Almonds, like other deciduous fruit trees, require sufficient amounts of cold temperatures in the winter to break the “rest” period. The exposure to sufficient winter cold is necessary for normal growth of flower and shoot buds. The cold temperature requirement is called the chilling requirement which is the accumulation of temperatures below 45 degrees from Nov. 1 to Jan. 15. The chilling requirement for almonds is 200-300 hours.
In Kern County, we have been accumulating an average of 700 chilling hours in the last five years. Also, in these years almond orchards have produced record crops. However, for this dormant season (Nov. 1 to Jan. 15) 522 chilling hours were accumulated. This means that the cold temperatures from 2005-06 are below normal.
One of the lowest chilling years on record was 1995-96 in Shafter. This season only accumulated 336 chilling hours. The distribution of these hours was the following: November 81, December 138 and January 117. In comparison, the distribution of the chilling hours for the 2005-06 was the following: November 161, December 240 and January 111. The data shows that there were a higher number of chilling hours in the months of November and December of 2005-06 than in the same month of 1995-96 season. Therefore 2005-06 was a better chilling season than the 1995-96 season. This may be good news because both county and state almond yields were a disaster in 1996. Kern County average production was 960 meat pounds per acre and the state production was 366 million meat pounds.
In addition to low chilling hours in 1995-96, there were other factors that may have contributed to the low production. There was mild bud drop in Mission, Price, Fritz and Carmel and a prolonged bloom period for Sonora, Monterey, Wood Colony, Nonpareil, Padre and Butte. Varieties whose bloom was delayed were Carmel and Mission. Perhaps, the factors that contributed the most to the low yields were the high temperatures in mid-February and mid-March.
It is hard to predict what impact a low chilling season like 2005-06 will have on yields. However, based on past history, varieties that have a low chilling requirement will come into bloom much earlier than normal. The bloom period within varieties and between varieties also can be expected to be extended, creating cross-pollination problems. The timing of bloom sprays may be difficult to do. In addition, some bud drop may take place in Mission, Price, Fritz and Carmel.