Monday, May 1, 2017

Watering Trees

The west has always been my home with its dry air and endless sunshine.  I grew up in Southern Nevada and now reside in Southern Utah.  The move from Nevada to Utah with it's four seasons and green landscape was so exciting.  Of course if you are from the West Coast or back East even Utah will seem like a desert and Nevada like land desolation.  

We once took a  family trip up the Oregon and California coast visiting the Giant Redwoods and Sequoias.  I remember the the beautiful deciduous trees so thick and tall lining the roads. Truly gorgeous and inspiring! It made our Utah trees look like tiny shrubs which is why we are so grateful for whatever trees we have and are so disappointed when we lose one.  

Our 5 acres has juniper, gambrel oak groves, and pines.  Deciduous trees need water and care to survive here.  Trees and the shade they provide are such a blessing. Summer shade, fall color, wind protection, and beauty are all reasons to plant trees. Older trees are part of the history and heritage of an area.

Trees are an investment in time and money. And in the West watering is always an issue.
How often should I water landscape trees?  How do I know if my trees are getting enough water?  When do I stop watering for winter? 

Why Trees Need Water

Water is needed by plants to take up nutrients, produce food, and create a healthy soil food web.  Making sure you are not over watering or under watering can be a challenge.  Plants can suffer with over watering as well as under watering.  

A globe willow planted in the turf, not a great idea.  Notice the woody roots visible at the base of trunk.

Warning Signs of Problems


  • Soil is dry.
  • Older leaves turn yellow or brown and may even drop off.
  • Leaves are wilted and/or curled.

  • Soil is constantly damp.
  • Young leaves become light green or yellow.
  • Young shoots are wilted.
  • Leaves are green yet brittle.
  • Algae and mushrooms are growing.
  • (Univeristy of Arizona)
My son in Maryland.  Notice the tree roots over the railroad track.

What Roots Need

The soil around the roots of your shrubs and trees is called the root zone.  It is from this area that the tree needs to uptake both nutrients and moisture. Tree roots need oxygen as well as nutrients and water.  The oxygen is found in the pore space of the soil.  This is why compacted soil is bad for any plant. Walking on moist soil compacts the soil.  Paving or driving over root zones compacts the soil.  Trees that do get oxygen to the roots decline slowly and will eventually die.   Over watering and standing water can fill up pore space and suffocate roots.  Pooling water on frozen ground is not a concern because it is pooling  on the surface.

Planting in a predominately clay soil is not wise.  Clay soils do not have sufficient pore space and are easily compacted.

The importance of the site, soil type, and watering are what make a healthy tree.  Too often when a tree dies we look for disease or pest when the fact is our poor management leads to a slow decline and makes the tree vulnerable to disease and pest.  Pest and disease are usually a secondary cause of death.

A maple with it's fall colors on.

The Drip Zone

Think of the canopy of the tree as an umbrella.  Rain water tends to drip off the canopy like an umbrella.  It is from the drip line and out away from the trunk that the feeder roots take up moisture.  Feeder roots can extend from 1-4 feet past the drip line.  Watering close to the trunk does not benefit the tree because the tree does not have feeder roots in that area.  Typically, there is more root growth out from the tree than straight down.  

Feeder roots are connected to the trees by larger transport roots, trunk, branches, and twigs. Feeder roots are non woody roots that fan out near the surface.  Their tips absorb water and nutrients.  It is the feeder roots that are damaged and killed by fluctuating water levels and temperature.

Roots do not grow toward anything in particular but grow where they can be sustained by sufficient pore space, nutrients, and moisture.  They will not extend into compacted soil with no pore space for oxygen or water.  The action of microbes and the soil food web help to provide a loose nutrient rich soil with pore space for tree roots to easily penetrate

There is no such thing as shallow rooted or deep rooted trees.  While there are typical root systems for different tree species, the root system of the trees will depend on the soil type, availability of oxygen, nutrients, and moisture.  So your cultural practices and placement of trees will to a large extent determine the health of your trees.

Native trees have developed interesting adaptations to their environment. Interestingly pines in desert sands tend to grow two layers of roots.  A surface layer to absorb moisture and and a deeper layer to survive during drought. That's a topic for another post.

My favorite tree showing off its fall colors.

How deeply do I need to water?

The majority of the trees roots are in the top 2-3 feet of soil. With the feeder roots in the top 18-24 inches.  Most trees do not have a tap root. When first emerging a tree sends down a root but the majority of roots radiate out from the trunk horizontally forming framework roots. Feeder root fan out near the surface from the woody framework roots.    Think of the roots spreading out from the tree like a pancake not extending down like a carrot.  Roots can spread out from the trunk twice the length of the the branches. It is from the drip out that watering is most beneficial not around the trunk.

Remember that while there are roots that anchor the tree, your goal is to provide water to the feeder roots that fan out near the surface.

My son in  Samar, Philippines.  Anyone know what kind of tree that is?

How to determine how deep you are watering

Use a probe 1/4 inch thick to determine how deep you are watering.  After irrigating push a  metal probe into thee soil.  It will move easily through moist soil and be more difficult to move through dry soil. This only needs to be done once to help you determine how long you need to water.

  Shrubs 6-12 inches

Trees 18-24 inches

My husband by the skeleton of a juniper.  This is at a presumed UFO landing sight in Aztec, New Mexico. Make your own assumptions about how this tree was damaged.

How Frequently  do I Water?

This will depend on the season and weather conditions.  In my hot dry summers I water once a week.  In the spring and fall I water when the soil dries out down to 3-4 inches. Mature trees that receive sufficient rainfall may not need any watering.  So a lot depends on your zone and precipitation levels each season.

Summer—Generally you should water mature trees and shrubs no more than once a week. 
Water arid adapted plants less often, if at all.

Winter—If there has not been any precipitation for four to six weeks, water deciduous and evergreen trees and shrubs to keep the root zone moist if the ground is not frozen.

Evergreen trees continue to transpire through the winter.  Be sure to water well around Thanksgiving time and then in winter if there is no precipitation and ground is not frozen.

A juniper that is about 40 feet tall and native to the area.

How long should I water?

The amount of time you water will depend on your water system, the weather, and your soil type.  Sandy soil needs a shorter watering time but water applied more frequently.  A clay soil needs less water applied slowly.  Determine with a probe how long it takes to apply the water and use that as a guide.  Be sure to allow nature to do her job and adjust your watering to the weather.

My son in Biliran, Philipines.  Watering is not an issue there.

Beautiful beach in Biliran, Philippines

Additional Information

Leaving leaf liter protects roots from winter injury

Potted trees at a nursery that are not moved out of the winter weather and the summer heat suffer root damage.  Bare root trees are always healthier than container trees.

Applied herbicides on lawns where you have trees can damage surface roots and cause yellowing and damage to trees

Plastic mulches or too thick a layer of mulch can immobilize nutrients, cause fermentation, and cut off oxygen supply and kill or damage the tree.  It is best to mulch only 3-4 inches thick with a shredded bark or a natural mulch.

Expand the watering basin as plants grow

Observe your trees closely periodically.  Correcting a watering problem early can save your tree.  With older mature trees damage will occur slowly over time so look for signs of stress. 

Trees add wind protection, beauty, and cool shade to the landscape

And fall color

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