How to reduce heat from your structures during the warmer months to help maintain good pollination and fruit size

It was a real pleasure and privilege to co-present with Bert Van Giffen from Bert’s Berry Farm at the recent Strawberry New Zealand Conference. Our presentation focused on the importance of reducing heat in tunnels and greenhouses, and the positive impact this can have on pollination, fruit size, and overall crop quality.

How do we control air temperature?

Every growing setup and location is different—meaning there is no “one size fits all” solution. Tailored strategies are required. The key message we wanted to emphasise was simple: test and trial different options to find what works best for your operation.

Shading products and diffused coatings are available and should be considered by all growers, even those using plastic-covered tunnels. When applied at the correct times of year, they can help regulate air temperature and protect crops from the damaging effects of heat.

Why temperature control matters

High temperatures can dramatically affect a strawberry plant’s ability to set fruit and maintain fruit size. The longer you can reduce the negative impact of heat stress, the longer you can sustain consistent production, quality, and shelf life.

High temperature directly impacts:

• Fruit size
• Fruit setting
• Fruit quality

Growing speed: light vs. heat

There’s often a misconception that higher temperatures automatically lead to faster growth and more production. This is not the case. Light, not heat, is the key driver of production (to a point).

• The more light the plant receives, the more energy it can absorb, and the higher the potential yield.
• However, when plant temperatures rise too high, cells divide more rapidly but with less energy available per cell—resulting in smaller cells and, ultimately, smaller fruit.

In other words: light is more important than heat, provided it is managed carefully. Strawberries generally require between 600–700 W/m² of light, while New Zealand conditions often exceed 1,000 W/m². This makes it even more important to use tools that can temper excessive light and heat.

Managing excess light and heat

Of course, too much light can also be a problem. As highlighted in the chart provided by Signify’s Aart Slobbe, when high light levels are coupled with high temperatures, plant stress can increase dramatically.

A layered approach to coatings and shading can be very effective:

• Early in the season: apply a reflective coating to reduce heat while still allowing light through.
• In peak summer: add a second, different shade coating designed to reduce both light intensity and heat load.

This strategy provides flexibility and ensures plants remain productive, fruit quality is protected, and crops maintain resilience throughout the hottest months.