Without an adequate supply of water, a plant cannot carry on the basic physiological activities such as photosynthesis, respiration and growth. Depending on the plant species, as much as 99% or more of the water absorbed by the roots may be transpired or lost to the atmosphere.

Let’s look at where all the water really goes. We irrigate at the root zone, and even though the water may be absorbed by the plant, much of the water ends up in the air. This function is essential to the life processes of the plants, mostly for cooling. To temper this loss of moisture, especially where the water supply is low or inconsistent as in the arid southwest, native plants are adapted with special organs. In the plants most suitable for Xeriscape, the leaves are perhaps the most highly refined, water-conserving organ. Waxy cuticles, thickened layers, decreased leaf surface, fewer stomata and hairy leaf surfaces are natural modifications within the plant, to allow for greater resistance to moisture stress.

in the plants suitable for Xeriscape, the leaves are perhaps the most highly refined, water conserving organ.

Comparing landscape plants, a tropical plant like Hibiscus with its large, shiny leaf surface is simply not geared for drought. A better choice for a dry area would be Matilija Poppy (Romneya coulteri), for bloom, or Sugarbush (Rhus ovata) for form Sugarbush with a waxy cuticle and Matilija Poppy, with a somewhat fuzzy gray leaf and summer dormancy, are perfectly suited to our dry summers. Many dryland plants such as Eucalyptus species as well as some native plants such as Jojoba (Simmondsia chinensis) have their leaves oriented in a vertical fashion. In this way, they receive the full sunlight obliquely, rather than directly and thus do not become as heated. Some leguminous plants such as Cassia species have adopted a procedure of folding up their leaflets to reduce transpiration, and lighVheat absorption.

Leaf litter, often so diligently removed by the well-intending gardener, is usually the plant’s strongest account in water economy. The cooling mulch, self-produced by Acacia, Eucalyptus, Lyonothamnus, Oaks and others, locks in soil moisture during the dry season, while providing shade on the soil. With time, this litter breaks down to provide nutrients for the plant.

Leaf litter is usually the plant?EUR??,,????'???s strongest account in water economy

At the leaf modification extreme, some xerophytes such as the cactus and succulents are entirely leafless, their strategy for water conservation is water storage. Others such as California Buckeye (Aesculus californica) are drought deciduous; their branches are naked in late summer. Plants like I Palo Verde and Mesquite get by in arid regions with tiny leaflets on a compound leaf. However, since the total leaf surface is rather small, nature added old green stems and trunks to aid in photosynthesis without transpiring precious water.

While xerophytes are the truly, drought-loving plants, botanists refer to the hard-leaved evergreen shrubs adapted to Mediterranean climates of the world as sclerophytes. Examples of sclerophytes are Grevillea from, Australia, Protea from South Africa, and Arctostaphylos from California. Interestingly, some of the prettiest flowering shrubs in the world are in this category of plants. It seems that the Mediterranean climate regions have been specially blessed with a great variety of beautiful “hard-leaved” shrubs?EUR??,,????'??? nice foliage and excellent flowers. For water conservation in today’s landscape, the horticultural professional can just “Leaf it to Xeriscape plants.”

Mike Evans is co-owner of the Tree of Life Nursery, wholesale growers of California native plants in San Juan Capistrano. He has served on the Xeriscape Committee in California since its foundation.