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Figure 6. Full Bloom

Every spring season, peach growers in Alabama have concerns about the occurrence of potential frost or freeze events and the potential damage to the growing peach crop. To help predict the outcome of an early spring freeze event, a grower should consider the temperature at which flower buds are injured. This depends primarily on their stage of development among other factors.

In general, buds are most cold hardy during the winter when they are fully dormant. As they begin to swell and the blossoms begin to develop, they become less resistant to freeze injury. Resistance to freeze injury varies not only between cultivars and orchards, but also within trees. Buds that develop slowly tend to be more resistant at lower temperatures.

Figures 1 – 8 illustrate the peach bud stage of development. The table shows the average temperatures required to kill 10 percent and 90 percent of developing peach buds if they are exposed for 30 minutes.

 

Peach Buds Stage of Development

Peach Buds Stage of Development10% kill (F degree)90% kill (F degree)
First swelling 181
Calix Green 215
Calix Red 239
First Pink 2515
First Bloom 2621
Full Bloom 2724
Post Bloom 2825

 

Minimize the Potential for Cold Damage

  • Choose a good site prior to planting the orchard. Use high ground that allows for easy drainage of cold air off the site.
  • The choice of the proper cultivars is critical, including sufficient cold hardiness for the region in which they will be grown as well as a suitable chilling hour requirement.
  • The timing of dormant pruning is important. If a frost or freeze event is expected, it is best to delay dormant pruning as long as possible.
  • Orchard floor management can significantly influence springtime orchard temperature. Soil that is not covered with vegetation can absorb more heat during the daytime and give off more heat in the nighttime than soil that is covered. Similarly, moist soil is also warmer at night than dry soil.
  • During cold nights (radiational freeze), wind machines can be used to stir warm air above the orchard.
  • The most difficult freeze conditions to manage occur during an advective freeze (when it is very cold in combination with high wind speeds).
  • Using orchard heaters, burning straw bales, etc. may be helpful.
  • Following pollination, once fruit have set and they are beginning to grow, cold damage can still occur.

Sources

Penn State Extension: Orchard Frost – Critical temperatures for various fruits, Oct. 2014.

Clemson University Cooperative Extension – Frequently Asked Questions

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