The mature size of trees, shrubs, and
other plants, how many there are, and their origin determines the amount of
water required to support your desert landscape. Once a landscape design is finished,
the amount of water it needs is fixed. It cannot be changed without consequences. It is set. You won’t be able to change
the amount it needs, by much, without removing plants or replacing them with others.
 |
| Count the number of plants used, their size at maturity and the kinds of plants and their water use and the amount of water needed in a landscape is a done deal. |
Massive trees like Aleppo pine, poplars
and cottonwoods, and lacebark elm require deep irrigations and more water;
water should be applied to wet the soil 3 feet deep or more for large trees; medium-sized
trees like chitalpa, ash, and African sumac should be watered 24 inches deep,
and small trees like desert willow, Texas mountain laurel and California redbud
18 inches deep. Their depth of rooting affects their health and resistance to
heat damage. The same goes for shrubs of a similar size.
 |
| The only way to get roots of plants deep is to water them less often. That must be done with an irrigation valve. |
As the number of plants used in the
landscape increases, the more water is needed. Maybe not in the beginning when they
are cute and small but when they get bigger. Also, the amount of water they need
is not necessarily additive because planting them close together can affect
each other’s water use. In other words, two ash trees planted close together affects
the sunlight, wind, irrigation and other things that impact their individual water
use.
 |
| Growing trees that want to have deep roots in a lawn that must be watered daily in the summer forces trees like this ash to grow roots near the soil surface to get air. Deep soil in lawns doesn’t have any. |
The “type” of trees, whether they are
mesic or xeric, also affect how they respond to applied water. Mesic trees and
plants originate from wet climates (think oleander, palms, iris). These plants
don’t do as well when water is in short supply. They cannot grow and leaf out
quickly after a drought as xeric trees and shrubs can (think acacia, Texas
mountain laurel, penstemon). Xeric plants have “coping mechanisms” that handle
water shortages (like shedding leaves or slowing growth).
 |
| Growing desert plants with other desert plants (xeric) allows you to use a similar watering schedule…less often but lots when they do get water. That’s what irrigation valves do. They turn water on and off. This allows for different irrigation frequencies. |
Xeric plants can be coaxed into using less
water and then respond quickly with strong growth and increased density when
water is available. But many xeric plants are sensitive to heavy daily
waterings, particularly during high temperatures. But xeric plants offer the
best opportunities for water savings. Most water savings with xeric plants
happens because of less frequent watering rather than the amount of water applied.
 |
| Sweet acacia can be watered less often than mesic trees, thus saving water. How do I know when to water this tree? When it is not as dense as it was when earlier in the year. It needs water. About a week after an irrigation the leaves create dense shade again. |
You can have the best irrigation system and
plants in the world, but if you apply the water wrong it still results in
water waste.