Resources For Drought Tolerant Plants

California is heading into a fourth dry year. In January 2014 the governor proclaimed a drought state of emergency and called on Californians to cut their water use by 20 percent. Water is getting scarcer and dearer across much of the West, and outdoor watering is usually the first use to be cut. That makes plant choice one of the most effective water decisions a gardener can make.

Drought tolerant planting does not have to mean gravel and cactus. Many shrubs, perennials, grasses and trees from dry climates are full, colorful and long-lived, and gardens built around them can look as generous as any lawn and border.

What drought tolerant means

A drought tolerant plant is one that survives long dry periods with little or no supplemental water once it is established. Such plants manage it in different ways: small, gray or silvery leaves covered with fine hairs that reflect sun and slow water loss, waxy coatings, fleshy leaves and stems that store water, deep or wide-ranging roots, or the ability to go dormant through the dry season and recover with the rain.

The qualifier that matters is “once established.” Every new plant, however tough, needs regular deep watering while its roots grow out into the surrounding soil, typically through its first one to three growing seasons. A common reason water-wise plantings fail in their first summer is that they were treated as established on the day they went in. Planting in fall, where winters are mild, lets roots grow through the cool, wet months before the first summer arrives.

Why the hardiness zone is not enough

Plant labels and catalogs usually list a USDA hardiness zone. That zone is based on the average of each winter’s lowest temperature at a location and says only whether a plant is likely to survive the cold. It tells you nothing about rainfall, summer heat, humidity or soil. A plant hardy to your zone may need far more summer water than your climate supplies.

Being native to North America is not enough either. Plants from stream banks and moist woodland are native too, and they need steady water. What matters is a match between the plant’s home climate and yours, whether it comes from your region or from a similar climate elsewhere, such as the Mediterranean, central Chile or South Africa for coastal California.

Where to find a list for your region

Extension services and Master Gardeners

Most state extension services and county Master Gardener programs publish lists of plants that cope with local conditions, often with notes on soil and exposure. Your county extension office is the place to ask.

Water utilities

Many water providers in dry regions publish low-water plant lists, run demonstration gardens and offer advice on converting lawns. Denver Water coined the word xeriscape in 1981 for exactly this kind of landscaping.

Public gardens and arboreta

University arboreta and botanic gardens trial plants under local conditions and publish lists of the ones that have performed with little water.

State plant classifications

In California, the Water Use Classification of Landscape Species, compiled through the University of California, rates thousands of landscape plants by how much water they need in each of the state’s climate regions.

Native plant societies

State and regional native plant societies keep lists of local species for gardens, with information on where each grows naturally.

Planting for less water

Whatever list you use, group plants with similar water needs together so that the thirsty ones can be watered without overwatering the rest. Improve the soil with organic matter before planting, mulch the beds, and water deeply and infrequently once plants are established so roots grow down rather than staying near the surface.

Since then, the USDA has released a new Plant Hardiness Zone Map, in November 2023, its first update since 2012; about half the country moved into the next warmer half zone.