Nearly every landscaper and gardener brags about using plants that do not need much water. Buzz words like “drought tolerant,” “native,” “sustainable” and “xeriscape” have become all too common, even though few actually spell “xeriscape” properly – it is not “zeroscape.” Unfortunately, though, most gardeners water so frequently and generously that drought tolerant and native plants are less sustainable than plants that want more water.
The difficulty is that drought tolerant plants generally need rather regular watering immediately after planting, while they are still dispersing their roots, but then want to dry out between watering once they are established. Otherwise, they are very susceptible to rot if the soil is constantly moist.
Trees like incense cedar, beefwood, silk oak, olive, California pepper tree and some types of eucalyptus, pine and oak can be nice shade trees in lawns that are not watered too much, but do not live as long as they would with less water. California laurel, African sumac, Australian willow, strawberry tree and most acacia and cypress are less tolerant of lawn irrigation.
Bottlebrush, oleander, cotoneaster, hop bush, firethorn, grevillea, some types of wild lilac (ceanothus) and all sorts of juniper can be happy with or without regular watering. Manzanita, coyote brush, rockrose, flannel bush and western redbud really want to dry out between watering. Like many plants from arid climates, wild lilac, coyote brush, rockrose, flannel bush and western redbud are naturally relatively short lived.
Lily-of-the-Nile is one of the most useful perennials, and can survive with annual rainfall or nearly saturated conditions. New Zealand flax is nearly as adaptable, but is more susceptible to rot if watered too much. Rosemary and several iceplants are nice ground covers with or without regular watering.
The various yuccas, aloes, agaves and their other relatives are some of the most practical perennials for arid climates, and many tolerate somewhat generous watering if necessary. However, most agaves and yuccas have nasty sharp leaves; and some agaves get too big to keep at a safe distance. Also, their bold personalities are not adaptable to every garden style.
Highlight: Century Plant
The horridly sharp and stiff terminal spines, and the nastily stout marginal teeth of the big leaves of century plant, Agave Americana, are very intimidating. Individual leaves can get about six feet long, and are arranged in rosettes that can get more than twice as broad, so need plenty of space at a safe distance. Many century plants have metallic gray foliage. Others are variegated with various white or yellow stripes. The imposingly tall flower stalk that eventually emerges from the center of each rosette can be as striking as the foliage is. Vigorous stalks can get taller than 20 feet. The yellow flowers are too high to be seen closely, and are protected by even more thorny nastiness. Each rosette dies after bloom, and eventually needs to be removed as wickedly barbed pups (basal offshoots) begin to develop around it. Abundant pups can easily develop into a wicked thicket if not thinned.