Garden roses struggle when temperatures rise

This is the time of year when garden roses struggle. As temperatures rise, roses stop flowering and the leaf edges turn brown and scorch. The month and week they stop flowering depends on their landscape exposure (which direction they are facing in the landscape), how the soil was amended where they were planted, the variety planted and their overall health.

Some plants don’t grow well in rock, and roses are one of them. Nearly all landscape plants in the rose family (think photinia, pyracantha, strawberry, Carolina cherry laurel and most of our favorite fruit trees) like soil improvement and a moist environment when planted in desert soils. The number of native Mojave Desert plants in the rose family is very limited. That tells you something.

The most favorable environment for garden roses in the desert is soil amended with compost at planting, six hours or more of morning sun, organic mulch on the soil surface (like woodchips) and moist soil. Garden roses will not do well the first year after planting if put in the wrong location, the soil is amended poorly and not watered correctly. They will begin failing in three to five years if surrounded by rock.

Applying the right kind of fertilizer at the right time is only part of the success equation. Applying a rose fertilizer once in the spring is adequate, three times during the growing season is better, and it can get complicated from there with fertilizer favorites and soil amendments if you are a rose enthusiast.

Some roses perform better in the hot desert than others. Consult the Cooperative Extension or the Weeks Roses wholesale website for suggested recommended varieties for the desert when buying or replacing. Roses last 20 years or more if properly selected, planted and maintained.

Q: Now that it’s getting hot, my roses have stopped blooming. Should I keep feeding them or wait until the weather cools and they start blooming again? Can it hurt them when feeding in temps over 100?

A: Roses are typically fertilized three times a year and avoiding months when it’s hot (June, July and August). For convenience, I suggest fertilizing on three holidays when cooler: Valentine’s Day, Memorial Day and Labor Day.

On Valentine’s Day soil application, include your favorite iron fertilizer as well. If you apply iron to the soil, only one application is needed. Generally, do not fertilize any plants during the hot months. If fertilizer must be applied during these months, apply it at half strength.

Q: I planted a rose bush facing south as a memorial for my dad and I want to know how to help it along. It has holes in some of its leaves and a few yellow leaves. I saw one grub and I got some stuff to get rid of grubs.

A: Roses in a southern exposure have not had many problems provided they stay healthy. Varieties of roses suited for desert environments handle hot locations well and may bloom throughout the entire winter if planted in the right microclimate. Like all roses, they don’t flower well during the heat, which may start a month early (May) in southern exposure is like yours.

Look at the color of the leaves and the quality of its new growth to judge its general health. New growth should be vigorous and the leaves dark green. These are two signs the plant is healthy and growing. Hopefully, you amended the soil at planting, then used organic mulch on the surface of the soil surrounding them, fertilized them three times a year and watered when they needed it to keep them healthy.

In dry environments like ours, roses have few disease problems and insect problems, mostly occurring in the spring. We may see aphids and flower thrips in the spring and occasionally cane borer, but it’s nothing to be alarmed about.

You will handle these problems when you see them. Grubs feeding on the roots in the spring may occur, and a systemic insecticide drench applied around the roots once a year will take care of them — and aphids at the same time.

The size, shape and position of holes in the leaves tell you a lot about which insect may be causing this. Most commonly it is leafcutter bees.

We may see the same damage on vegetables, basil and other plants with soft, tender leaves. The strategy is the same. We leave these insects alone. They are good pollinators and so we choose to live with that kind of plant damage and understand its meaning.

As far as yellow leaves go, ignore them if they appear on older, bigger stems. If these yellow leaves occur and new growth in full sunlight then we may need to look a little deeper on why.

Q: We would like to plant fruit trees but don’t have much gardening experience. Can we plant during the summer months? Are there types of fruit with a tougher skin so birds can’t get them? My wife loves avocados, so is that a possibility for someone without a green thumb here?

A: I would not plant anything but palm trees, Bermuda grass, cactuses and succulents from May through mid-September. Even good gardeners prefer not to plant during the hot summer months if they have a choice. Nurseries are pretty dead compared with spring.

Why? Anything you plant now is slow recovering from planting because of the late planting date, heat and low humidity. If you see something you just can’t say no to, then buy it, put it in the shade and plant it as soon as possible.

Plant in the morning when temperatures are lower. After removing it from the container, transfer it to a wet, prepared planting hole as quickly as possible. Have a hose ready and plant everything wet, wet, wet.

If you are new to gardening and fruit trees, start with a single fruit tree. Purchase a 5-gallon container tree or larger. Apricot is a good choice and harvest the fruit when they start turning color and you see the first signs of bird nibbles.

You have two to three weeks to harvest everything from the tree, so don’t take it all at once. Fruit will ripen first in the hottest part of the tree and work toward the coolest. So pick the fruit first that is furthest along.

Picked fruit will ripen on your kitchen counter (or garage or back patio and covered so the birds can’t get them) and still taste the same. The fruit doesn’t need light anymore to ripen and taste good. Apricots don’t have to be soft on the tree (which by the way is a little later than when birds first start pecking them) to be tree-ripened.

Don’t start with an avocado tree unless you are an experienced gardener. I am not going to get into the reasons why here, but I will guarantee you failure if you don’t know what you’re doing. Search my blog for answers. Apricot or plum is much easier to grow here than avocado.

Q: I have an ash tree that is 18 years old. This year about 20 percent of the tree has dead branches while the rest looks good. We really do not want this shade tree to die.

A: That tree occupies a very important part of the landscape, I am sure. However, your ash tree may have an incurable disease called ash decline. In California, they call it “ash dieback.”

This disease, so far, is found only on ash trees and causes branches to slowly die in the canopy over several years. You can see this disease in many ash trees in the Las Vegas Valley. But these dieback symptoms are similar to drought.

Before giving up on it, try applying more water to the base of it in a larger area. Along with its normal water application, do this once a week with a hose and sprinkler and see if that helps reduce the problem.

I use a mechanical water timer that costs about $12. I adjust the water delivery from the sprinkler to about the same size as the tree canopy and water for one hour. The water should wet the soil 18 to 24 inches deep when you water. Do this weekly for one to two months.

If the tree starts growing more, then you must apply more water to the tree. If the tree does not respond with new growth, it probably has ash decline. Applying a fertilizer once a year in February is enough for trees.

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.