The West Coast swings from drought to flood, from El Niño to La Niña. What is a gardener to do?
It’s hard to know how to garden sustainably in a climate where rainfall averages are remarkably consistent over any 15-year period, but a year-to-year graph looks like it was drawn by a yo-yo. We are told to use drought-tolerant plants, but in a region where five to nine months of no rain is normal and rainfall averages anywhere from 10 to 40 inches from south to north, the term drought-tolerant plant is nearly useless. All plants are drought tolerant in their native habitat. For successful gardening, we should be thinking about climate-tolerant plants, then go about defining the climate.
But it is hard to define this climate or even its geographic limits. We have learned to call it a mediterranean climate, but if that simply means relatively mild, wet winters and hot, dry summers then much of the entire West Coast qualifies from Palm Springs to Spokane. Gardeners in Santa Fe, Denver, and Boise say they use mediterranean plants but few plants are suitable to all these cities.
The garden editors at Sunset Magazine—the most reliable source of garden information for the western United States—recognized the wide range of microclimates and divided up the region into 24 zones that are little understood by anyone outside of their own zone. Maybe we should go beyond mediterranean and simply call this entire region summer-dry or what Sean Hogan at Cistus Nursery in Oregon calls a winter rainfall climate.
No matter what we call our climate broadly, we need to recognize the variables that affect which plants we choose. There is tremendous diversity in rainfall, high and low temperatures, soil, evapotranspiration, and microclimate created by hills, coastal fog, or hot Santa Ana winds throughout the Pacific Coast.
Considering climate qualifiers
Nevin Smith of Suncrest Nurseries calls these local variables qualifiers that we can use to understand our specific conditions, no matter how we define the climate. To call our winters mild and wet or summers hot and dry does not qualify how wet for how long or how hot a plant can tolerate. The art and science of gardening is discovering which plants play well together in our own gardens with our own qualifiers.
Gardeners in all climates recognize the wisdom of using climate-tolerant plants, particularly in an era where sustainability has become an important consideration. It is an especially exciting time to be a gardener in a summer-dry climate as we begin to appreciate the natural aesthetic of our region. There are so many new plants coming from other summer-dry regions that can be used in untried combinations—so much to learn as we experiment.
Some of the new plant introductions are coming in from the margins of summer-dry regions. Many wonderful Salvia selections of S. gregii and S. microphylla are coming from the deserts of the Southwest and Mexico. These plants get some summer rain in their native habitat but adjust beautifully in summer-dry gardens.
Jo O’Connell of Australian Native Plant Nursery finds many of the best garden plants in California are from eastern Australia—Westringia, Grevillea, Eremophila. These plants evolved with extreme shifts in climate outside of the predictable summer-dry areas of the continent.
From other parts of the world, we see hardy succulents such as Delosperma from the mountains of South Africa (rather than the summer-dry fynbos) and trees such as Luma apiculata from the forests of Southern Chile—not the drier matorral.
And then there are the amazing California native plants in the California Floristic Province, one of the 33 biodiversity hotspots on Earth with 3,500 different species of plants, 61 percent of which are endemic. Perhaps the most exciting development for gardeners is the diversity of California native plants that nurseries are selecting and selling. Bart O’Brien, Manager of Regional Parks Botanical Garden in Northern California and former head of horticulture at Rancho Santa Ana Botanical Garden in Southern California, points out there are many more creative options available to gardeners who use native plants because the genetic diversity has not been bred out of them in the nursery trade. A plant will respond differently in different gardens depending on which of the dozens of native plant nurseries may be propagating it.
An emerging garden aesthetic
As clever gardeners learn to use all these plants from other summer-dry regions, a climate-tolerant garden picture emerges. It is a shifting aesthetic determined not by climate label or garden magazine mimicry but by gardeners themselves, garden by garden, city to city, using qualifiers as Nevin Smith suggests—and the process has been accelerated by drought.
Until a few decades ago, California gardeners did not worry about water. The state was considered a gardener’s paradise where anything could grow. The winter rains and snows stored ample water even in dry years. Our lawns became the model by which the rest of America judged beauty. Lush tropical gardens were everywhere.
How things have changed. Farms spread into the desert and lost their water allocation. Fish hatcheries lost hundreds of thousands of fingerlings when the water became too warm. Cities sprawled, and mandatory low-flow showerheads and water-saving toilets became so common that water districts no longer offer rebates. Now, water districts pay us to remove lawns and we have to remind ourselves that it is OK to irrigate our gardens at all.
And we should water, wisely and efficiently. The new aesthetic takes its cues from the summer-dry climate but that does not mean no summer watering. Our gardens are too important to be left alone, especially in their early years. We need to keep them healthy. Not only do they offer sanity to those of us who would go crazy without them, they provide habitat for critters, keep the soil alive, clear the air, and provide beauty. The new summer-dry aesthetic is rapidly evolving with increased awareness of our limited water resources and all the wonderful new plants and creative ways to use them—but water is critical.
I hope this new aesthetic, which Sean Hogan defines as a climate where grass turns green in winter and brown in summer, is recognized for its own merits. I am convinced it will. Too many people are recognizing the beauty of the summer-dry climate, and too many nursery professionals are bringing us exciting plants for this new aesthetic to go back to wasting water. A little water goes a long way with climate-tolerant plants.
Low-water, not no-water gardens
Climate tolerant does not mean no summer water. Gardens do not occur without our help and in the developed area where we live, plants need to overcome compacted soils, heat sinks of roads and buildings, and the lowering water table as groundwater becomes depleted and drought persists. Gardens deserve some of the water we collectively store as a society, and we need to use
it wisely for the public good. Nevin Smith would let every person guiltlessly have a specified fair share to use however they wanted—to garden, take long showers, or wash their cars. Determining that fair share for personal use is a political hot potato, with farmers, fish, and industry all expecting their share. But gardens are important too.
We need to use what Bart O’Brien calls informed irrigation. Randy Baldwin of San Marcos Growers sees a time when we will use soil probes to decide when to water; soil and microclimates vary so much there is no formula for scheduled irrigation. Jeff Rosendale of Sierra Azul Nursery likes the term xeriscape, and recommends customers think of garden plants in terms of water efficiency. But xeriscaping is gardening by water zones—not zero watering. Most plants from summer-dry regions often look better with some summer water. In fire-prone areas, keeping the garden watered keeps the neighbors happy too.
In this creative time of learning which plants are sustainable with whatever amount of water we have, in whatever part of the region we garden, we also need to learn which plants, such as Fremontodendron, will die if water is added to the hot, dry soil they need, or which plants, like Chilopsis, will rot if winters are too cool and wet.