Generally speaking, you can stop watering at the same time deciduous trees begin dropping their leaves – usually mid-October in our area. When the daily high temperatures are less than 70 degrees most plants begin to become dormant in preparation for the winter season. Normally supplemental watering is not needed after this point.
There is one exception with newly installed plants. Occasionally watering is needed if we have experienced a fall drought. In these cases, we would recommend watering weekly into mid December. Fortunately, this is not the situation this year.
For established landscaping, we recommend one watering before the end of December to prevent winter desiccation.
The best way to prevent winter injury is to have healthy, moist plants going into the more severe cold period.