Plants for a Thirsty State by Nevin Smith and Ginny Hunt © 2016 Suncrest Nurseries, Inc. www.suncrestnurseries.com Introduction As we approach the close of a fourth critically dry season in California, it is time for those of us who love to garden to take stock of where we've been, and where we're going. It is probably safe to say that the days of extravagant water use are over, except perhaps in the wettest years. But a constructive challenge remains: How to continue to provide beauty and diversity in the garden with a more limited water budget. You may wonder whether there is really a good variety of water-conserving plants to choose from, in terms of forms, textures and colors, and whether they can be grown by ordinary mortals. This booklet is devoted to answering these questions with an emphatic "Yes". "Drought Tolerance" and the Real World Few phrases have been so much used and abused concerning garden plants in the past four years as "drought tolerant". The concept is well-intentioned, but it means radically different things to different people, including professional horticulturists. It can cover desert plants, like the agaves, that can thrive for months or years with no water beyond meager winter rains. It is more often applied to plants that will live, sometimes thrive, with natural winter rainfall in more temperate regions and irrigation every few weeks in the summer. And sometimes it is altogether misapplied, to plants that simply don't consume as much water as others for growth and maintenance, though they should never go dry. You will see only a few uses of "drought tolerant" in the descriptions included in this booklet, and many like "moderate to occasional watering", that state a range of plant tolerances. This still leaves ample room for confusion, so let us try to explain our terms a bit. What It All Means Interpreting instructions like "occasional watering" can be maddening for anyone who is new to gardening. The key to its understanding is that it’s all relative, and that the actual regimen needs to be worked out over time by observing garden plants. Watering needs are related to stress factors in the environment itself. Frequent summer fog near the coast reduces loss of water from plant leaves, and both low humidity and high heat in interior valleys dramatically increase it. However, heavy (denser and higher-clay) soils in those same valleys can also retain water longer between irrigations, while sandy soils lose it faster. Short of actual wilting, plants show drought stress through slower growth and, in extreme cases, premature yellowing and loss of older leaves and finally shriveling of new shoot tips. Large excesses of water promote fungus pathogens that actually kill plant roots. This is often reflected in a yellowing of most or all foliage and, as plants near death, wilting of the leaves without actually drying. Where a range of treatment is shown, as (quite often in the descriptions below) "moderate to occasional watering", what is implied is simply a broad range of tolerances. Often, when a little more water is available, plants will look better, grow more strongly and flower more heavily over a longer season; however, the minimum shown will keep them in healthy condition and not create too much stress. There are also (usually) major differences between the irrigation requirements of established trees and shrubs (less frequent) and more shallowly rooted perennials (more frequent). "Moderate watering", for the coastal gardener, might mean a careful, deep irrigation every ten days to two weeks during the summer and fall, until natural rains begin, and at least monthly irrigations in the same manner during long midwinter and spring droughts. For the interior gardener, it might mean weekly irrigations during mild periods, and watering twice a week during heat waves. "Occasional watering" might mean once every three to four weeks for the coastal gardener as applied to flowering perennials, even less during long foggy periods, or for well-established trees and shrubs. Central Valley gardeners should interpret it as meaning once every two or three weeks for the perennials, and every three to four weeks for trees and shrubs. The level of underground water tables will also impact irrigation requirements for deeper-rooted plants in all regions. Finally, where you see the occasional reference to "little watering" or "drought tolerant", applied both to true dryland plants and summer-dormant perennials and bulbs, deep watering once or twice in a summer should suit their needs, especially if the ground is dressed with a mulch of some kind (this both reduces soils temperatures by shading and retards evaporation). A critical element in all of these estimates is how plants are watered. Whether by slow soaking by low-volume i watering heads or by the filling of summer basins (which are knocked down in winter to minimize flooding of roots), plants should be watered deeply enough to reach most of the root system with each irrigation. If you have doubts, dig beside a sample plant an hour or two after watering, and check the depth of soil moisture. Deep watering encourages roots to reach lower soil zones that are more likely to hold and retain water. Finally, almost any plant from a nursery container will require more frequent watering during its first (sometimes even second) summer than in succeeding years. One tried and proven way to speed root development and minimize the establishment period is to plant in fall, when normal rains (usually) begin. Exposure Many of the plants described here actually need full sun at least part of each day for strong growth and flowering. In other cases, their needs will depend on where you garden. A common line in the descriptions that follow is something like, "Sun or light shade near the coast, part shade inland". This reflects the fact that generally cooler air and soil temperatures near the coast reduce plant stress, including the loss of water and actual burning of leaves. On the other hand, the only way to maintain some plants (for example, high mountain natives) in consistently hot-summer areas is to shade them a bit during the heat of the afternoon—for example, by planting them under trees. Soils Those of us who live near the coast may naturally enjoy what are described as "well-drained soils". We often live on ancient dunes and coastal terraces where any organic matter is well mixed with sand or gravel, and water percolates well down through the network of plant roots, leaving both moisture and a good bit of air behind (plant roots breathe, too). People who live in valley bottoms and the flood plains of present or former rivers may have much denser soils, with high clay content that impedes both air circulation and the drainage of water through the root zone. In this case, where "well-drained soils" are recommended, one may have to take one or several measures to improve drainage: Build raised mounds or berms on which to plant; add bark or other organic amendments to open larger spaces between soil particles; possibly add coarse sand and gravel to the resulting mix for the touchiest plants (often those from mountain slopes). The soil portion of each description that follows will at least give you a starting point, and your own eyes, digging arms and observation of what happens when you water should provide the rest. Hardiness There are many ways to state an estimate of winter hardiness for a given plant: USDA zones, now used around the world, and the much more elaborate Sunset zones, that account for both winter cold and summer heat and humidity, are a couple. We have chosen to use conservative estimates of the lowest temperature, in degrees Fahrenheit, that a plant will endure for short bouts in the winter and fully recover from in spring. That said, there are some cautions that we have experienced in the most painful way at the nursery: Especially near the coast, mild temperatures may continue late into the fall (sometimes even early December), encouraging plants to continue soft, summer-like growth. Then comes a sudden winter blast, with temperatures falling within a few days into the 20s or even the teens. Even the hardiest plants (for example deciduous shrubs from northern climates) may be heavily damaged under this scenario. On the other hand, a more gradual descent in night temperatures encourages even tender plants to bring growth to a halt, develop sturdier tissues, and be better prepared for the ultimate winter freeze. We hope that you'll enjoy using the plant guide that follows, and find it valuable both in selecting plants for your "unthirsty" garden and in keeping them beautiful. ii Plants for a Thirsty State ABUTILON palmeri. Indian mallow. Indian mallow hails from our southern deserts. It is quite distinct from the hybrid abutilons, growing about 3 feet high and broad. Both the stems and large three lobed leaves are densely covered with white wool, giving it a striking, almost ghostly appearance. From mid spring to late fall, in mild climates, it produces a continual succession of golden yellow to bright orange (not the usual tawny shades) flowers, each about 1.5 inches broad, on wand-like stalks. This is an interesting novelty shrub for gardens in mild climates. It is best planted in well- drained soil, in a sunny spot. Occasional watering. Hardy to 20-25 degrees F. ACACIA. Wattle. Widespread. A vast genus of trees and shrubs from many habitats, often with attractive divided leaves. Flowers are tiny but often borne in dense clusters.