Except for cool-season vegetables and lawns, most plants will be dormant or growing very slowly during this time of year. Fertilizing is most beneficial when plants are actively growing or developing fruit or flowers. Even citrus which ripens during the winter is best fertilized for the last time of the year before October 1. Some California native plants are active in the winter, but they evolved in our native soil and generally do not need supplemental fertilization. Fertilizing plants now will create tender new growth right before the risk of frost. Some nutrients cannot be taken up efficiently by plants during cold weather. The excess can leach into the groundwater or run off and reach the bay. Ultimately, using unneeded additives is a waste of resources and money.
More Information: Dormant Season