Spring critical temperatures

Critical cold temperatures for blueberries.

1 – Dormant or tight bud

2 – Bud swell

3 – Tight cluster

Tight bud Budswell Tight cluster

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).

4 – Early pink bud

5 – Late pink bud

6 – Full bloom

Early pink bud Late pink bud Full bloom

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).

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).

7 - Petal fall

Petal fall
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).