Know Your Roots - Trees, Roots, and Water

Trees, Roots, and Water

Have you ever tried to dig a hole in an un-watered part of your yard in the middle of summer?  It’s darn near impossible, isn’t it?  People think their tree can survive in ground like that.  No way!

In the Grand Valley, trees need us to provide them with additional water to supplement the amount that falls from the sky.

Let’s be clear.  Trees, for the most part, do not have taproots that extend down to the water table.  Tree roots exist substantially in the top 18 inches of the soil, and this is where they need to find water. 

In exchange for us providing a little care and attention, our trees will provide us with shade, oxygen, twenty-degree cooler pavements and an improved environment, while removing carbon from the atmosphere.  

Look at the picture below, which represents a mature, fully established tree; it will help to explain what we are talking about as you read on.

How often to water: 

Newly planted trees (or shrubs) require more frequent watering than established trees and shrubs. They should be watered at planting time and at these intervals:

For 1-2 weeks after planting check daily, water as needed to maintain moisture in both the rootball and the backfill.

• For 3-12 weeks after planting, water every 2 to 3 days.
• After 12 weeks, water weekly until roots are established.

 Note that watering should provide good soil moisture but not completely saturate the root zone.  Excessive watering can be as damaging as no water.  Roots need oxygen!

In the Grand Valley, an established tree can be watered every two to four weeks, but needs deep watering, to a depth of about 18 inches.

Take note that a smaller tree will develop a complete root system much more quickly than a large tree.  For instance, under ideal circumstances, a 1-inch diameter tree may fully establish in two years, while a 3-inch caliper tree will likely take five years or more. 

For a newly planted tree, water should be applied directly to both the root ball and the surrounding backfill.  Drip emitters and micro sprayers work well for this situation.  if you do not have a sprinkler system, let a hose trickle slowly onto the root ball or use a watering bag like the one shown here.  A low-cost solution is several plastic buckets with two or three small holes drilled in the bottom.  Not an attractive solution but gets the job done in a pinch!

How to Water: 

A tree that has been in the ground for a while but is not fully established (new growth is less than 4-6 inches in length) should be watered from the edge of the root ball out to the drip line and possibly a little beyond.   In this picture, a soaker hose or emitter tubing laid out in a spiral is connected to a garden hose.  As the tree grows outward additional tubing can be added to increase the watering diameter.   Note that this setup may need to run for several hours to water to the needed depth.

 This picture shows a fully established tree.   Note the extent of its root system, traveling far beyond the tree’s canopy.  As this tree is planted in an irrigated lawn area, feeder roots grow upwards and coexist with the lawn’s root system.  The turf is most likely watered by spray heads, impact or rotary sprinklers.   Watering less frequently and more deeply will encourage a stronger and more healthy root system for both lawn and tree.

 Sprinkler Types and Watering Efficiently: 

This is the common pop-up spray head, made by all manufacturers.  This can be used on domestic or raw water systems (with 30-mesh) filtration.   Besides being the most common sprinkler, it is also the most wasteful. A full circle spray head may deliver 4 gallons per minute, which is about four times the speed at which water will infiltrate into the ground.  Where does the rest go?   This issue can be fixed by replacing the spray nozzle with a rotary type of nozzle, seen on the right.  

The impact sprinkler shown below is very common in the Grand Valley because it works well with our silty irrigation water.    The standard nozzle delivers 3 gallons per minute, with interchangeable nozzles ranging from 1.5 to 6 gallons per minute.  Although these are relatively easy to adjust, they are commonly used out of adjustment and with incorrect nozzles, leading to a great deal of wasted water.  It is not the best choice for domestic water systems. Gear drive rotary sprinklers are also used to water larger turf areas like parks and golf courses, and some are designed for use with filtered irrigation water.

The spike bubblers and sprayers are popular because they can be used with both domestic and filtered irrigation water, and since they connect to 1/4 inch drip tubing they are easy to install.  The knob on top can be rotated to increase or decrease the flow or shut them off completely.  These are not true drip irrigation, with flow rates up to about 20 gallons per hour, but they are well suited to watering individual young trees, shrubs, and flower beds.

The emitters below are for true low-volume drip irrigation, typically used with domestic water with a filter of 120 mesh or finer.  The ones shown are color coded for flow rate, with blue at 0.5 gallons per hour, black at 1.0 gallon per hour, and red at 2.0 gallons per hour.  These are highly efficient ways to deliver water to a specific spot.  Keep in mind that because the flow rate is so slow, a sprinkler system zone using these will need to run for a longer time.  These can work well for a newly planted tree.

Emitter tubing like this has emitters built into the tubing at spacing of 6 inches, 12 inches or two feet. Each emitter typically delivers about a half-gallon per hour.  This tubing can be installed in a grid pattern in a flower bed or even under a lawn, or in concentric circles around a tree.  As a tree matures additional coils of tubing can be added to expand the watering area.

Note:  The flow from traditional sprinklers is measured in gallons per minute, whereas gallons per hour is used for drip irrigation and micro sprayers.   Watering everything for 10 or twenty minutes a day regardless of the type of irrigation is a formula for disaster.  Do the math on watering schedules and you will have healthier plants and likely save wate