3 factors that affect your landscape water use

Many water purveyors supply a graph of your water use over the past 12 months on each water bill. What you know is about 70 percent of that water recorded on that bill is used to irrigate landscapes. The term used is “average landscape water use.”

What affects average landscape water use? If the irrigation system is working and managed perfectly, then three factors govern how much water your landscape uses: the size of the plants, how many there are and their origin. The first two are common sense: Big plants use more water than little plants, and more plants use more water than fewer plants. How big the plant gets is common knowledge, but oftentimes the information is ignored.

The third factor, its origin or where it comes from, is important because it hints at how well the plant will handle our desert sun, heat, cold, humidity and wind. Sometimes the common name provides clues: Japanese privet, Carolina jasmine or Mediterranean palm. Sometimes they don’t, such as mock orange, pyracanth or heavenly bamboo.

But if you think about it, it’s common sense as well. Plants that come from dry or desert regions, sometimes called desert plants and can give consumers a bad image, can use less water when given the chance. It’s not magic. Desert plants are water guzzlers when overwatered.

Be informed when you buy plants. Sure, they look good when first bought. They usually grow well in the first four or five years unless they are stuck in some brutal location they can’t handle.

When landscapes become 5 to 10 years old is when plants show their true identity. What size will the plants selected grow to at maturity? Were too many plants bought and planted? Will the plants selected tolerate growing in soils covered in rock? Unless you do the homework, you will find out during the first summer or in four to five years.

Q: Last weekend we removed the front half of our lawn. In the middle of the lawn is a 15-year-old Chilean mesquite that never had a problem. During grass removal, its roots were chopped. Drip emitters are now supplying the water to this tree. Will the tree be OK now that its front half sits in rock with only drip emitters providing water?

A: Whenever roots are cut off or removed from plants, some of its top should be removed as well. That compensates for the loss in roots the tree had.

The tree establishes what is called a root-to-shoot ratio, basically an equilibrium between the roots and the top growth. If the equilibrium is unbalanced (in this case the tree’s roots were chopped off), then the tree must grow new roots to establish a new balance between its roots and shoots — a new root-to-shoot ratio.

But when roots are removed, a part of the top should be removed to help the tree establish a new equilibrium. In your case, the top of the tree needs to be pruned.

Secondly, with the lawn providing water to the tree, the roots can grow wherever they want. If you mentally spin a circle the height of the tree over the lawn area, it roughly describes where its roots could grow.

Irrigation water should be applied to as much of this lawn area under the tree as possible. This encourages the growth of new roots to a large enough area. If pruning and adequate watering are done, the tree will have as little damage to the top as possible.

Using six to 10 drip emitters will not provide enough water to large trees. The area where water is applied will be too small.

I would suggest coiling drip tubing under the tree and covering as much area under the tree as possible to provide water to a large enough area. Make sure when the water is applied that enough minutes are used to wet the soil to a depth of 24 inches. All of this is important: enough emitters, enough area watered and enough minutes.

Q: We recently had our backyard landscaped. We had a plum tree planted in one corner. It did OK for a few days, and then it lost all its leaves. It was getting water. A few sprouts from the base are coming up but nothing else. Is it dead or just been shocked by the transplant?

A: Hard to say, but the usual reason for leaves dropping from the tree and suckers growing from the base is because the tree’s roots were dry either in the container or when they were planted directly into a planting hole. Always plant wet. I suggest planting it directly from a wet container into a wet planting hole with very little time in between.

During the spring and fall months when temperatures are cooler is the best time for planting. There are many things that can go wrong during the summer heat, which can cause leaves to drop, particularly if it is windy.

The best time to plant is in the morning when the weather is cool and very little wind. The absolute best time is when it is overcast, but that seldom happens here.

Transplant shock can happen to landscape plants, but it doesn’t have to happen. If the plant in the container is watered daily and the tree is planted directly into wet soil, then there should be no leaf drop.

Q: In your column, you suggested that turning off the water to fruit trees could force dormancy this time of the year. How long should the water be shut off to force dormancy?

A: Plants respond to stress. If they are stressed by a lack of water for a few days, then that will do it. It appears that stress to plants is just simply stress, whether it is from a lack of water or cold temperatures. In fact, in some plants, dry soils can cause the same leaf drop as cold temperatures.

How long to wait? It really depends on the soil moisture and the plants. If the soil becomes too dry, it is possible to damage the plants from drought. If the soil stays too wet, then leaves will not drop.

So the soil moisture has to be managed. Much of it is experience and developing a “green thumb.” When soil moisture around fruit trees reaches about 20 percent of applied water should do it. A soil moisture meter registering around an average of “2” when the tip is pushed into the soil about 4 to 6 inches deep should do it.

Q: I investigated other trees and am now considering a Texas ebony. What is your opinion of this tree?

A: It is a nice tree, It can get big but takes a long time to get there. Texas ebony grows to about 40 feet tall and 40 feet wide, so give it plenty of room. It’s thought to be a small tree, but it’s not. It just grows slowly.

Don’t let just anyone trim it. Landscape maintenance companies like to destroy them with hedge shears. If a certified arborist does it right, it should be pruned once every three or four years.

When it flowers in the spring, it attracts a lot of bees. It’s evergreen until temperatures hit the mid-20s, and then becomes deciduous, so it is considered semi-deciduous in our climate. In the warmer climates of Laughlin and Phoenix, it should stay evergreen all through the winter.

Its negatives are its large size when mature, slow growth and large seed pods that can be somewhat ugly and messy. I would use it on the west side of a dry landscape to shade a two-story house or as a visual screen between properties.

It is a Chihuahuan desert native coming from dry areas just south of west Texas. What does that tell us about watering it? Water it at the same time as other desert native plants.

For an eventual medium-sized evergreen tree, it doesn’t use a lot of water. If you water it the right way, it should be easy on the pocketbook.

Water it deep and wide and then hold off on it until leaves begin dropping and then water it again. It can go for at least a month between irrigations in the summer.

It will be fine growing in landscape rock with other desert natives like Texas sage, beargrass, Dasylirion (sotol) and agaves. It should also do well planted as a slow-growing visual screen between properties.

So, if you have the room for it and can find it, plant it.

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.