There's a chill creeping into the air. The leaves are changing colors. Winter is just around the corner. Now is the time to think about properly watering your trees in autumn to help ensure against damage in the winter.
In the middle of winter, the ground is frozen. Trees are not able to access water, so it is important that you are watering your trees in autumn as necessary. Watering your trees in early autumn is different than late autumn, so water accordingly.
In early autumn, you should stop watering your deciduous and evergreen trees. Do not worry about watering until the leaves have fallen from the deciduous trees.
The trees are still growing in early autumn and watering will encourage new growth. If a frost comes when there is new growth on the tree, it will be damaged.
Once the deciduous trees have lost their leaves in late autumn, it is time to start watering again. Evergreen trees will definitely need to be watered before winter - since they never lose their foliage and go into full dormancy, they will constantly be losing water throughout the winter.
By late autumn, the tops of the trees have gone dormant, so they will not produce new growth. The tree is busy moving nutrients around in preparation for dormancy.
Water deeply (at least 1-2 feet deep at a time) until the ground is frozen. Deep watering encourages proper root growth so that the trees will be able to access water farther down in the soil.Young trees, especially, need lots of water to establish roots in preparation for winter. Newly planted trees should be watered at the base, while more mature trees should be watered at the dripline.
You can keep watering trees in late autumn as long as there is no snow cover and the air temperature is above 45 degrees. Trees in milder climates should be watered throughout the winter as needed, though usually the rains will suffice.