The 2024–2025 durian season in many Central Highlands areas has raised serious concerns among growers. Some orchards experienced delayed flowering, prolonged flowering periods, mixed vegetative shoots with flowers, and difficulties in controlling fruit set. One of the most frequently mentioned causes is prolonged cold weather coinciding with the bud initiation and water stress (drying) stages.

However, while weather is beyond our control, technical management in response to weather conditions can be proactively adjusted. Understanding the physiological nature of the durian tree is the key to minimizing risks and stabilizing production.

1. The Role of Cold Season in Floral Bud Differentiation of Durian

In the Central Highlands, early dry-season cold weather is normally considered a natural favorable condition for floral bud differentiation in durian, acting as a “physiological trigger.”

Lower nighttime temperatures and a large day–night temperature difference help to:

  • Suppress vegetative growth

  • Promote the transition from vegetative to reproductive growth

At this stage, a chain of physiological reactions occurs:

  • GA (gibberellins – growth-promoting hormones) decrease

  • ABA (abscisic acid – growth-inhibiting hormone) increases

  • The ABA/GA ratio rises above the critical threshold

  • Vegetative buds convert into reproductive buds

These are ideal conditions for floral bud differentiation in durian.

2. Prolonged Cold and the “Physiological Lock” Phenomenon

When cold conditions persist for an extended period and coincide with sensitive physiological stages, trees may become excessively inhibited beyond their tolerance threshold.

Instead of transitioning smoothly, the tree may enter a state known as “physiological lock” or deep dormancy, resulting in:

  • Slow formation of floral buds

  • Incomplete bud differentiation

  • Uneven flowering or mixed flowering with vegetative shoots

This occurs due to:

  • Strong reduction in enzyme activity

  • Slower metabolic processes

  • Prolonged reduction of root activity

  • Disruption in hormone transport

Once again, the problem is not whether cold is good or bad, but how growers prepare and adjust technical practices when prolonged cold occurs.

3. Flower Induction Means Creating Conditions for Phase Transition — Not Forcing Flowers

“Flower induction is not about forcing the tree to bloom, but about creating the right conditions for the tree to naturally shift its physiological phase.”

Floral differentiation is an internal biological decision, strongly influenced by:

  • Temperature

  • Water status

  • Root growth rhythm

  • Hormonal balance

Therefore, growers should prepare proactively instead of waiting until adverse weather occurs. Proper management should be implemented early through the following steps:

Step 1: Preparation from the Last Leaf Flush Before Cold Season

The leaf flush prior to the cold season determines the tree’s flowering potential.

At this stage, the goal is not to push vigorous growth, but to:

  • Build a strong and stable root system

  • Maintain thick, durable leaves without excess nitrogen

  • Accumulate balanced nutrient reserves

Special attention should be given to:

  • Phosphorus and potassium for energy storage and nutrient utilization

  • Calcium to strengthen leaf and root tissues and improve cold tolerance

Healthy mature leaves help the tree pass through the cold season with stable physiology.

Step 2: Flexible Water Stress Management During Prolonged Cold

Water stress (drying) is an important technique to support flowering. However, under prolonged cold conditions, excessive and continuous water stress should be avoided.

When night temperatures drop:

  • Root activity is already naturally reduced

  • Overall growth is already suppressed

If strong water stress continues:

  • The tree may become overly physiologically inhibited

  • Enter a “double stress” condition (cold + drought)

  • Floral bud differentiation may fail to complete

In years with prolonged cold, reduce the intensity of water stress and adjust based on tree response rather than following rigid schedules.

Step 3: After Cold Period — Regulate Growth Rhythm, Do Not Rush to Force Buds

After the cold period, durian trees tend to flower naturally if floral buds were well formed beforehand.

At this stage:

  • Do not rush to apply bud-forcing sprays

  • Focus on regulating growth rhythm

  • Avoid sudden vigorous vegetative growth

  • Prevent early leaf flushing

  • Maintain uniform flower emergence

Foliar sprays should aim to stabilize physiological status, not to force flowering, such as:

  • Calcium (to stabilize cell structure)

  • Amino acids (to reduce stress)

  • Low-dose micronutrients to keep the tree in balance, not to stimulate growth

Step 4: Early Branch Girdling or Light Branch Pruning After Cold Season

Early branch girdling or light pruning after the cold season is a mechanical practice that is:

  • Easy to perform

  • Low cost

  • Highly effective physiologically

The objectives are to:

  • Release dormant buds

  • Reactivate buds suppressed by cold

  • Promote more uniform flowering

4. Important Practices to Avoid Under Adverse Weather Conditions

During unfavorable weather, avoid the following common mistakes:

  • Excessive use of nitrogen fertilizers and growth stimulants

  • Repeated heavy bud-inducing sprays immediately after cold periods

  • Applying the same technical formula every year regardless of weather variation

These interventions can disrupt the tree’s physiological rhythm, increasing risks of flower drop and early fruit drop later on.

Conclusion

Adverse weather may recur, but risks can be significantly reduced if growers prepare early and understand plant physiology correctly.

  • Cold season is a natural advantage of the Central Highlands

  • Prolonged cold is a technical challenge, not a disaster

  • Correct timing, proper intensity, and early preparation lead to stable and sustainable flowering

Wishing all growers a successful season.

Technical Department
Sitto Vietnam Co., Ltd.