Critical Spring Temperatures

Critical cold temperatures for blueberries.

1 – Dormant or tight bud 2 – Bud swell 3 – Tight cluster  4 – Early pink bud
Tight bud Budswell Tight cluster  Early pink bud
Plant part: Flower bud.
Description: No visible swelling of the fruit buds. Bud scales tightly closed. No visible signs of growth.		 Plant part: Flower bud.
Description: First sign of   growth as plant growth begins in the spring. Visible swelling of the flower buds; outer bud scales begin to separate at the tip revealing paler interior bud scales. This bud stage can usually tolerate cold temperatures of 10 to 15°F (-12 to -9°C).		 Plant part: Flower.
Description: Individual flowers are distinguishable in the flower cluster. This bud stage can tolerate 20 to 23°F (-7 to -5°C).		 Plant part: Flower. Description: Expanding flowers are readily visible and have separated. The pink corolla tubes (petals) are short and closed. This bud stage can tolerate 23 to 25°F (-5 to -4°C).
5 – Late pink bud 6 – Full bloom 7 - Petal fall  
Late pink bud Full bloom Petal fall  
Plant part: Flower.
Description: Individual flowers fully developed. Expanded corollas are now white but still closed. This bud stage can tolerate 24 to 27°F (-4.4 to -2.8°C).		 Plant part: Flower.
Description: Most of the flowers on the bush have opened. The bloom stages can tolerate 28°F (-2.2°C).		 Plant part: Flower.
Description: The corolla tubes are falling off the flowers, revealing small green fruit. This is the most vulnerable stage to freeze injury. Damage can occur at 32°F (0°C).		  
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