Basin around tree trunk best way to irrigate

Q: I hand-water my trees with a hose. How often should I water my California pepper tree, Mediterranean fan palm and my Canary Island date palm with the extreme temperatures we are having? These are the only trees I have on my property.

A: We have to consider both how often and how much to water. The “how often” will be the same for these trees. In other words, they will all be watered with about the same frequency.

How much will also be about the same, except for their size. The larger the canopy or size of the tree, the more water it uses. This time of year, with temperatures in the triple digits and surface mulch around the trees, I’d water two or three times a week.

Generally speaking, a layer of mulch will save you about one day that you do not have to water. Make sure that you are leaving at least one dry day between irrigations.

I would suggest that you put a moat, depression or basin around the trees to contain the irrigation water from your hose. This depression, if it is maintained so that it stays the same capacity around the tree, will guarantee that the trees get the right amount of water each time . The depression or shallow trench can be a small when the tree is first planted but must be increased in capacity as the tree gets bigger.

The depression should be 3 to 4 inches deep and wide enough to contain 5 to 10 gallons of water when small and later expanded to contain as much as 40 gallons when larger in a few years.

The only exception to this is the palm. Many palms have the same size canopy when they are 5 feet tall as when they are 20 feet tall. So, for these types of palms, the depression can remain the same size after it establishes its full canopy.

I prefer a depression around the tree rather than a moat or doughnut. As long as the trunk dries for 24 hours after irrigation, trunk or collar rot will not be a problem. It will be a problem if wet soil is left in contact with the trunk, so don’t pile soil against the trunk that will get and stay wet.

If you leave the hose running unattended in the basin, buy an inexpensive hose water timer that you turn on like a kitchen timer. It will turn off the water depending on the number of minutes you dial in. It will save you water in the long run because, if you are like me, we tend to forget what’s cooking if we don’t use a timer.

Don’t just dig a depression and fill it with water when you are done. It will never be level unless you dig the depression at the same time you are running water. The bottom of the depression should be flat when it is finished. This type of irrigation is called basin irrigation. Fill this basin twice when you water.

Bob Morris is a horticulture expert living in Las Vegas and professor emeritus for the University of Nevada. Visit his blog at xtremehorticulture.blogspot.com.