More expansive root system will help saguaro


Q: I have a saguaro cactus with three big arms growing from it leaning toward the west. On the east is my house; it shades the cactus from the morning sun. I also have been watering on the house side of the saguaro, the upslope side, and letting the water run downhill into the roots. I water about three or four times a year and water very slowly.

Do you have any suggestions about either stopping the leaning or how to straighten the cactus ? Those two large saguaros have been in my yard for 17 years.

A: These Sonoran desert monsters are top heavy. The root system of the saguaro is fairly shallow but expansive. The root system can give this top-heavy cactus quite a bit of support under native desert conditions, but they have been known to blow over in high winds.

These cactuses, like most, are opportunists and take shallow water from the soil before it evaporates or is taken by neighboring plants. Most of the roots can be found at depths less than 12 inches. Watering these plants deeply is probably a waste of water.

We put these plants in artificial desert landscapes and put them on drip emitters or run water close to the trunk. This can lead to a very small but dense root system . The roots don’t have to grow far from the trunk for water and this doesn’t help stabilize the plant as the top gets bigger.

Your cactus could be leaning because of the shade from the house or poor root support or both. If it is leaning and there is danger it will fall over, then you will have to support it.

In the meantime, create a more expansive root system by placing other desert plants close so that the irrigations from the other plants can help the saguaro extend its root system farther from the trunk.

You could sprinkle irrigate the area around the saguaro, simulating desert rainfall, but that can lead to weed invasion in the landscape .

From the pictures you sent, your watering regime obviously has given your saguaro some good growth. But, it sounds like the water is concentrated close to the trunk. I will post the pictures of your saguaro on my blog.

Another possibility that could contribute to the leaning is how it was planted. If a hole was dug just large enough for the transplanted roots and the soil was not conditioned properly, then this will encourage the plant to grow roots close to the trunk as well.

All cactuses grow better in amended soils than in straight desert soils or sand .

What can you do now? If the plant is leaning because of the house, there is not much you can do. To give it better support, put irrigation water at greater distances from the plant and use shallower irrigations.

As I said, giving saguaro deep watering is not going to help, but getting its roots to grow wider might. If the soil is not loosened, it is best to loosen the soil surrounding the plant where you are watering to encourage growth at distances that will support top growth.

Q: My cassia is full of beautiful yellow blooms. This is the first year this 2-year-old plant has done this. When do I trim it back and how far? What type of fertilizer will it need?

A: Shrubs or other plants should be pruned soon after they flower. In spring-flowering plants the flowers are produced during the late summer and fall months. Some finish maturing in the spring before they flower.

Regardless, if these spring-flowering shrubs are winter pruned with a hedge shears, it will remove the spring flowers. If shrubs are pruned properly , they can be winter pruned. Hedge shears should be reserved for nonflowering hedges.

Pruning should be done with a few well-placed cuts deep inside the canopy to remove sections of the plant that are crowded, too tall or too wide. Cuts are made where two stems join together, removing the offensive stem.

Removing larger-diameter wood results in a general thinning of the shrub; it renews the shrub and helps keep it young. I hope this helps.

Q: I have a cassia at the corner of my house to block the street view of my air-conditioning unit. The whole center section has died. I’m beginning to cut out the dead limbs. I check the cuts but am not seeing any green at the bark. Is there a chance that partially cut back limbs might still produce new growth? Or should I cut back to the main trunk? With no center section it looks ugly. Can I hope the living branches will fill in eventually?  Should I dig it out and replant with a new one?

A: It is possible you had some winter kill, but this doesn’t sound like winter kill. Winter kill is most common on new growth, such as the tips of branches, if temperatures are just below their tolerance. If temperatures are considerably below their tolerance, then you also will see death in the older, larger-diameter wood.

It is odd if it is just damaging the interior wood and leaving other parts of the plant alone. Another possibility is root rot if it is watered too often or the area is flooded. This should be fairly easy to determine by pulling the top of the plant toward you and looking at the base of the plant.

In cases of root rot, when you pull on it the base will move around .

For healthy plants you should be able to scrape the soft outer bark with your fingernail and see green beneath it. This is not easy to see in all plants, but at least the inner bark should be cream colored or white.

I would not cut anything back at this time. If there is winter damage, then the killing temperatures already pruned it back. If the plant or plant parts are alive, they will show you where to cut after new growth emerges. When it emerges, cut a few inches below the dead part of the limb and into the strong growth, just above a bud or at a crotch (where two stems come together).

If you don’t see any new growth by mid-April, then it is dead.

It is your call whether to remove it or not. With an established root system it should grow back rapidly and will fill in the spots where there is strong sunlight.

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.