🍓 Strawberry quality decreased because of heat in greenhouse?

A 2025 study suggests an easy and low-cost solution.

High-temperature stress is one of the fastest ways to lose flavor, size, and color.

In a recent greenhouse trial, foliar spraying strawberries with a low NaCl (salt) solution during fruit fill did three things under heat spikes (>25 °C):

1️⃣ Kept the plants working
• Photosynthesis rate, stomatal conductance, and transpiration all increased compared to control (without foliar salt spraying).
• Leaves accumulated more N, P, K, Fe, Zn, and Ca.

2️⃣ Improved marketable fruit
• Average berry weight increased ~35%.
• Color improved.
• Berries were sweeter: total soluble sugars rose ~15%.
• Acidity dropped, which means better perceived flavor.
• Vitamin C, phenolics, and flavonoids increased, boosting nutritional value / antioxidant capacity.

3️⃣ Did it without salting the root zone
• Instead of adding salt to the substrate and risking long-term salinization, Na and Cl were supplied to the canopy. Leaves took up Na (supporting photosynthesis and water status), and fruits accumulated Cl, which strongly tracked with better size, sugars, and color.

✅ Advantages:

• During heat spikes, plants maintain photosynthesis and fruit quality.
• A controlled foliar salt spray is low-cost and operationally simple.
• This approach targets the plant, not the soil — important if you’re worried about long-term soil salinity.

💡Practical takeaways you can test in your facility:
• Timing: Start at fruit set, continue through ripening in the high-temperature window. Daily morning spray was used in the trial.
• Dose: Stay in the 10–15 mM NaCl range. Above 20 mM, benefits flattened or reversed. Don’t jump higher.
• Start small: Run it on a contained block first and monitor leaf burn, fruit mineral profile, postharvest behavior, and customer taste response. The study notes we still need data on shelf life.

Note: These results were obtained with the strawberry cultivar Benihoppe. Your cultivar may respond differently, but it is worth trying.

📚 Source: Lu et al. (2025). Low-concentration NaCl foliar spraying enhances photosynthesis, mineral concentration, and fruit quality of strawberry during greenhouse high-temperature periods. BMC Plant Biol, 2025 Apr 16;25(1):487

Dr. Michele Grieco turned his plant biology expertise into Plant Monitor - affordable monitoring apps bringing research-grade measurements to small greenhouses and vertical farms.

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