Watering Trees

​Watering the Trees


How do I know if my trees need water?


At the time of this writing, rainfall totals in the area are close to half the average. The growing season was met with no rain in May or June, a wet July and a very dry August. The perennial plants are starting to wilt in order to conserve water, but the trees have not yet shown signs of water stress. Mature broadleaf trees have the ability to transpire hundreds of gallons of water every day.    


  At what point do we need to start thinking about watering the trees in our yard? Before we answer that question there are other questions that need to be asked: 


1. How long has the tree been in the ground?  If it is newly planted this year or last         year, it will need additional water added to its roots while it is getting established.

1. How much and what quality (if any) organic matter in the form of mulch on the root zone? The wider and more diverse, the better.
   

1. Do we feel any moisture? If not, how long since we did?
   

Now, we can start to think about whether it would be wise to add more water to the results of our trees.


In general mature trees, especially those that are supported with a wide ring of mulch, will not need to be watered during the growing season.


Trees have adapted to go for a long period of time without regular watering and while it can be stressful to their systems, it is best to let them build resilience by going dry at times. Severe droughts will slow down or halt the life processes of any plant or animal and trees are no exception.


When the water in the soil has been completely exhausted, the roots can start to desiccate (die) and there will be a subsequent die back in the crown due to the lack of support system. If we have decided that the stress is great enough to intervene and add water there are more considerations and best practices. 


Long irregular waterings are preferable to small regular amounts of water on the roots.
The reason for this is that the tree roots extend out approximately 4x the diameter of the trunk or farther and reach down about 18 inches into the soil. It takes quite a bit of water over a long period of time to  soak the entire root zone of a mature tree .


If we were to water a tree every day with a little bit of water, the roots will adjust and grow in the upper inches of the soil exposing them to extremes temperature, and to desiccation if and when we stop watering. So watering your trees long, low and slow is ideal.  In fact the best time to water is right after a rainfall that has followed a drought.


If you have some trees or new plants that you think could use a drink, the perfect time to water is after or during that rain.


The quality of the water used is something that I never thought much about until recently. If you live in an area with tap water, the water is treated with chemicals and chlorine to make it “safe for drinking”. The chlorine and chemicals in the water kill organic life. The tree roots have evolved to grow in symbiotic relationship with mycorrhizal fungi, which cannot survive in chlorinated environment.


The best water to use is rainwater. If that is not available tap water can be dechlorinated if it sits in a bucket or pail for at least 24 hours.   This could be challenging for large scale watering unless you have a 250 Gallon bucket in your garage. Sunlight and the oxidation process will remove the chlorine and make it much safer for the biosphere.


Final Thought: 
Hardly any tree in an urban landscape has enough mulch from the viewpoint of “how it evolved to grow” -large, sturdy, old. If you haven't, consider putting in a mulch bed preferably of arborist chips. These will support the tree through drought and extremes in temperature. They will allow exponentially more water to get down into the soil as opposed to grass which sheds the water off like green pavement.  


More on mulch next time…


Arborist Love,


Jason LaRose