Xeriscaping

Just like people perspire, plants also give off water in the form of evaporation, and some are better equipped for and do better in arid regions than others.

Drought-tolerant plants are those that use water more efficiently; they store it better, they keep it longer by using it wisely, they give up less of it to the air around them. They also have ways of finding all the available water in an area and preventing other plants from encroaching on their territories.

Many drought-tolerant species have grey, waxy, fuzzy/hairy, shiny, sticky, or thick, leathery leaves. They have fewer pores, or stomata, to prevent evapotranspiration - the process by which plants draw up water from the ground through their roots, move it through their stems and leaves, and then eventually lose it to the air as it evaporates from their leaves and flowers. Some orient their leaves to minimize exposure to sun. Hair or fuzz on leaves helps to provide warmth and to stem the flow of drying air. Sticky leaves and stems retain water. And some plants drop their leaves entirely, to minimize surface area, and thus, the amount of water lost to the environment.

Root systems are another way plants thrive when there's no water. Some have vast networks of shallow roots to gather surface water. Others have large, tuberous roots which act as storage tanks for the water they gather during the rainy season. And some have extremely deep-reaching taproots to find the water trapped further down in the soil - water other plants can't reach.

Sometimes merely finding water isn't enough - plants must also compete for soil area. Many of those plants with shallow root systems take a proactive approach to water gathering and set chemical boundaries to prevent other plants from encroaching on their territories.

There are several ways to retain moisture and help your plants retain water.

Use drip irrigation and water after sunset once the heat of day has passed. Watering at night helps cut evaporation and gives plants longer to absorb moisture before the heat of day burns it away.

Mulch. It helps cut both evaporation and weeds. Plus, it looks fabulous in most Mediterranean gardens and gives a well-manicured appearance.

Add organic matter (ie. compost, manure mixes, sphagnum/peat moss) to the soil. If you have acid-loving plants, pine needles also make a great planting material and are very easy to come by, if you live in an area with a lot of pine trees. Sphagnum can also acidify the soil, so check your garden book to find out which of your plants like or will tolerate acidic soil.

Plant trees and larger shrubs to create shade.

Use dense plantings and decorative walls to break up airflow/wind.

Use an automatic watering system and low-volume heads. Make sure your sprinkler system and/or tubing are in good repair and working properly. Don't overwater.

It's really not hard to choose low-water need and drought-tolerant plants, if you consider the origin of the plants in question. A great many of the plants used in xeriscape gardening come from arid regions of the world, as well as the indigenous plants local to your area. Plants from South Africa, Australia, Madagascar, Mexico, Italy, Greece, Turkey, Spain, the American Southwest and High Deserts of the western US tend to be excellent choices. It is not a given that a plant from a particular region will be drought-tolerant, however, so be sure to look up the needs of plants before you buy!

Assuming you don't know a plant's origin, when you're looking at plants, go for those that require little or no to moderate watering. Avoid those that need heavy, regular, or moderate to regular water, as they tend not to do well in a dry spell, especially in the heat of summer. If you live in an area that gets rain regularly, even during summer, you can probably choose plants that need moderate to regular water and be fine, but if you hit a dry spell, you should give them supplemental water, as those plants are not actually drought-tolerant, they just don't generally need additional water in your area. They are not, strictly speaking, xeriscape plants.