Kelly asked me recently if we should write an article about watering our trees. Now that a storm is just about here, I wonder if I should post this; but I don’t know for sure how much rain we will get until we get it and these winter dry periods happen from time to time so I will go ahead. Perhaps publishing this will help to ensure that we get more rain!
Normally I would not recommend irrigation during the winter; however, there had been such a long rainless period I started to wonder.
For sure, newly planted trees, should be watered to maintain ideal soil moisture conditions in the container media (which dries out much more rapidly than the native soil; this time of year within a few days) and the surrounding soil. Most soils will take much longer to dry out – perhaps 7-14 days at 6″ depth depending upon soil type, mulching and other factors.
For established trees, whether or not the tree experiences stress would be dependent upon water use and rooting depth. Deciduous trees should need little water this time of year (however, having a fully (water) charged soil to the depth of the root system would be important in the spring) and evergreen trees are going to use water slowly this time of year. One could monitor for wilting of evergreens. However, it might be good insurance to irrigate once for peace of mind if nothing else.
UCD Professor Alison Berry irrigated her redwoods. UC Davis Irrigation Specialist Larry Schwankl provided the following response when I asked if we should water our trees:
“I would definitely recommend folks with trees put on an irrigation. It is important that there be sufficient moisture in the soil when the first root activity (some folks call it a root flush) begins. For some trees this happens before you see activity above-ground. You are correct that this time of year there is low ET but what irrigations now are doing is setting the tree up for healthy growth once activity starts. Agricultural tree growers are starting to irrigate now also. Not something they want to do because it costs them money but they are certainly concerned about the lack of rain and its implications on tree health and production.
Hopefully we will still get lots of rain, but things don’t look promising for the near future. Unless February and March are unusually wet, it is going to end up a dry winter.
What kind of irrigation? The approach should be to refill the water in the root zone of the tree. That means a long, soaking irrigation which refills the root zone is probably best. A good soaking now and then shut the water off again would work. If we don’t get any serious rain soon and the soil profile isn’t refilled (soil moisture monitoring – soil sampling or one of the many devices available – really helps there) , then more irrigation later would be warranted.”
So hopefully, you have now read this post and the storm has produced significant rain and irrigating your trees is not necessary. However, if we have received less than a couple of inches of rain, I would suggest one irrigation for peace of mind.