By Ching Ting Feng, Ph.D. , Plant Division Manager at JH Biotech, Inc.
A heat wave heats fruit directly. If intense light and hot air drive fruit surface temperatures past safe limits, then peel tissue can fail, and sunburn can show up as bleaching, browning, or necrosis. That damage is a mix of heat injury and photo-oxidative stress, where excess light energy drives reactive oxygen species (ROS).
Heat can also hit reproduction. If high temperatures land during bloom, then pollen performance and pollen-tube growth can drop, and fruit sets can suffer.
You can’t change the forecast, but you can change how well the plant holds function through the event. Start with what you control every week: nutrition. Then add canopy and surface tools that keep fruit cooler.
Why nutrition matters on hot, bright days
Under heat and high vapor pressure deficit, plants often tighten stomata to conserve water. If stomata clamp down, then CO₂ intake drops and photosynthesis slows right when the crop needs energy to defend tissues and finish fruit.
Potassium sits at the center of that response. Potassium helps regulate stomatal movement and water balance, and it supports the plant’s built-in stress defenses. Use tissue data to keep K in range, then correct deficits with a plan that fits your system.
Calcium plays a different role. If heat disrupts membranes and signaling, then calcium signals help trigger early heat-shock responses. Calcium programs can also support fruit quality, but they won’t replace cooling and shade.
Silicon fits the “helpful, context-dependent” bucket. Studies link silicon inputs with improved antioxidant activity or lower oxidative damage markers under abiotic stress in some settings. If silicon improves water status or antioxidant response in your system, then it can help the canopy hold function longer during heat.
Biostimulants can add another layer of support. Research on seaweed extracts and protein hydrolysates points to shifts in stress-response activity that can help the canopy hold function through hot, bright weather. If you use them, then treat timing as the main lever. Apply ahead of the peak heat window, then track the canopy response and fruit finish.
Keeping fruit cooler still matters
Nutrition supports the plant, but it doesn’t lower fruit temperature by itself. Sunburn risk rises fastest when fruit loses shade or takes a sudden jump in exposure. If you open the canopy right before a hot spell, then fruit that grows under the shade can scorch quickly.
Three practical tools target fruit temperature directly:
- Shade management. Keep coverage on the most exposed faces and rows when the long-range forecast turns hot.
- Cooling and netting (where used). These tools lower fruit surface temperature and radiation load.
- Particle films and sprayable protectants. White particulate films (kaolin/clay, calcium carbonate, or talc) reflect and scatter solar radiation and can reduce fruit surface temperature. They come with tradeoffs, including coverage, reapplication, and residue, so coordinate with your warehouse and follow label guidance.
A fast, nutrition-first checklist for heat events
48 hours before
- Confirm K and Ca status with the latest tissue data you trust.
- If K runs marginal, then prioritize correction pathways aligned with your program.
- Avoid introducing new chemistry right before the heat.
Day of / day after
- Protect shade on exposed fruit zones.
- If you use particle films or protectants, then apply early enough to matter and follow tank-mix limits.
After the event
- Re-check tissues and adjust, not guess.
- Document what worked: weather, timing, and pack out results.
Bottom line
Heat and intense sun punish fruit through temperature and oxidative stress. If you keep potassium, calcium, and other essentials in range, then the canopy can stay productive longer and fruit can handle stress better. Pair that foundation with shade and surface-protection tactics that lower fruit temperature, and you’ll reduce the odds that a heat week turns into downgraded bins at harvest.
JH Biotech, Inc. develops plant nutrition and biological products for commercial agriculture, with categories that include foliar nutrients, soil amendments, and biostimulant materials such as seaweed extracts and humic substances. For growers and advisors, the goal stays simple: use data-driven nutrition to support plant function when conditions turn stressful.