Best Fertilizer for Longan Tree: Feeding Guide for Abundant Fruiting

The longan tree (Dimocarpus longan), also known as dragon eye fruit, is a subtropical evergreen prized for its sweet, translucent fruit. Closely related to lychees, longan trees thrive in warm, frost-free areas of Australia and require a strategic fertiliser program to promote consistent flowering and heavy fruiting year after year. Whether you’re growing Kohala, Biew Kiew, or another popular longan cultivar, proper nutrition is essential during each phase of growth—especially in sandy or nutrient-depleted soils common across Queensland and northern NSW.

Longan Tree Growth Stages and Nutrient Demands

Longans have a distinctive growth cycle made up of vegetative growth (leaf and branch formation), flowering, fruit set, and dormancy. These stages are strongly influenced by seasonal rainfall and dry spells—particularly in Australia’s subtropical zones. Unlike temperate fruit trees, longans don’t respond well to fertiliser at random points in the year. Instead, fertilisation must be timed to match growth phases. Key nutrient needs:

Nitrogen (N): Needed in moderation to support leafy growth and early canopy development
Phosphorus (P): Encourages flowering and strong root development, especially important for young or recently transplanted trees
Potassium (K): Vital for fruit set, sugar accumulation, and preventing fruit drop
Calcium & Magnesium: Support cell strength, nutrient transport, and improve fruit quality

Overfeeding with nitrogen is a common mistake in backyard longan care. It results in lots of green growth but few or no flowers. Instead, high-potassium, low-nitrogen fertilisers like CompleteGrow NPK 4-18-38 + CaMg are preferred, especially for mature, fruit-bearing trees. This ratio supports flower spike development while enhancing fruit firmness, sweetness, and yield stability. Soil pH should ideally be between 5.5 and 6.8. Alkaline soils may block micronutrient uptake, which can cause yellowing leaves and poor fruit formation. Regularly testing soil and adjusting with elemental sulphur or gypsum can improve fertiliser efficiency in the long term.

Choosing the Best Fertilizer for Longan Tree Fruiting

To encourage heavy flowering and sustained fruiting in longan trees, you need to use a fertiliser tailored to subtropical fruit crops. While many home gardeners default to general-purpose NPK blends, these often contain excessive nitrogen, delaying flowering or encouraging vegetative growth at the expense of fruit. The best fertilizer for longan trees is one that:

Has a low nitrogen content to prevent overgrowth
Delivers a high dose of potassium and phosphorus for flower and fruit support
Includes calcium and magnesium to prevent fruit splitting and increase yield quality

Our recommendation: CompleteGrow NPK 4-18-38 + CaMg is a water-soluble fertiliser designed specifically for heavy fruiting crops like longans, lychees, mangoes, and stone fruits. It supports:

Flower spike development pre-season (Aug–Oct in QLD)
Strong fruit set and retention
Balanced mineral uptake for taste, texture, and colour

How to apply:

Young trees: Apply 25–30g monthly from spring to late summer, diluted and watered in
Mature trees: Use 80–100g quarterly (spring, early summer, late summer, early autumn)
Apply during early morning before heat stress, and always water deeply afterward

If your longan tree is in a pot, reduce rates by 50% and increase frequency to every 4–6 weeks. Keep an eye on leaf colour and flower bud formation as indicators of fertiliser success. Longans benefit from dry-season stress (reduced watering in late winter) to trigger flowering—avoid fertilising during this stress period to maximise blooming response.

Seasonal Schedule, Common Issues & Longan Tree Fertiliser FAQ

Fertilising a longan tree isn’t a one-size-fits-all activity. It’s a seasonal process that needs to reflect the tree’s stage of maturity, regional climate, and intended yield. Here’s a breakdown of the ideal seasonal fertiliser plan for longan trees in Australia.

Seasonal Fertiliser Guide for Longans (Australia)

Spring (Sept–Nov): Begin feeding with CompleteGrow 4-18-38 to stimulate flower buds and new root activity
Early Summer (Dec–Jan): Maintain potassium-rich feeding to encourage fruit set and retention
Late Summer (Feb–Mar): Apply final round of fertiliser to support fruit sizing and post-harvest recovery
Winter (Jun–Aug): Cease fertilising during cold or dry-season flowering induction

Common Fertiliser Mistakes

Overusing high-nitrogen fertiliser—leads to excessive foliage, no fruit
Fertilising during flowering season—can abort fruiting if overdone
Poor soil drainage—leads to nutrient lockout or root rot

Frequently Asked Questions

What is the best fertilizer for longan trees in pots?
Use a low-nitrogen, high-potassium blend like CompleteGrow 4-18-38 at half-strength monthly during active growth.

Can I use citrus fertiliser for longans?
Most citrus fertilisers are too nitrogen-heavy. Opt for a formula with higher potassium to support fruiting.

How do I boost fruit production on my longan tree?
Induce flowering by reducing water in winter, then feed with 4-18-38 as buds emerge. This supports flowering and reduces fruit drop.

When should I stop fertilising longans?
Stop all feeding by mid-autumn (late March) to allow trees to harden off before winter dormancy or flowering induction.