How to Water Trees and Shrubs

In order to grow well, trees and shrubs need moist but not wet soil. During the growing season you should be watering your trees once a week but be sure to check your soil before watering to make sure it is not too wet. You don’t want to over-water but do be sure to put on enough water to wet the soil to a depth of about 30 inches.

Also, be sure to wet the entire root area from the base of the tree to the ‘drip line’ at the furthest extent of the limbs. If you water too shallow, your deeper roots won’t push deep into the ground and the tree will expend energy growing roots towards the surface. A shallow root system is a sure fire way to see your tree topple in a windstorm or have the roots freeze in a hard winter.

The root zone or ‘drip zone’ is the soil surrounding the tree’s roots. This is the reservoir, so to speak, from which the tree draws moisture and nutrients. When it rains, most trees and shrubs shed rain water to the “drip line,” which is where the outermost leaves on the tree are located. Trees take in most of their water from the drip line and just beyond. They do not take in the most water from the area immediately surrounding the trunk. So, it’s at the treeline and just beyond where you should water.

How Much? How Often?

Obviously the daily weather (temperatures, precipitation and time of year) and soil quality will all have an effect on how often you water. You will want to take the time to go out and again to get an idea of the water quantity of your soil. It needs to feel somewhat like a damp sponge. If it’s wet, don’t water.

From my experience, by far the majority of newly transplanted trees die from too much watering rather than not enough. Sadly, I have a great amount of personal experience in drowning trees. But I’ve learned my lessons well. Plan on watering your baby trees with about 5 gallons every other day in dry climates and every 4-5 days in wetter areas. It takes 2-4 years for a good root system to get established (Larger transplanted trees may take a few years more to get established). During that second through forth years look at watering once a week in the summer and once a month in the winter. Try to remember that 30-inches deep guideline and adjust appropriately. By the fifth year, your tree’s root system will be well established. For mature trees, water deeply once a month during the driest part of your year.

Note that for the first few months after you plant a new tree, the tree will draw water from the root ball. The root ball can dry out rapidly so be sure to soak the soil at the base of the tree regularly for the first few months after transplanting. If you notice that your trees are showing signs of water stress don’t wait! Get water to that tree.

How?

When you think about HOW you are going to get water to your trees, think in terms of water conservation, regularity and time efficiency for YOU. By putting these thoughts together you will get a system that is best for your trees and for you.

There are several options for getting water to your trees. To begin with, you will want to construct a “well” around the base of your tree extending out several feet. This well will be a bermed feature that will hold water within the drip zone so that it soaks into the appropriate area and doesn’t just run off. Be careful in situations of heavy rainfall so that your well doesn’t collect so much water that it drowns your tree. Several years ago I had just complete planting a group of fruit trees when a tremendous downpour opened on us. After about ten minutes of pounding rain I had to run out and cut open the newly constructed well to let the excess water run out.

Of course, you can use the “open hose” method of watering your trees. The problem faced here is that you really don’t know how much water you are putting on your tree and to what depth the water is going. The other problem is that you may leave town on vacation or simply forget to water. That kind of irregularity will stress your tree. Sprinklers are another method I would caution against. While they cover a very large area, your water use becomes inefficient as it is not targeted to your trees. Wind and the sun will also take up large amounts of sprinkler water.

Options improve when you start looking at soaker hoses and drip systems. A soaker hose is a black hose made of a porous material that allows water to seep out rather evenly along the length of the hose. Place your soaker hose circled around your tree and within your well at the drip line and stake it down with two-pronged garden stakes. Again you will face the issue of not know quite how much you are putting on your trees and for how long you should do it. That said, I’ve found that newly planted trees should get about a one hour soak every other day under this method. In the second and third year you can go to a 1.5 hour a week schedule.

A timed drip system works well. Drip line is relatively inexpensive and the emitter systems are available in kits with instructions. I’ve used two 2-gallon/hour emitters for newly planted trees and shrubs and run them for slightly more than an hour every other day to get 5 gallons into the well. Again, go to once a week in your second and third year. Set your timer to water early in the morning before the sun rises. Once you have this system set up you can rest assured that your trees will get what they need while allowing you more free time and less worrying.

With all of these methods you are looking at watering the surface and thus you are not reaching the deep roots. While it is true that most a tree’s roots do sit within the first couple feet of the surface you will want to drive your roots deep to avoid that freezing mentioned above and to give the plant stability in the wind. One thing that I’ve found helpful in this sense is to vertically bury a four foot long ½-inch or even ¼-inch PVC pipe drilled with small holes just beyond the drip line. Then, target an emitter into that pipe to get the water down deep into the soil. Alternately, you can you a hose-fed root feeder or watering stake to get that water deep down in the soil.

Resources to Helpful Tree and Shrub Watering Tips

Here are some helpful tips we’ve found on the internet when it comes to watering trees and shrubs. You’ll want to keep these tips in mind, when judging how much to water. If you are looking for more information on either topic, just click the link below the quote.

Checking Soil Moisture

There is no way to look at the soil from above and tell how much moisture is in it. The only way to be sure of how much moisture is in the soil is to probe or dig. A trowel, metal rod, or soil sampling tool can be used. Low-cost soil moisture meters are not very accurate. A metal rod, such as the end of a root feeder (without the water running), may be the most convenient tool for the homeowner to obtain and use. Very dry soil will resist penetration of the rod and indicate the need for watering. After a little bit of practice, anyone can learn to use this simple tool.

Source: Watering Trees and Shrubs from The Morton Arborateum

Signs of under- and over-watering
Under-watering
- Soil is dry.
- Older leaves turn yellow or brown and may even drop off.
- Leaves are wilted and/or curled.

Over-watering
- 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.

Source: Watering Trees and Shrubs from College of Ag and Life Sciences, University of Arizona

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Jim O’Donnell gardens in the mountains of northern New Mexico. A certified permaculture designer and ecological restoration specialist, Jim’s first book Notes for the Aurora Society was published in 2009.

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