Issue: November 8, 1999

Why isn't this a xeriscape?

I have converted my landscape to xeriscape to reduce water use as I have heard recommended many times. However, I am told that my landscape is not a xeriscape. I spent a lot of money on rock, gravel, and colorful concrete paving stones. Why isn't my landscape a xeriscape? Enclosed is a photo of my expensive new landscape.

Your photo reveals a landscape often called "Southwest landscaping" and sometimes incorrectly called "Xeriscape." Your landscape is predominantly gravel and hard paving with little landscaping in the sense of living plant material. When we teach about xeriscapes, we include consideration of the livability and living aspects of the landscape. If you look at the natural landscape of New Mexico and other areas of the Southwest, you will notice that these landscapes are full of life. These native landscapes include many native grasses, shrubs, and flowering plants. They provide habitat for birds and other animals. The rock landscape you have described is very different from such natural landscapes. That is why your landscape is not considered a xeriscape by all who see it.

The rocks and other hard materials may be a part of a xeriscape, but there is a greater use of living elements in a xeriscape. In a xeriscape there will be many plants utilizing the rocks and other mulching materials as a mulch to reduce moisture loss, to maintain uniform soil temperatures, and to restrict weed growth. In time the mulches will be relatively unseen as the plants grow and cover them. With plant cover, the temperatures of the landscape will be lower than the purely rock landscape.

It is true that a rock landscape reduces water use in the landscape, but the increased water use in a swamp cooler decreases the benefits of landscape water savings. A rock landscape may have lower maintenance requirements than a xeriscape, but the difference may not be as much as you expect. Dust and leaves collect in the rocks. As the rock area fills with dust, weeds are able to grow and require removal as do leaves which blow in and accumulate between the rocks.

As you can see, as a horticulturist I favor a landscape with more plant material. To me, it is much more beautiful and interesting. A true xeriscape is just such a landscape. However, I acknowledge that there are those who like the rock landscapes. The major conflict is the use of the term "xeriscape" to describe the rockscape.

Backflow preventers

I just had a new irrigation system installed in my landscape. They put in some pipes that stick up in the air. I am afraid that the water in these pipes will freeze. Why did they do that?

According to Willie West, licensed irrigation contractor and member of the New Mexico Irrigation Association, the pipes you describe sticking out of the ground are the backflow preventers which prevent contamination of the city water supply and the water you drink in your home from contamination by water from the landscape which may contain fertilizers or pesticides.

Willie points out that this protection is provided only if the system is installed properly. He says that unfortunately there are many ways to install the backflow preventers improperly. If they are installed properly, they provide protection and most of the backflow preventer types will not require winterizing.

A properly installed system consists of below-ground valves, positioned below the depth of frost in the soil with the backflow preventer positioned "downstream" from the valves so that water drains from them when the valves close. For this to happen, it is important that the all-metal (brass, copper, and galvanized pipe) backflow preventer be elevated higher than the highest point of use; that is, the backflow preventer must be above the highest sprinkler head or drip emitter. If this is not the case, the backflow preventer is improperly installed and is subject to winter damage failure in its purpose of protecting your water supply. This requirement that it be above the highest point of use explains why these pipes are above the ground.

If your have any other questions or problems regarding your backflow prevention device or any other part of your irrigation system, please contact a properly licensed and insured irrigation contractor.

Marisa Y. Thompson, PhD, is the Extension Horticulture Specialist, in the Department of Extension Plant Sciences at the New Mexico State University Los Lunas Agricultural Science Center, email: desertblooms@nmsu.edu, office: 505-865-7340, ext. 113.

For more gardening information, visit the NMSU Extension Horticulture page at Desert Blooms and the NMSU Horticulture Publications page.

Send gardening questions to Southwest Yard and Garden - Attn: Dr. Marisa Thompson at desertblooms@nmsu.edu, or at the Desert Blooms Facebook.

Please copy your County Extension Agent and indicate your county of residence when you submit your question!