Sago palms turning yellow? Here’s why

Q: The sago palms (cycads) in my yard are turning yellow. Can you tell me what they need?

A: There are three reasons why they are yellowing: their location (landscape exposure), needed soil amendments (including fertilizers) and improper watering. It is up to you to figure out which one (or several at the same time) might be responsible.

Judging from the pushing of new growth from the plants’ center, I think they are getting enough water during the week. Water this plant three times a week, not more often than that. Don’t reduce the weekly amount of water it is getting but apply it all at once.

When you are watering, apply it to a depth of 12 to 18 inches. This will mean that you need to apply in a single application anywhere from 5 to 8 gallons of water. Apply this water through three emitters, located 12 inches from its trunk, to get a good distribution of water.

Don’t split the application of water in the morning and another in the afternoon. That’s silly unless you see an enormous puddle of water when you irrigate. If water puddles on the soil surface, split the application of water into two applications an hour or less apart.

This plant is originally from the richer soils of northern India. It evolved with these types of soils. It doesn’t like the extremely low organics of desert soils.

Iron fertilizers should be added to the soil in the early spring but now is OK to do it. Be sure to add this composted soil where the soil gets wet.

If the compost you are adding comes in a bag without a description, then it is probably low in fertilizers as well. Mix in the appropriate fertilizers to the compost before mixing it with the soil.

Make sure any surface mulch is at least 2 inches deep. Using mulch adds one or two days of extra water. Mulch can be crushed rock or wood chips. Wood chips are better because they decompose in wet soil adding organics to it as the wood chips decompose.

Crushed rock doesn’t add any organics back to the soil. You should add organics to the soil (compost) every two years if the mulch is crushed rock.

If a lawn was removed in the past three to five years this might explain the yellowing as the lawn adds organics back to the soil. Removing the lawn also removes the organics.

I don’t think this cycad will be better in a different location, but cycads grow best on the north and east sides of a home. They prefer to grow with morning sun and afternoon shade.

Q: My agave is 10 years old and just isn’t looking healthy. I’m afraid of losing it and the surrounding plants. I can’t figure out if it’s too much or too little water. Your expertise would be appreciated.

A: Most problems with agaves are from boring into the trunk and roots by the agave weevil and little to do with water. Eventually the immature forms of this insect tunnel into the base and trunk of susceptible plants.

All agaves should have a systemic insecticide applied by spray or soil drench in the spring, no later than March or early April. With spray insecticides, it’s important to spray the lower leaves and the surrounding soil at this time. With soil drench insecticides it’s important to apply it to the soil immediately around the plant at the appropriate time.

American agave, in particular, is very susceptible to this pest. Be sure the appropriate insecticide is used by reading the label.

The agave weevil lays its eggs in susceptible agaves and some yucca when temperatures begin warming in the spring. These eggs are laid by the agave weevil inside the lower leaves, close to the trunk, around that time. A single application of a systemic insecticide is needed around that time. I don’t know of any proven organic methods to control this insect.

If you are still concerned about watering and drainage, make sure that these plants are not watered daily. All perennial plants need the soil to drain away from their roots. Some plants like agave and cactuses should never be planted at the bottom of a ridge. Too much water accumulates in those spots for agave. Other plants may need a supply of constant water but not most agaves.

Q: We have multiple red yuccas in our front yard. For the first time, they have started turning yellow in the last few weeks. They are on a drip irrigation system and are watered twice daily for five minutes each time in the early morning and late evening. Any idea what the issue could be?

A: They are watered too often. Red yucca (Hesperaloe parviflora) is native to the desert Southwest. They can be found growing naturally in the Chihuahuan desert of western Texas, New Mexico and in the state of Chihuahua, Mexico.

They don’t need water frequently but they could sure could use applications of water 12 to 18 inches deep when they do get it. Slow, deep applications of water are ideal for drip irrigation.

Applying water every three weeks or so will get them to grow larger. Applying water every eight weeks, but still deep, will sustain their size.

Watering frequency causes desert plants to grow. Irrigating them three weeks apart will get them to grow larger while watering them with the same amount of water less often than three weeks apart, perhaps eight, will sustain their size.

Experiment with your soil. They can be watered slowly with a garden hose or connected to the irrigation system with an irrigation clock, but using the timer only when the plant needs water.

Q: I have ground squirrels that are killing my agave. They dig around it, eating the roots and finally killing it. What do I do? How should I protect it?

A: The ground squirrel you’re seeing is referred to as an antelope ground squirrel. They are omnivorous which means they will eat insect grubs if they find them. But when food is scarce, my feeling is they will go after anything.

I think what you’re seeing is an attack first by the agave weevil in the spring with the ground squirrels digging up the grubs and eating them. In any regard, it’s always best to drench the soil around these agave weevils with an insecticide when spring temperatures begin to warm up.

In our climate, it is normally the end of March or the first part of April. This application protects all agave. If you have agave and want to keep them, you must protect them from agave weevil in the spring. I don’t know of any organic methods that have been tested that I can recommend.

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.