How can I stop my palm trees from turning yellow?

Q: My cycad (sago palm) is yellow. I had read that it needs magnesium. What do you recommend?

A: Make sure the soil in your container drains and the plant is not watered too often. Repot or replant the sago palm when temperatures are cooler. Either wait or take it inside your house where it’s cooler when you replant, and the plant reacclimates to the repotting in a week or so.

Use a soil moisture meter when watering to make sure it’s not watered too often. Sometimes watering too often and poor container drainage of the soil can cause plant yellowing.

Judging from your picture, your plant yellowing may be a fertilizer (plant nutrient) or a watering and drainage problem. Iron shortages in plants are notorious for yellow foliage.

Try applying an iron chelate to the soil when growth is first starting. Applying iron to the soil works if the plant is still growing. Once the plant stops growing, then iron applications to the soil don’t work very well.

After around June or early July, iron applications must be sprayed on the new leaves and stems. In some cases, multiple spray applications a week apart are needed during that time.

Before new growth starts in early spring, apply this same iron chelate mixed into the soil. It’s much easier. If in doubt, use an iron chelate containing EDDHA. Search for it online if you can’t find it.

Magnesium deficiency is usually a speckling of leaves or fronds. It’s not usually yellowing.

Epsom salts contain magnesium, so apply 1 to 2 tablespoons to the potting soil. It won’t hurt the plant. After replanting, water the plant until water comes out of the bottom of the container.

Though sago palm or cycad is not a palm, lightly apply palm fertilizer to the soil once a year in the early spring.

Q: I have read that plants grow better when water is delivered to their roots at the same spot over and over again. Is this true?

A: Yes, it’s true, but you probably won’t notice the difference. Plant roots get used to the amount of water and air when water is delivered to the same spots and depth, over and over.

That is one reason why drip irrigation, with the proper spacing of emitters, is so successful if the plant wets its roots to the appropriate depth each time. Watering with a hose will not be as consistent.

Water should wet the roots to the same depth every time. Small shrubs need to wet their roots to a depth of 12 to 18 inches, medium-sized trees and shrubs 18 to 24 inches deep, and tall trees or shrubs should have wetted roots to a depth of 36 inches deep.

This water should be applied to at least half the area under the plant’s canopy. Obviously, large plants need more water applied to them, and this water is applied to a larger area, than the smaller plants.

Q: When installing drip irrigation, what irrigation parts do I need?

A: Make sure there is some sort of filtration, a pressure regulator to lower water pressure, and a way to flush the irrigation lines of debris, algae and bacteria. Many people forget the flush part because they are used to using city water.

Every drip irrigation system needs these parts. It makes no difference if the filter or pressure regulator is first. It works either way, but the arrows of water flow are important.

The flush valve — oftentimes just a ball valve — is placed farthest away from where water first enters the system and is hidden from site but easily found and used. The flushing operation involves cleaning the filters and cleaning the lines of algae and bacteria with the flush valve.

Lower the water pressure with a pressure regulator. Water pressure from a municipality fluctuates depending on how close you are to the municipalities water pump or reservoir. A plastic pressure regulator helps lower the water pressure into the normal range to operate drip irrigation.

The pressure of water from wells may vary. For most homeowners, the water pressure range for smaller drip systems is approximately 25 to 30 psi. For larger drip irrigation operations — half acre and above — water pressure of drip systems may need to be more than this.

Water used in drip irrigation needs to be particle free. Drip irrigation relies on small holes that can plug, to deliver water. Clean water requires filtration.

Though water from municipalities has been filtered, filtration is still needed for drip irrigation. Most common and inexpensive screen filters (screens are 120-130 mesh, which means 120 to 130 holes per each square inch) are used. The filter is added, usually after an irrigation valve.

Regular flushing cleans the lines of debris, algae and bacteria. It is important to flush the lines every time repairs are made as well as regularly.

Part of the flushing operation requires a separate flush valve. That is particularly true if using a fertilizer injector.

When designing drip irrigation, I prefer closed-loop systems. Closed loops minimize the places where you have to flush and even out the water pressure of the closed loop system.

Q: I received the Wittwer vegetable bible, but I must admit I’m a little confused by the title, as it seems to be pertaining to Moapa and Virgin valleys and not the Las Vegas Valley. Don’t those valleys have a different climate than the Las Vegas Valley?

A: Yes, they do. It is slightly different, a bit warmer to be exact. The climates between the two valleys are very similar. Both valleys are in the eastern Mojave Desert. It’s hard to find information from a source such as Dr. Sylvan Wittwer for the Las Vegas Valley.

Dr. Wittwer was the retired vegetable specialist from Michigan State University when he moved to our Mojave Desert climate. He grew vegetables in this climate for eight years before he moved to Utah. It’s difficult to find reliable information in the Las Vegas Valley from such a notable source.

Q: It looks like these trees have elm leaf beetle or leaf miner damage. What to do? Let the tree flush a new set of leaves after the larval feeding frenzy? These are trees cared for by volunteers and found in Spring Mountain Ranch State Park near Blue Diamond. I would rather have the volunteers not use any systemics. Any thoughts?

A: That’s elm leaf beetle damage on Siberian elm leaves. We used to see a lot of it when there were more Siberian elms in our community.

If you can catch them in the larval stage, they are easy to control by spraying the leaves with any type of insecticide. Any insecticide works including soap and water and salt sprays. You just need to kill them.

The problem is the act of spraying means specialized equipment because the trees can grow more than 40 feet tall. Soap and water sprays kill on contact. They don’t have any residual, so you must spray the leaves until the level of control you want is achieved. Otherwise, you must use a systemic insecticide as a soil drench or have it absorbed through the tree trunk.

I just ignore them and tell people not to plant Siberian elm when I see it. Recovery of this tree from single feeding by elm leaf beetles is not a problem. I have only seen elm leaf beetles eat the surface of Siberian elm leaves, not any of the Chinese elm types including lacebark elm.

Plus, the elm leaf beetle has only one generation each year while other insects, like the great leaf skeletonizer, are more destructive and mate multiple times each year.

I consider Siberian elm a trash tree and ranks about 2 out of 10 in desirability. Chinese elm, on the other hand, is a much better tree, and I would give it an 8 or 9 out of 10.

By the way, Siberian elm is no longer sold as a landscape tree. No great loss.

Bob Morris is a horticulture expert and professor emeritus of the University of Nevada, Las Vegas. Visit his blog at xtremehorticulture.blogspot.com. Send questions to Extremehort@aol.com.