Searing Temperature Calculator

What the Garden Searing Index represents

This calculator combines a humidity-based heat index with sunlight and wind adjustments to estimate canopy heat load. The output is an adjusted index plus thresholds for moderate and severe stress. Use it as a decision meter: when the index nears the moderate threshold, start protection before leaf scorch appears. During heat waves, a 2–3°C shift can change the risk category, so refresh readings near late morning and mid‑afternoon.

How humidity changes plant cooling capacity

Plants cool themselves through transpiration, which depends on how easily moisture evaporates from leaves. When humidity is high, evaporation slows and leaves can run hotter than the air, especially in still conditions. When humidity is very low, water loss accelerates and drought stress rises unless soil moisture is adequate.

Sunlight, wind, and canopy microclimate

Full sun adds radiant heat that can push tissue temperature above air temperature, especially on broad leaves. Light wind often reduces the warm boundary layer around leaves, improving cooling; however, hot, dry wind can increase water demand. Shade cloth (30–50%) can cut peak load in exposed beds, while spacing and airflow reduce hot spots near walls.

Soil moisture, mulch, and irrigation timing

Soil moisture influences whether plants keep stomata open for cooling. As soil dries, stomata close and leaf temperature rises. Deep watering early supports steadier moisture through midday heat, while quick sprinkling can leave roots shallow. A 5–8 cm mulch layer reduces surface heating and slows evaporation. On the 0–100 scale, many gardens aim for 45–65 in summer, then adjust for soil texture and pots.

Interpreting thresholds and planning actions

Risk scores rise when the adjusted index exceeds the moderate threshold and intensify with longer exposure and drier soil. Moderate risk suggests tighter watering and partial shade; high risk favors midday shade, less pruning, and pausing fertilization. Extreme risk calls for immediate protection of seedlings and containers, and frequent checks for wilting, sunscald, or blossom drop. Export results to CSV or PDF to compare days.

FAQs

1) Is this a soil temperature tool or an air heat stress tool?

It is a plant heat stress tool based on air conditions and exposure. Soil moisture is used as a stress modifier, not as a direct soil temperature measurement.

2) What readings should I enter for best accuracy?

Use a thermometer and humidity reading near the plant canopy, ideally in the shade. Wind should reflect your bed’s airflow, not a distant weather station value.

3) Why can full sun feel hotter than the heat index?

Heat index focuses on air temperature and humidity. Full sun adds radiant energy that can elevate leaf and soil surface temperatures beyond air-based comfort measures.

4) When should I apply shade cloth?

Consider it when the adjusted index is near the moderate threshold for sensitive plants. Apply before peak midday sun, and remove or loosen it when cooler conditions return.

5) Does wind always reduce scorching risk?

Not always. Gentle wind can cool leaves, but hot, dry winds can increase water loss. Pair windier days with deeper watering and windbreaks for delicate seedlings.

6) How do I use custom thresholds?

Select Custom thresholds and enter your preferred moderate and severe values in °C. This is useful for greenhouse crops, regional varieties, or plants with known heat tolerance ranges.