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The Easy Guide to Watering Trees

Post Date:11/06/2018 3:46 PM

Easy Guide to Watering Trees - Water Blog

As humans, it’s tough to know how much water our trees need, especially when it’s really hot. Most of us assume trees need constant refreshment, like we do, and so we water them several times a week. While this assumption is appropriate in many parts of the country, our local soils change the playing field - literally!

Soil absorbs and holds water like a sponge. Tree roots absorb this water held within the soil. The amount of water this “soil sponge” can hold varies by soil type, so it is a crucial factor to consider when watering trees. Our local clay soils can absorb a lot of water, albeit slowly, and hold it for a long time. This means that, once the soil around a tree’s roots is wet, there is a lot of water available for the tree for a long period of time. It is because of these soil characteristics that trees in our region prefer deep but infrequent watering.

Now that we understand our local watering principles, it’s time to figure out how to actually water our own trees. Fortunately, scientists have already done most of this work for us! Below are 4 easy steps to get you started on your custom watering schedule.

Step 1: Estimate tree water needs. Scientists have correlated the gallons of water a tree needs with the diameter of the tree canopy (i.e. the distance across the leafy crown). Using the table below, find the canopy diameter of your trees and the correlating gallons of water you should give your trees every time you water.

Tree Canopy Diameter










Gallons Needed Per Watering










Step 2: Estimate drip system flow rate.
Now that you know how much water your trees need, it is time to figure out how fast your drip system delivers water. Below are several ways to determine the flow rate of your drip emitters, the small devices that release water to your trees from the mainline tubing, in gallons per hour (gph):

  1. Estimate: Take a look at the flow of water from the emitter and, using the attached graphic, estimate the flow rate.
  2. Inspect: Many emitters have the flow rate stamped somewhere on their surface or labeled on the packaging.

Step 3: Calculate run time. You now have the information you need to figure out how long you need to run your drip system: simply divide your gallons needed by the gallons per hour delivered and – voila’ – you have calculated your run time! Easy peasy…for the most part. Since most of us have more than one tree and a varying number of emitters on each tree, you may have to do a little extra math. Also, keep in mind that 4-8 hour run times are not uncommon.

  • If your tree has multiple emitters, add all the flow rates together to calculate the total flow rate. Then divide the gallons needed by the total flow rate to calculate run time.
  • If you have different size trees that require different run times, start with the average run time and adjust as needed.

Step 4: Adjust watering schedule. Now that you know how long to run your drip system, it’s time to determine how often you need to water. Just like people, your trees will use less water in cooler temperatures and more when it’s hotter. So, in order to give your tree the right amount of water throughout the year, it is important to adjust your schedule at least every season. Using the table below, determine how often you should water.

Days Between Watering







Desert Adapted





High Water Use






If you are used to watering several times a week, shifting to once a week can be a stressful idea. But fear not, there is no rush to make big changes. You can simply extend the days between watering by one day and see how your trees do. If everything looks good after a month or two, extend it another day. Continue this routine until you feel you have reached the optimal watering schedule for your trees. Remember, irrigation is an iterative process. Use this guide to get started and then make adjustments as needed.

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