Questions about dormancy in California almonds
Once they have the capacity to grow, once endodormancy is over, buds need a certain amount of heat units to begin growing. This dormancy is imposed by external conditions and called ecodormancy by the plant physiologists. I’ll bet, as of Jan. 15, that almonds in the Central Valley have passed through endodormancy and are in ecodormancy. We are currently running between 600-800 hours under 45oF in the Sacramento and San Joaquin Valleys (check for chilling accumulation levels throughout CA at: fruitsandnuts.ucdavis.edu/Weather_Services). If endodormancy has passed and the chilling requirement met, buds on a shoot cut from the orchard and placed in water in a warm place will “break”, will expand and grow. The more chilling, the shorter the heat accumulation needed to bloom.
So, after all that, what about the questions posed at the beginning of this post?
- Are trees with leaves remaining in January less dormant or somehow different than trees that are defoliated or naturally bare by January? No, they should be the same.
- Doesn’t spraying trees with zinc in the fall make them dormant faster? They don’t have leaves… They don’t become dormant faster. Endodormancy is triggered by shorter day length and/or cooler temperatures, not the absence of leaves.
- Do trees with some leaves left in the canopy in January accumulate less chilling than trees with no leaves in December? No, chilling accumulation is related to temperatures and conditions in the buds, not the leaves.
Note, removing leaves in the fall or winter, is a part of an integrated disease management program in almonds.