Along with assigned days, plants dictate when you should water

Q: I live in northwest Las Vegas. Our restrictions are to water three days a week in the fall, and never on Sundays. Of late, the Southern Nevada Water Authority has commented that trees, shrubs and plants are to be watered two days a week. I have a desert landscape, no grass anywhere. Is this law now, or is it just a suggestion?

A: A measure passed by the Nevada Legislature in 2021 will prohibit the use of Colorado River water delivered by water authority member agencies to irrigate “nonfunctional grass,” beginning in 2027. The law applies to Southern Nevada commercial, multifamily, government and other properties. It does not apply to grass in front and back yards in single-family residences.

The water authority’s Board of Directors established a citizens’ advisory committee to help it implement the new law. Its activities include defining what constitutes “nonfunctional” grass. I believe the SNWA wants to overtake Tucson, Arizona, (average of 80 gallons per person per day) as one of the newest low-water-use communities in U.S. deserts.

The water restrictions allow you to water as much as you can afford but only on days assigned by the authority. For instance, big trees, like most mature pine trees, should be watered 3 feet from the trunk to as wide as the canopy and about 3 feet deep. Smaller trees should be watered 18 to 24 inches deep with water applied to most of the canopy.

When to water next depends on the tree and where it comes from. Desert trees allow for their soil to be dry between waterings. But trees from wetter climates can’t tolerate such dry soil. It must be nearly dry or moist when watered again.

But there’s no getting around the fact that we live in the desert. To save water, all plants should come from a dry or arid climate. If not, then the plant that needs water most often will control when to water all plants.

Q: I’m on the board of an HOA in the Las Vegas Valley. Our community has fewer than 300 homes but owns an extensive greenbelt with dozens of trees that are showing their age at 50-plus years. We are ready to embark on a program to cull the dead and dying trees, but since many of them are pines, and we really don’t want more pines, we aren’t sure about good options to replace them. We’re looking for as much shade as possible, easy maintenance without much annual pruning or other specialized upkeep, and minimal water use. Some will be for xeriscape areas, while others will be in grassy areas. Is there any advice you can provide us?

A: Get rid of any cool-season grass areas, such as fescue lawns, as soon as possible. Turf-type tall fescue needs about 8 to 9 feet of water every year. Cool-season grasses stay green all year, but you pay a price for that luxury.

Warm-season grasses are harder to find. These include Bermuda, zoysia, buffalograss, paspalums, etc. Most warm season grasses die back (because of the cold temperatures) for most of the winter. They need very little water during those months.

Don’t plant pine trees. They are big. That’s why they need extra water. Plant a low-water-use tree that is a similar height as the house.

You didn’t mention whether the homes are one story tall or two stories tall. That makes a difference. Smaller trees shade the sides of one-story homes. Two-story homes need bigger trees for shade. Size matters when it comes to desert watering.

Q: I had several queen palms put in around my pool in Las Vegas just over three years ago. They were doing pretty good for the first year and a half but were significantly declining during the last year. They are fertilized once a month between May through September. I also applied extra manganese sulfate to help with the frizzle top. I had one water head on each palm, but in the spring I changed it to four lines on each tree, 10-13 inches away from the trunk. Drip heads installed are 2 gallon per hour, and I was watering five days in the summer, 20 minutes in the morning and 20 in the evening. Now I’m down to three days a week for 20 minutes in the morning. One of the palms lost all leaves. When I pulled it out and cut the trunk at the bottom about 2 feet up, it was pretty soft and mushy.

A: I believe you are watering too often. Give it more water but less often. Let the soil drain. They should be given water like your other trees and large shrubs — three times a week in the summer. No more than that. They will like 2 to 3 inches of wood chip mulch applied to the surface of the soil.

You do not need to fertilize that often. Once or twice per year is all that is necessary. Use a palm fertilizer if it contains manganese.

Q: I water my trees with drip irrigation, now twice a week, 30 minutes each time. The first time is 7:30 a.m. and the second is 9:30 a.m., and that is it. The shrubs and plants get water for 15 minutes twice a week, again at 7:30 and 9:30 a.m. I also adjust the clock controller times according to the season: earlier in the summer to decrease evaporation and later in winter, spring and fall when it is not so darn hot. I have had no plantings die or turn brown, and all seem to be doing well. But do I need to adjust the amounts of water and times of irrigation?

A: To be accurate, I would need to know the amount of gallons, not the number of minutes. As I tell my readers, “I can drink a lot of coffee in 30 minutes!”

Another way to look at it is in total landscape water use. Pick one of the hottest summer months. One acre is 43,560 square feet. Find out how much landscaped area you are watering. Is it a quarter acre (10,890 square feet)? One-eighth of an acre (5,445 square feet)? One-tenth of an acre (4,356 square feet)?

Bob Morris is a horticulture expert and professor emeritus of UNLV. Visit his blog at xtremehorticulture.blogspot.com. Send questions to Extremehort@aol.com.