Managing Heat Stress in Nursery Environments

Heat stress is one of the most significant and increasingly common challenges for production nurseries and retail garden centres in NSW and ACT. Higher summer temperatures, longer heat events and more frequent extreme days affect plant quality, labour productivity and operational costs. Effective heat management is a core capability for maintaining stock consistency, protecting staff and achieving reliable plant performance.

Root zone temperature is often the hidden factor. In black containers, media can exceed ambient air temperature by 10 to 20 degrees,  directly affecting nutrient uptake and growth. Australian university research consistently shows that reducing root zone temperature improves performance and reduces losses.

Shade Design that Works

The most effective shade strategies consider both percentage and placement.

Shade Cloth Selection:

• 30 to 40% for hardy full sun stock
• 50 to 70% for young or heat sensitive species
• 70 percent plus for propagation

Balancing protection without restricting growth is essential.

Shade Structure Orientation:

East–west orientation reduces morning and afternoon heat intensity. Ensure ventilation along the sides and at the roof apex to allow heat to escape.

Movable Shade Systems:

Retractable or adjustable shade systems help nurseries respond quickly to extreme temperature spikes. Studies show they improve summer uniformity and reduce losses.

Water Management and Irrigation Adjustments Irrigation requires careful management during high heat. Irrigation Frequency: Short, frequent cycles help maintain moisture in the upper root zone without creating waterlogging. Timing: Early morning irrigation reduces stress before peak heat. In extended heat events, a light afternoon cycle may be required to stabilise plants.

Monitoring pH and EC:

Heat influences nutrient uptake, so regular monitoring prevents deficiencies and imbalances. This aligns with recommendations from NSW DPIRD and university agronomy programs.

Air Movement and Ventilation

Increasing airflow lowers leaf temperature and improves evaporative cooling.  Options include:

• Horizontal airflow fans
• Ridge vents in greenhouses
• Roll up curtains or raised sides in polyhouses

Even moderate airflow can significantly reduce heat load during extreme days.

Root Zone Protection

 Protecting the root zone is essential for resilience. Strategies include:

• Avoiding dark ground surfaces that absorb heat
• Using insulating layers between the ground and pots
• Pot-in-pot systems for sensitive crops
• Wider spacing to improve airflow around containers

These adjustments reduce heat accumulation and support stronger root development.

Staff Safety and Workflow Adjustments

Heat stress management must include worker safety. Best practice includes:

• Rotating staff through shaded or indoor tasks
• Easy access to cool drinking water
• Scheduling heavy tasks earlier in the day
• Using heat alert systems or apps
• Ensuring PPE is suitable for hot conditions

These steps align with SafeWork NSW guidance for outdoor workplaces.

Emergency Response During Heatwaves When temperatures exceed thresholds or forecast conditions change rapidly, activate a clear response plan: Increase temporary shading Apply short cool down irrigation cycles Move high value or sensitive stock to protected areas Adjust dispatch schedules to minimise heat exposure on trucks Increase monitoring of at-risk crops

Documenting this plan ensures consistency and reduces losses.

Why Proactive Heat Management Matters

Proactive heat strategies support:

• Higher saleable stock percentages
• Lower losses in propagation and finishing areas
• Better staff wellbeing
• More predictable production schedules
• Reduced water and energy waste

Industry research consistently links environmental control to improved margins, demonstrating that heat management is both a horticultural and business priority.