Hardening index

If the hardening index (unitless, 0.00 - 2.00; HardeningIndex) is lower than 1.00, it increases only if daily average crown temperature is higher than -1°C. In case average crown temperature is lower than 8°C, HardeningIndex is calculated using the following equation:

where Tavg_crown (°C) is the average daily crown temperature.

If Tmax_crown is higher than 10°C, de-hardening conditions occur and the HardeningIndex is calculated as follows:

Also if HardeningIndex is between 1.00 and 2.00, the crop can be subject to hardening or de-hardening conditions, respectively if Tavg_crown is ≤ 0°C or Tmax_crown is higher than 10°C.

In the first case (Tavg_crown is ≤ 0°C), HardeningIndex is increased by 0.08333 (12 days of hardening are enough to reach stage hardening index = 2).

In the second case (Tmax_crown is higher than 10°C),

In practical terms, for each degree above 10°C, HardeningIndex decreases of 0.04.

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