Although we have received a bit of rain this past week, some inquiries about applying a winter irrigation have been made. There is concern that since the soil is dry from lack of rains, that the trees will be stressed, negatively affecting the fruit bud.
Briefly, an irrigation in December to alleviate water stress in dormant trees is not needed in most cases. In order for water to move into the tree’s branches, it needs the “pull” created by the leaves (transpiration). Without leaves, the water may move into the roots, up a few inches into the wood through capillary action, but not into the branches and buds within the mid to upper canopy of the tree.
The only exception may be in a situation of extreme drought, in which the trees have had considerable seasonal stress and complete defoliation. This occurs rarely in California.
There are other reasons to apply a winter irrigation. These include refilling the soil profile to help with irrigations scheduling in the spring, and watering in an applied pre-emergent herbicide.