By Nancy Penrose
A question we get asked often is, “How much should I water my trees?” The reality is this is not always an easy question to answer. It can depend on a lot of factors, such as the type of tree, the weather and general climate, soil conditions, etc. The one thing is certain, If you are planting a new tree, it will need to be watered often, if not daily.
The water a tree receives when it is young, can determine the longevity and overall health and appearance of a mature tree. Here are general points that any homeowner should be thinking of when caring for new and established trees.
How often do I need to water a new tree?
It can take 1-3 years (depending on size) for a new tree become established in its permanent environment. During this time, the tree is sending most of its energy into building new roots. This will serve not only to anchor the tree, but most importantly, take up water and nutrients. It is critical to make sure the soil does not dry out during this time. Once the tree is anchored into the ground and the roots have entered the native soil, you can start to reduce supplemental water. This critical period typically lasts about a year.
Why do I need to water a new tree even if it has been raining?
Dense tree canopies, especially that of evergreen trees, can shield the ground under the tree and block rainwater from entering the critical root area. Think of the tree acting as an umbrella over the roots of the tree. On rainy days, check the soil directly under the tree for moisture. Soil that holds shape when squeezed in the palm of your hand has adequate soil moisture. If the soil falls apart, or does not hold shape, considering giving it some supplemental water. Once the tree is established, the roots will grow past the canopy of the tree (out from under the umbrella) and will be able to access moisture in the soil better.
How much water should I give my trees?
Here is a rule of thumb you can use. New trees require 1 gallon per inch of trunk diameter the first growing season. Using this rule, a 2 inch diameter tree would require 2 gallons of water per day.
Established trees typically can go much longer without supplemental irrigation and typically a 2-3 hour slow soak with a garden hose will be enough for most species. Signs of drought stress can be early fall color, thinning canopies, and burned leaf tips. These signs could be an early indication that your tree needs a drink.
Can a tree get too much water?
Yes. Tree roots need oxygen to grow and expand. Too much water can suffocate the roots, causing root decline and dieback. Signs of overwatering can be mimic underwatering, so it can be tricky to detect. If you can squeeze water from a handful of soil, you are likely overwatering. Look for signs such as yellowing or grey foliage, mid-summer leaf drop, and a thinning canopy.
Are There Recommended Methods for Watering?
We recommend drip irrigation for most applications. Drip irrigation provides a slower supply of water which reduces runoff and allows the water to penetrate deep into the soil where the roots are.
New trees that have not yet become established, need to have irrigation focused closer to the trunk of the tree, directly over the root balls. Mature trees have roots that spread out as far as 1.5 times the height of the tree, so they need water distributed evenly under most of the canopy of the tree. Consider adding a 2 inch layer of much under the dripline of the tree. This can help retain soil moisture and also provide nutrients to the soil as it breaks down.
Do I need to water my trees in the fall and winter?
All trees enter a dormancy period (even evergreens) at which time they are not actively growing. This varies greatly from region to region, but you do not need to water your trees when they are dormant. A general rule is when fall colors start to show on deciduous trees, its time to stop watering for the season.
Nancy Penrose is the owner of Big Trees Inc., located in Snohomish, WA in the Seattle area. The company is one of the largest tree nurseries in the Seattle area with over 120,000 trees available in over 300 varieties. They not only deliver young trees, but also mature trees in a wide range of sizes. Some types of trees available include spring flowering, deciduous, evergreen, and privacy trees. The company also does tree transplanting including large trees. Their blog can be seen at https://bigtreesupply.com/blog/ or https://arboristblog.com/. They can be reached at 360-563-2700.