Early bud break of almonds

A farm call last week in the Livingston area brought up some nice discussion regarding early bud break of trees. All of the growers varieties had buds that appeared to be "pushing." Most notable were trees within the Sonora variety. As seen in figures 1 -3, varied bud stages were present, including green tip through the popcorn stage (For more information, please see the article The Seasonal Patterns of Almond Production). Seeing this, the grower was having concerns about the possibility of an early bloom.
Figure 1: Almond buds beginning to break showing "green tips."

Figure 2: Early bud break of a Sonora tree with the blossom in the "Popcorn" stage.

I doubt that we will have an exceptionally early bloom. Conversations with long time growers and consultants have indicated that this "pre-bloom bloom" can occur with early varieties. It has also been observed that tree buds will swell quickly, appear that they are going to bloom, only to remain dormant for several more weeks. I would guess that we are still looking at a mid to late February bloom. Remember to south San Joaquin Valley growers: you guys are always a week or so ahead of central San Joaquin valley.

Please let me know if you are all seeing/thinking something different.

Since we are on the topic of bloom, lets consider a few things that affect bloom timing.
Chill hours: Required chill hours have been accumulated. Across the valley, the minimal hours observed have been around 700 - almonds need 500-600. Broadly, chill hours are the tree's self protecting mechanism that requires it to be exposed to enough hours of cold weather (<45 degree F) in order to prevent it from blooming at the wrong time. If these hours are not met, poor bloom, deformed leaves, and lack of growth will occur. Since the required hours are lower than many other tree crops, very rarely does this occur. Once chill hours are met, the break of almond dormancy is often delayed by soil and air temperatures, as well as the photoperiod.

As growers, we can not directly change the temperatures and amount of sunlight/darkness in which trees are exposed. We can, however, use some farming practices to change the "micro-climate" of the orchard. It has been observed that blocks that have been sprayed with dormant oil or calcium nitrate tend to push a few days earlier than untreated blocks. Shooting from the hip, I would guess that dormant oil increases the boundary layer temperature of the tree, making it "feel" warmer than actual ambient air temperature. So, if chill hours have been accumulated, and the nights are short enough, the tree would bloom since it is now warm enough.

Even though calcium nitrate gives a similar affect on bloom timing, I would suspect that it works in a different way. Even though I am not 100% sure, I would guess that calcium nitrate increases the amount of solutes within the tree's cells, triggering cell expansion through changing the osmotic potential, and thus triggering the tree to bloom by causing the required hormone imbalance. It is possible that dormant oil may do something similar, but I dont know (and I cant find a resource quick enough to answer my own questions)- so please let me know if it does.

Another way we can change the "micro-climate" is by increasing soil temperature. Often, orchards that are irrigated in the dormant season to refill the soil profile often bloom earlier than those that have a unfilled soil profile. This affect is most likely due to the slight warming affect that moisture brings to the soil. Typically we expect winter rains to refill our soil profile, but this does not always happen - the 2007/8 and 2008/9 winters are good examples. In years where we are short on rain, a pre-irrigation can help push the trees to bloom.

I hope this provides some insight for the upcoming season.