Cut back on watering desert trees


Here are some questions from readers for which I asked Paul Noe of Star Nursery to provide answers.

Q: Will overwatering all drought tolerant trees cause them to produce a lot of excessive top growth like African sumacs?

A: We all overwater our desert trees and it creates lots of unnecessary top growth, finds the specialist. The University of Arizona found the only time desert trees grew top growth is when it rains. After it dries the roots begin searching for nutrients.

Here is the take home message: We water desert trees several times a week signaling plants to grow more. This causes the interior leaves to shed because they can’t get enough light to function and the roots never get a chance to grow. So cut back on their water.

Here’s an actual example of overwatering. Dennis Swartzell of Horticulture Consultants loves to tell about pruning mesquites four times a year. All he did was cut back on the water and only had to prune once a year.

Q: Why are our hackberry tree limbs dying?

A: Hackberries do this as they age, Noe says. It usually means poor drainage or caliche causing the tree to struggle. “To correct the problem, purchase a soil penetrant that penetrates our alkaline soils to open up the soil for your tree.”

Also check the limbs for a borer invasion. Look for BB size holes in the bark. Pull the bark back and look for their damage of zigzagging galleries filled with sawdust as your indicator in the cambium layer. Find out how far down they’re working and cut out all the above and destroy it. Depending on the infestation the trees will come back as they are tough.

If the remaining larger limbs are exposed to the sun, paint them with white water-base-latex paint to deter the bores. Failing to do this, the exposed wood sunburns and becomes an invitation for more borers.

Q: Please recommend some herbs for Las Vegas?

A: Just about all herbs do well in Las Vegas, the horticulturist said. Provide them with a highly organic soil with good drainage. Plant them on the morning side of the house or at least provide afternoon shade during the summer. Keep them well watered. They also do very well in containers, so plant them near your back door.

For a list of herbs that do well here, call the Cooperative Extension at 702-257-5555 for its free “Beginning Desert Gardening” handbook.

Q: The elm beetles defoliated our elm tree. Is there anything to control them?

A: Try Bayer’s Tree and Shrub Insect Control, Noe says. It is a systemic, meaning it works within plants to get the bugs as they feed on the leaves. Apply this to the ground now and it will be waiting in the leaves when the bugs start munching.

Q: We planted a podocarpus last March on the south side of the house and it suffered from leaf scorch and looks a mess.

A: It’s a great vertical shrub for our landscapes providing you plant it on the morning side of the house. The south exposure caused the leaves to scorch especially on those 110 degree days, says they expert. Pop it out of the ground and plant in an area free from the afternoon heat or it will be a perennial problem.

Q: What can we do? Our Hall’s honeysuckle is consuming a metal screen attached to our home and there were only a few blooms.

A: Prune it, says the expert, and prune it hard. It will come back for you but it won’t have many blooms this summer. Cut it back to the height you want. Then keep nipping the extending branch to keep them in check. It’s also a good idea to clean all the dead wood out and let the plant start up again.

By letting it grow, it puts all its energy into growing vines instead of flowers. Overfertilizing and overwatering also will inhibit blooming.

Q: Why are our oranges so mealy?

A: That’s brought on by water stress. Noe says water is critical as the fruit is finishing off before harvest.

Q: How do I care for photinias?

A: Don’t prune photinias until after the leaves turn green to get the maximum beauty out of them. Through the summer, nip at the extending branches to keep them in bounds.

Linn Mills’ garden column appears on Sundays. You can reached him at linnmillslv@gmail.com or call him at 702-526-1495.