Irrigation Frequency of New Desert Ironwood Trees

Q. I have two desert ironwood trees that are ten years old, 12 to 16 feet tall, in my landscape. A nursery told me I should water these trees deep daily for 7 to 10 days. I did that and after the third day the leaves turned a pale yellow and fell off to the touch, so I have stopped watering. The soil moisture meter I use is showing 7 to 8. Any thoughts because I really don’t want to hurt these beautiful trees.

A. When you call these trees “desert ironwood” I am guessing you mean the ironwood native to the Sonoran Desert. It’s a beautiful native desert tree that does not need to be watered very often. It is considered an indicator tree for growing citrus so during cold weather in southern Nevada it might get damaged. There are other trees called ironwood as well.

            Because it grows in the desert, it is not used to getting water very often. When you water this tree, irrigate the area under its canopy to a depth in the soil about 18 to 24 inches. Then don’t water again until the soil dries out. Because it’s a desert tree, it will not like wet soil but soil that occasionally gets wet. That’s why the leaves are yellowing and falling off; watering is too often and the roots are suffocating.

            On the soil moisture sensor, or meter that you have, the needle should be in the three or four spot before you water again. The meter reads zero to ten with ten being sopping wet. You want the soil to be on the dry side about six inches deep, not the wet side when you water it again.

            When you do water, try a hose, an inexpensive sprinkler that screws onto the end of the hose and a mechanical timer that shuts off the water. If you are like me, I forget to turn it off. The mechanical timer will shut it off for me. Set it for one hour. Take a length of rebar and stick it into the ground in three places and make sure the water got to the right depth. If the water isn’t deep enough then water for 15 minutes more.