurable action, precise composition, long shelf life, easy to dose
• ❌ Disadvantages : no biological effect on the soil, requires careful dosing

3. Liquid fertilizers

Examples: bonsai fertilizer to be diluted in water, growth promoters

• ✅ Advantages : immediate action, useful in case of temporary deficiency
• ❌ Disadvantages : effect too short, dissolves too quickly, risk root burns, requires frequent feeding

❌ Why we don't recommend liquid fertilizers

Liquid fertilizer is often tempting for its ease of use, but we strongly advise against it for regular use on trees.

• It dissolves immediately in the irrigation water, making its action very short-lived.
• There is a real risk of root burn, especially if the tree is underwatered or during periods of extreme heat.
• It is difficult to dose precisely and can quickly lead to imbalance or deficiencies if used incorrectly.

In summary : it is suitable for occasional applications, but not as a primary fertilization.

✅ Why we use a universal mineral fertilizer in granules

The NPK 12-12-17 (+2MgO) fertilizer we use is not originally specific to bonsai—it is a universal fertilizer, designed for vegetable crops (especially tomatoes). But it's precisely its simplicity, consistency, and balanced composition that make it an excellent choice for growing in pots. 

Composition :

• 12% Nitrogen (N) : for stem and leaf growth
• 12% Phosphorus (P) : for root development
• 17% Potassium (K) : for flowering, general health, and resistance
• 2% Magnesium (MgO) : to promote nutrient uptake and intensify foliage color
• 22% Sulfuric Anhydride (SO₃) : soluble and assimilable
• Trace elements : Boron, Copper, Iron, Manganese, Zinc, etc., essential for plant health

How to use

Apply every 2 months, from approximately May to October

Recommended dosage :

Spread over the surface of the substrate, then water lightly.

 ⚠️ Caution : Overdosing can weaken or even kill the tree.

Can you alternate with an organic fertilizer?

Yes! We even recommend alternating with an organic fertilizer, such as well-rotted horse manure, to sustainably enrich the soil and stimulate microbial life. This is a good way to balance rapid application with a more natural nutrient base. In this case, you can alternate monthly between mineral and organic fertilizer.

In summary

There are a wide variety of bonsai fertilizers, and each can be suitable for a given context or method. For our part, we have chosen to keep it simple, effective, and stable: a solid, universal mineral fertilizer that is easy to manage and perfectly suited to the growing conditions of our nursery.

This is not an absolute rule : other formulas may work, but this one suits us very well because it is a reliable and accessible solution.