If you recently moved to the southwestern states, you're probably eager to take advantage of our long growing seasons. The American Southwest boasts ample sunlight, warm temperatures, minimal frost, and hardy plants that can cope with the climate. Thankfully, they're hardy enough to withstand trial and error, because many gardeners struggle with watering desert plants. Here are some tips to prevent over- and underwatering:
1. Know your desert. Newcomers may picture our region as a monotonous brown landscape, but this is hardly accurate. You might live in the Sonoran Desert, the Mojave Desert, or the Chihuahuan desert. You might live in an area designated as high desert plains, where prairie grasses grow and snow falls in the winter, or you might be located in the Great Basin areas of Nevada, Utah or Colorado. Select your plant based on your region's climate so that Mother Nature's watering schedule will be more or less suitable.
2. Know your microclimate. You might live in Phoenix, but if your backyard is shady, cool, and prone to puddles, customize your irrigation system accordingly. A south-facing front yard with full sun and natural soil is well suited for cacti, mesquite, and globe mallow. On the same property, you could feasibly grow a vegetable garden in the shaded, mulched and composted backyard. Before planting, always test the soil's drainage to see how fast the ground absorbs water. Low-water plants need fast drainage and moderate water retention. For native plants, the less you amend the soil, the better. Resist the temptation to mulch your barrel cactus, but definitely mulch your roses.
3. Grading. When annual rainfall is scarce, every drop counts, and you might want to direct water to your plants by creating a small basin in the ground. On the other hand, heavy seasonal rainfall (in some cases, even moderate rainfall) can overwhelm some low-water plants. These should be planted on a mound to direct water away from the roots. Observe where city planners have placed different varieties in your area, especially along highways where plants are generally left to fend for themselves. For example, pink fairy dusters grow well on sunny, slightly raised highway medians, so you should plant them in full sun on a slight mound in your garden.
4. Native or imported? I prefer native plants for aesthetic and ecological reasons, but there's something to be said for biodiversity and exotic, noninvasive plants too. Native plant care is fairly intuitive: Does Mother Nature install sprinklers next to her giant saguaro? Neither should you. Leave it alone! However, many popular plants (such as morning glory, sage and marigold) have been adapted to desert climates - some more successfully than others. These ain't your mother's daisies. Trust the care instructions, and ask your nursery specialist for specific watering needs. Remember that "moderate" watering might mean something different in the desert than it does in, say, northern Oregon.
4. Root systems: There are two types of root systems that thrive in a low-water environment. One is a network of shallow roots spread over a large area, which allows the plant to catch scarce rainfall that doesn't really penetrate the soil. The other involves one or more taproots: a deep, thick root that reaches the groundwater supply to take up water even when it hasn't rained for a long time. In general, shallow roots thrive with frequent, short waterings, whereas deep roots prefer periodic, long waterings.
5. Plant morphology: When you see a plant with withered, drooping, dry leaves, it's reasonable to assume that plant is thirsty. Actually, it might be doing just fine. Many plants will fold their leaves and angle them away from the sun during midday to prevent water loss. At night or on overcast days, their leaves will appear more lush. Check your plants at different times of the day before you decide they need water.
6. Signs of overwatering: You're more likely to overwater drought-tolerant plants than to underwater them. As soon as we see signs of stress, our instinct is to pour water on the problem. Besides, overwatering often looks suspiciously like underwatering: brown or yellow leaves, wilting, drooping or loss of leaves. Pests are the surest sign of overwatering, because insects and critters in dry climates are always seeking sources of moisture. They will feast on waterlogged foliage and thank you for your effort. I advise researching your specific plant for troubleshooting tips. In a pinch, check on branches near the leaves and near the plant's base: if they are springy and green on the inside, your plant is well watered.
In general, less is more when watering desert plants. The method and frequency of irrigation depend your plant's needs, and you can save yourself grief in the long run by carefully selecting proper species and planting sites.