Floral Freeze Tolerance and Freezing Conditions
Blueberry floral bud, flower,
and fruit sensitivity to freeze has been extensively researched from
which university extension systems have published guides on floral
growth development. Based on this research, cold sensitivities have
been suggested based on the phenological stage. There are nine stages
of flower bud development from tight bud to petal fall, at which point
the small green fruit is sensitive to 0 °C (32 °F). Bud swell (stage 2)
indicates the plant has deacclimated, and at bud break (stage 3), the
flowers are sensitive at −7 °C (19 °F). Tight cluster (stage 4) is
sensitive to −7 to −5 °C (20 to 23 °F). As the flower develops toward
bloom, three stages are noted—early pink (stage 5), pink (stage 6), and
late pink (stage 7)—which can tolerate −4.4 to −2.8 °C (23 to 27 °F).
Floral full bloom is when the corollas are fully expanded (stage 8),
which can tolerate −2.2 (28 °F). Once the petals fall (stage 9), freeze
damage will occur at 0 °C (32 °F). Floral bloom for SHB is not strictly
regulated by chill hours and even with sufficient chill, SHB will bloom
unevenly. This is observed by the variation of bloom progression within
a bush, causing growers to estimate the cold sensitivity of the crop.
The appropriate response is dependent on the growers’ desire to salvage
the crop.
![Credit: Erick D. Smith, University of Georgia Tight bud (stage 1), bud swell (stage 2), and bud break (stage 3)](images/Blue57.jpg) Tight bud (stage 1), bud swell (stage 2), and bud break (stage 3) Tight
bud and bud swell can tolerate cold temperatures of −12 to −9 °C (10–15
°F). Bud break is more sensitive to cold, where at −7 °C (20 °F),
damage can occur. ![Credit: Erick D. Smith, University of Georgia Tight cluster (stage 4) and early pink bud (stage 5)](images/Blue56.jpg) Tight
cluster (stage 4) and early pink bud (stage 5), which are cold tolerant
to −5 to −4 °C (23–25 °F) and −4.4 to −2.8 °C (24–27 °F), respectively. ![Credit: Erick D. Smith, University of Georgia Pink buds (stage 6) and late pink bud (stage 7) stages,](images/Blue55.jpg) Pink
buds (stage 6) and late pink bud (stage 7) stages, which are cold
tolerant to −5 to −4 °C (23–25 °F) and −4.4 to −2.8 °C (24–27 °F),
respectively. ![Credit: Erick D. Smith, University of Georgia Full bloom (stage 8) and petal fall (stage 9)](images/Blue54.jpg) Full bloom (stage 8) and petal fall (stage 9), which are cold tolerant to −2.2 °C (28 °F) and 0 °C (32 °F), respectively.
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