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Water Your Trees, How Much and When

by Keith Brown
May 22, 2009

You should water your trees. Watering your tree can be the best treatment for improving tree health. But, watering improperly will provide zero or negative help to your trees and waste a valuable resource. The complicated part of knowing how much to water is recognizing that different trees have different needs and different planting sites will have different drainage and water holding characteristics. This blog isn’t about learning to be a hydrologist, but here are a few general tips to point you in the right direction for properly hydrating your tree.

For starters, it is important to know that your tree needs the soil to dry out as much as it needs to be watered. There is a “breathing” process by which water pushes air out of the pore spaces when you water, and as the soil dries air is drawn back into the soil pore spaces. Roots require oxygen to grow, therefore, you need air in the soil.

If the tree is on a steep rocky slope you will need to water differently than if you are on a flat piece of land with some soil. Steep rocky slopes don’t hold water for long. This means you will need to either: water more frequently a slow drip, or run your irrigation on shorter (10 min) intervals for four or five times per watering. If you are on flat ground with some soil you can water less often, and you can crank up the water’s flow rate for a shorter amount of time. Since the water won’t be running away it will slowly seep into the soil on its own.

Newly planted trees need to be watered more often than established trees. Yes, this is totally obvious, but you should understand why. The main factor here is that this tree has recently been moved into your yard from a tree farm. Or, better described, a tree utopia, where it received regular watering, fertilizing and green house conditions. Transplanted trees will go through an establishment period where you will slowly taper down the amount of water it receives. The other reason transplanted trees need more water is because the bucket it came in did not allow for enough root growth. Until the roots grow enough to catch up in volume to the canopy it will need more water than normal.

Trees with large leaves need more water than trees with smaller leaves. You might notice that all the native drought hardy trees all have small oval leaves. The water pump system of a tree works due to the water evaporating out of the leaves causing water to be drawn in by the roots. The larger the surface of the leaf, the more the sun is cooking water out of it.

Every tree will have its own unique needs based on what species it is, its site characteristics and it’s size. To really do a good job you’ll need to get to know your trees and learn to recognize the signs of water stress. Most of the time you shouldn’t need to water more than once every three days. And, always, always, always let the soil dry between watering.

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  • Johnny says:

    Thanks for the tip! I had heard that Agaves and cactus soil should be dried between waterings, but I didn’t know that trees needed the same treatment. I just planted a 7′ tall Pecan tree in my front yard and had been watering it 2X a day for the last 2 weeks. How can I tell that the root structure is now established? Or is there a certain amount of time that I should wait after it’s been planted to start letting the soil dry out between waterings? Also, for a newly planted Pecan tree, do I wait a wait a couple years to start pruning?

    Johnny

    • Keith says:

      It is so hot out there now that I would recommend maintaining your watering schedule through the summer. The best time to plant trees is the fall. This is because most of a trees root growth takes place in the fall. It is good for tree to be growing roots as it’s first priority after being planted. This fall, after the temperatures are consistently in the lower 90′s, taper your watering regimen to a deep watering every three days. After this fall and winter your pecan tree should be fairly established. If you have a lawn that gets watered the watering for the turf should be sufficient for the pecan tree once it’s established. If not, you’ll have to play it by ear. Watch the little pecan and when it gets droopy give it a deep watering. You shouldn’t have to water more than 2 or 3 times per week.