Preparing Trees for Winter:

To Water or To Not Water

Our lives are full of sayings, traditions, old adages and clichés.  We even have the modern term of “urban legend” that some persons use to describe things that sound good but really aren’t quite correct.  Most people also like things to be simple and automatic so that they don’t have to think too much.  So it is very easy to read or listen to simple phrases such as “you must water your trees deeply before winter” and embrace that idea because it is simple and “seems” to make sense.  Well, as with most oversimplified sayings, that one is only partially correct.

The truth of the matter is that some trees benefit from watering in late fall while other trees don’t benefit at all and a few trees can even be damaged or killed by wet soil in the fall.  “Oh this is much too complicated” you may say.  Why can’t I just pretend all trees are the same and treat them all the same way.  Well, the problem is not really all that complex and it shouldn’t take too many words to explain.

Evergreen trees retain their leaves or needles all through the year and so they can use water all through fall and into winter.  They can suffer quite a bit if they are in dry soil during winter.  On the other hand, deciduous trees, those which lose their leaves in fall have very little water use during late fall and winter and they do not usually benefit from moist soil while they are dormant.  So there it is, in quite a simple form, evergreens may need fall watering, deciduous trees generally do not.

If we have a good amount of rainfall during October and November then generally no additional water needs to be applied, even to evergreens.  But if we have dry conditions during mid to late fall then it would be a good idea to water the roots of evergreen trees once or twice before winter.  Again, this is a bit of an oversimplification, the only way to really know whether to water or not is to test the soil moisture, which is actually quite easy to do.

A very frequent mistake many people make is to water in fall at the base of the tree.  This does almost no good because most of the absorbing roots of trees are out away from the trunk.  Only on young, recently planted trees would watering at the base be of much benefit.  Trees that have been growing for a while will have roots out many feet away from the trunk.  And large old trees will have roots that likely fill your entire yard and maybe part of your neighbor’s yard as well.  The best way to water  tree roots is to use a sprinkler just like you were watering the lawn.  Obviously you can’t use an automatic in-ground sprinkler system because those will all have been shut off for the season by then.  Just use a portable sprinkler on a hose.  Water the entire area around the tree at least as far out from the trunk as the tree is tall.  That means if you have a 50 foot tall tree you should water at least 50 feet around it on all sides.

And now, just to shoot down another of those old legends about watering trees, I will say that you don’t need to water trees “deeply” for it to be beneficial.  The reason for not needing to water deeply is that on most trees 90% or more of the absorbing roots are in the top 18 inches of soil.  In general, there is no need to apply more than about ½” of water to trees in fall.  Any more is simply wasting water and may actually damage or kill some trees.  If the soil around evergreens seems dry after one fall watering then simply do another moderately deep watering.

A few tree species can actually be damaged or killed by overwatering in the fall.  The most common victims are young and recently planted maple trees.  Many young maples die every year in this area and the most common cause is overwatering in fall which may kill the roots.  After maple trees are 8-10 years old they do not seem to be bothered as much by fall watering.

So, to sum it all up, evergreen trees may benefit from watering in the fall if the soil is dry but deciduous trees usually do not benefit.  If you have a yard or an area with both types of trees then check the soil moisture and if it is dry then apply a moderate watering for the benefit of the evergreens.

Robert Pitman

Extension Horticultural Assistant