Desert trees anchor a xeriscape. Such important plants need proper care to look natural and avoid damage. Amazingly one of the best things you can do for a desert tree is NOT water it all the time. Over watering encourages fast, weak growth. When summer windstorms come, a spindly tree loses main branches, potentially ruining its form. My neighbor had an entire tree disappear in a windstorm!
This Mesquite is nearly full grown, yet has been severely pruned to prevent damage from wind. Watering less frequently would give a better natural form without the need for pruning.
When I plant a young desert tree, I build a basin with edges about 2 feet away from the tree’s trunk. I’ll start by watering the tree every few days for the first week or two while it recovers from transplant shock, then I fill the basin once a week while the tree gets established, about the first year. After a year, a desert tree can live with watering once every 2 to 4 weeks. If the tree seems to be growing slowly, you can increase the water frequency to no more than once per week.
A lush baby Palo Verde tree with a 2 foot basin.
As the tree grows, expand its basin. Once a year in spring you can rebuild the sides of the basin farther away from the trunk. The basin around the tree allows you to give a large drink with each watering, penetrating farther into the soil and allowing the trees roots to grow deeper. Shallow watering encourages shallow roots, which allows the top of the tree to become heavier than the root strength. In order to allow the basin to fully fill, turn a hose on at a trickle and set a timer for an hour, monitoring to make sure your basin doesn’t overflow. Or if your tree is on your irrigation system, you can add the number and flow rate of emitters needed to fill the basin in the time scheduled for your system.
A larger basin on a more mature desert tree. This basin measures about six feet across and is doughnut-shaped to encourage roots to spread away from the trunk. This tree blew over a few times while young and needed stronger roots.
Once my desert trees have doubled in size or seem well established, they can be watered even less frequently. A few of my trees border a low spot in my yard where water pools when it rains. These trees are not on my irrigation system and I hardly ever water them by hand. The winter and summer rains give them deep drinks which keep them healthy. They usually keep their leaves all season long, so I know they are getting enough water.
This Foothills Palo Verde has been in the ground about 5 years and no longer needs any irrigation since it borders a low spot in the yard.
When watered appropriately, desert trees grow slower with more proportional shape and stronger branches. Over time they can still grow to mature heights of up to 30 feet, and much more quickly than they would in the desert.