Check for borers after rainfall

It rained most of the day last Saturday in Las Vegas. The following Sunday would have been an excellent time to look for borers in the trunk and limbs of landscape plants. Their presence would be announced by sap oozing from these infested but water-softened locations, even though no visual damage is apparent.

If you see sap oozing from landscape plants and fruit trees, it’s a good time to dig into those areas with a sanitized knife to see if you can find this critter and remove it. This will prevent its continued damage this spring and summer. Otherwise, you might find a dead limb or two or worse in July or August.

After a rain, mushrooms appear in a few days wherever wood is rotting on the surface of the soil or underneath it. You’ll see them popping up through wood chip mulch and where dead roots of trees might have rotted. Water helps dead wood rot and disintegrate into the soil where the mushroom mycelia grow. This rotting adds organic matter to the soil, encouraging roots to grow and causing the soil to become dark brown and rich.

Just like desert wildflowers, mushrooms pop up quickly to spread their seeds everywhere in a couple of days after a rain. These mushrooms stay fresh only a couple of days before they mature and die.

Sometimes mushrooms form beneath the soil like huge, fleshy alien balls and then pop open at the surface, releasing their spores. As soon as you see these mushrooms, knock them over with a rake or smash them with your foot. Dogs can become sick if they eat them.

Rain changes everything in the desert. Desert soils are dry soils and not meant to be constantly wet. When desert soils become wet, I think of them as unstable both structurally and chemically.

An infrequent desert rain is not a problem. But when irrigation water is applied over and over to a soil that is normally dry, these soils shift, collapse and chemically change. In urban landscapes, this can be potentially destructive.

This is the reason for keeping irrigation water 3 feet away from the foundation of a home, patio, driveway, wall or sidewalk. Corrosive salts are in the soils and irrigation water. These corrosive salts will eat away at cement and steel.

Salts in the soil dissolve when water is present, causing the soil to collapse over time. Water dissolves these salts and carries it as far as it reaches and then deposits it in straight lines or circles.

When the same amount of water is applied over and over, the salts are deposited to the same spot each time. These are the white rings and lines you see on cement and block walls.

Q: Is it possible to grow azaleas in the Mojave Desert? We want to get more color in our yard, and having lived in the East for many years, we know that azaleas add an abundance of color in the spring. I have terrible soil, so I know I would need to drastically amend the soil. Suggestions or comments?

A: You can grow any plant in the Mojave Desert, including azaleas. It’s a matter of how much you want them, because plants that don’t belong here, like azaleas, cost more to maintain. These nondesert plants struggle in our climate and force you to take care of them if you want them to succeed.

My second point is that your sense of place has never changed. You are still thinking like an Easterner. You live in the Mojave Desert now. It’s time to adjust.

Your sense of place relates to where you think of as home. I remember moving from the Midwest to the dry Western states many years ago and missing all the greenery. After adjusting to this new home, I found all of the greenery hurting my eyes on return visits. It was just too green.

After an adjustment period, my new sense of home was the dry Western United States, the different shades of brown, pink, purple and yellow I saw in rock. Plants were found sparingly.

Before I tell you how to grow an azalea here, consider desert perennials that grow easily in the desert and add color. They are easier to grow, require less frequent watering and still provide a great deal of seasonal color.

I am talking about colorful plants such as penstemon, sage, salvia and others. Many of these desert or desert-adapted perennials provide a great deal of color at different times of the year, and most like lots of sunlight.

A good place to look for these plants is online before you go shopping. Get familiar with these names of desert perennials, because it can get confusing at the nursery. Try looking online at the Southern Nevada Water Authority searchable database of plants and the Arizona Municipal Water Users Association database. Become familiar with their recommended plant lists and the plants they recommend. Once you do that, then it’s time to go shopping.

Now to your azaleas. Azaleas are considered an ericaceous plant. This means they prefer acidic soils, not alkaline desert soils. Prepare to add a chemical amendment to the soil to acidify it, such as aluminum sulfate. Aluminum sulfate is much more powerful in its soil acidification properties than soil sulfur. You will probably need to add it to the soil once or twice a year to adjust the alkalinity.

One of the ways that azaleas tell you there is a soil problem is by its yellowing leaves or a brown scorchy edge. By the way, if you end up using sulfur, make sure it is a sulfur powder and not sulfur granules, sometimes called soil sulfur. The sulfur powder reacts much faster with warm, wet soil than soil sulfur as granules.

Azaleas also like lots of woody debris, leaf litter and organic soils, so using compost as a soil amendment and covering the soil with wood chips will be a good first step.

Select a cool microclimate in the landscape that is shady but still bright. Azaleas never like intense sunlight. North exposure or early morning sunlight with shade the rest of the day might be a good choice.

Filtered light is preferred, never direct sunlight. Under the shade of a tree but lots of reflected light is a good spot.

Stay away from planting azaleas that were gifted in pots. These are greenhouse azaleas and not a good choice for landscapes in most cases.

Q: When should I prune a “salad” tree? Mine has five varieties of lemons and two oranges and is almost 5 years old. I am afraid of pruning the wrong branches and affecting the varieties and yield.

A: Pruning a salad tree is more difficult than a fruit tree with only a single type of fruit growing on it. Think of your salad tree having different fruit growing on it, all sharing a common trunk or large limb. When pruning, it is important to remember that each type of fruit growing on that tree needs its own space.

Some types of lemons and oranges have stronger growth than others. Your job when pruning is to prune back the strongest growth of those varieties so that the weaker varieties can survive. Otherwise, the weaker varieties will die out from competition, and only the strongest growing varieties will survive. This is the main reason why salad trees end up with two or three varieties that survive after a few years.

Your job is to be the chief mediator or referee when pruning. When you bought the tree, each of the varieties had a label so that you knew where they were located. It’s important to keep these labels up to date so you see where different varieties are located. This helps to create space for new growth when pruning. It also teaches you which varieties are stronger than others.

Citrus, in general, is easy to prune. Pruning is done immediately after harvest. Any suckers are removed from the main trunk up to a height of about 18 inches.

The canopy, or top of the tree, does not need extensive pruning. If crossing limbs are found, the offensive limb is removed at the trunk or a major limb. If a limb is growing on top of another limb, one of them is removed in the same way.

Rather than a fruit salad tree for small landscapes, I prefer to grow individual trees planted close together; this is sometimes referred to as “planting in the same hole.” These individual trees are pruned separately so that they occupy their own spaces. The result is the same — smaller harvests at different times of the year, but the pruning is much easier.

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.