Watering Trees Efficiently and Effectively: Trees and Water are Both Invaluable Resources
Fact: Trees are living organisms that require water for survival, with most trees requiring 25-35” water a year to maintain health. All trees need regular, deep watering when soil moisture is low.
Fact: Missoula has a semi-arid climate and receives only 14” precipitation a year.
Conclusion: Missoula’s trees need supplemental water, especially during the hottest and driest months of July, August and September.
Water Where it counts
Newly Planted Trees: The best way to focus water on a young tree’s root ball is to form a small temporary earthen berm/watering well around the tree, about 3’- 4’ diameter and about 4”- 6” inches high. Fill it slowly by placing a garden hose set at a slow flow near the base of the trunk, and then let it drain.
For the next 2-3 years, the berm should be expanded to encourage the roots to grow out and away from the trunk and then removed altogether.
Irrigation bags are also effective in watering newly-planted trees, but only for the first 2-3 years after planting. The roots must be encouraged to grow out and away from the trunk.
Maturing Trees: As a tree grows, the area that needs to be watered around the tree also expands. Be sure to concentrate the watering a few inches out from the trunk to one foot beyond the edge of the farthest-reaching branches (the drip line).
Mature Trees: For mature trees, water about 9” from the trunk to a few feet beyond the edge of the farthest branches (the drip line), where the majority of the feeder roots are.
A mature tree’s roots grow 12-18” deep and extend 2-3 times the size of the canopy (shaded area).
HOW MUCH water? Just enough.
Not to be cheeky, but it’s a very difficult question to answer.
Watering depends on the specific tree and how long it’s been in the ground. It also depends on the type of soil and how well it drains. Not enough water is harmful for the tree, but too much water is bad as well.
With that in mind, here are some general watering guidelines:
Check the moisture of the soil BEFORE watering. Since every soil’s composition and drainage can be different (even on the same property), it is important to check the soil before watering. To determine whether or not your tree needs water, use a spade to open the ground at least four inches deep and check for moisture with your hand. Remember, the surface will dry out much faster. If the soil below ground is still very wet to the touch, water less. If it is dry to the touch, it is time to water.
Over time, you will become familiar with how much water each of your trees needs during mild and hot weather.
Newly planted trees Using a 5 gallon bucket poured very slowly around the planting hole, be sure to thoroughly water trees immediately after planting to ensure any remaining air pockets have been removed and that the roots do not dry out.
Trees - the first two years A newly planted tree needs much more water than one planted six years ago. New trees require about 5 - 10 gallons a week during mild weather and up to 15 gallons a week during the hot, dry summer months of July, August and September. During the first couple growing seasons, your newly planted tree is expending a lot of energy trying to get its roots established in the soil. Especially during the first few summers of your new tree’s life, it will have a difficult time dealing with heat and drought. Deep watering can help speed the root establishment.
Maturing trees Increase the amount of water to soak the expanding root area to a depth of at least 8”, and as the tree’s canopy grows out, extend the watering area to cover the entire drip zone.
Mature trees Mature trees vary widely in their need for water, depending on size, age, species, soil types and slope. That’s why it’s important to check the soil’s moisture at least 4” down once a week. If it’s moist, no need to water. If it’s dry, it’s time to water. Generally, mature trees need 2” or more water a week. A mature tree’s root system is roughly 18” deep, so allow the water to penetrate the soil until it is saturated to a depth of 16-18”. Be aware. Mature trees require more water when growing near heat traps such as driveways, sidewalks and streets.
Over-watering is a common tree care mistake. Please note that moist is different than soggy, and you can judge this by feel. A damp soil that dries for a short period will allow adequate oxygen to permeate the soil. Trees do not grow or fair well in soil that is constantly wet — it is best to let the ground dry out between watering.
WHEN should trees be watered? When the sky isn’t providing it.
Again. Not an easy question to answer.
Missoula experiences its hottest and driest weather during the summer months of July, August and September. However, June and October have been known to be as equally hot and dry, so as a rule, if there has been no precipitation for one week, your newly planted trees will need watering. If there has been no precipitation for a month, begin watering your mature trees.
HOW OFTEN should trees be watered?
Again. It depends.
It depends on your soil content. The more clay in your soil, the longer it will hold on to water. The more sand in your soil, the quicker it will drain and dry out. Soil content can even vary within a single property. It also depends on the trees. Some trees require more water than others. Some trees absorb water more quickly than others.
This is why it’s important to test the soil around each tree for moisture before watering, to become familiar with each tree’s water needs.
Start with watering the mature trees once a week. Add another watering day if the soil is completely dry when tested by touch or if it becomes much hotter and windy. Newly planted and maturing trees will require more frequent watering.
The Time of Day Matters Water early in the morning or after the sun has set; as this is when trees replace the water they’ve lost during the day. Also less water is lost to evaporation at these times. Mulching your tree will also keep soils warmer in winter & cooler in summer.
Tree Watering Methods
The best way to water trees is slowly for a long time, so the roots have time to absorb the moisture from the soil as it soaks down. The roots that absorb the water aren’t deep. They spread out sideways and most are just a foot or so beneath the surface of the soil. On a mature tree, roots extend far in all directions, but it’s sufficient to concentrate on watering the area beneath the branches.
Newly planted trees and young trees haven’t yet grown a large network of roots. That’s why they can’t store much water and need to be watered often. They should be watered near the trunk, where the root ball is.
You can water several ways:
Whenever watering a tree with an open hose, it should be flowing at a very slow dribble, so that the ground has time to absorb the water.
Place the hose on the ground near the trunk. After half an hour, move it a couple of feet around the trunk. Keep moving the hose from place to place until it has dribbled for an hour or even two hours for a large tree.
The larger the tree, the more time it will take to water deeply and to make sure the area from just outside the trunk to a foot or more outside the canopy drip line is covered.
An unattended open hose is often a forgotten hose; a lot of water can be wasted.
Soaker hoses are a very efficient way to water trees without wasting water. There is no runoff compared to sprinklers, and less water is lost through evaporation. Soaker hoses ensure that water is not wasted by helping deliver a steady, slow release of water right at the soil line.
Water slowly seeps out through tiny pores along the length of the rubber hose at a flow rate the ground can absorb. The water goes right to the root zone with very low water pressure allowing roots to gradually absorb the water.
Lay the soaker hose in a spiral pattern to cover the tree’s drip zone. If the area is too large or there is not enough hose, start with the soaker hose circling closer to the trunk and then periodically pull the hose further away from the trunk in concentric circles to ensure the entire area receives water.
If buried under mulch soaker hoses should last several seasons.
For more information about soaker hoses, click here.
When using a sprinkler, turn it down low to keep water from splashing up on the leaves, to limit the amount of water lost to evaporation and to limit the amount of water lost to runoff. The tree needs the water in the soil, where its roots are.
If using a sprinkler to water the lawn around a tree, do not assume the tree’s roots are also getting the deep watering they need.
If a tree is too far for a hose, use a bucket. Slowly pour the water close to the ground, all around the trunk and within the tree’s drip zone.
For a young tree, try to deliver at least 10 gallons every time you water.
Let’s Talk Mulch
Bare soil really doesn’t make any sense. A four inch layer of mulch, kept a few inches away from the trunk, covering the soil will slow the water’s evaporation, keep the weeds down, prevent a hard crust from forming on the soil surface, cool the root zone and create a healthier environment for the beneficial microorganisms in the soil.
Tree Watering Facts and FAQ’s
Do drought-resistant trees need water?
Drought-resistant trees need water to thrive and survive. Even though they are able to withstand periods of drought, it is not ideal. And every tree, drought-resistant or not, needs consistent water during its first few years to get established.
Do native trees need water?
Native trees will thrive better and have a better chance of survival with consistent watering; however they usually require less water.
What does “Deep Watering” mean?
Deep watering consists of keeping the soil moist to a depth that includes all the roots.
If I water my lawn, am I also watering my trees?
Maybe. Grass roots grow 4-6” into the soil and will compete for water with tree roots. When watering the lawn, make sure it is enough time for the water to reach beyond the grass roots and to the tree’s roots.
How do I know if I’m watering 1” or 1’ of water?
It depends on your watering method.
Hose: Turn your hose on a very low dribble and time how long it takes to fill a 5-gallon bucket. Time how long it takes to fill.
Soaker Hose 5/8”:
200 minutes delivers 1 inch of water
150 minutes delivers 3/4 inch of water
100 minutes delivers 1/2 inch of water
50 minutes delivers 1/4 inch of water
Sprinkler: Turn the sprinkler on low. Place a container under a sprinkler’s water spray. Check the container after an hour to see how much water has been delivered. This will tell you how much water reaches the ground from your sprinkler.
Bucket: Depending on the size of the bucket, you know exactly how much water you are delivering to the tree’s roots as long as you pour it slowly around the perimeter.