Water wisely: Trees, shrubs in Placer County need deeper, smarter irrigation

Whether you live in the higher elevation of Colfax or the lower foothills of Lincoln and Auburn, chances are your trees and shrubs are thirstier – or wetter – than they should be. In Placer County, which spans USDA Plant Hardiness Zones 6 through 9b, climate conditions vary, but one principle holds true: Deep, infrequent watering is the most effective and sustainable way to keep your landscape healthy. How we water matters as drought cycles become more frequent and water rates rise. Most homeowners overwater, underwater or irrigate in ways that barely penetrate the root zone. The result? Wasted water, unhealthy plants and preventable stress on trees and shrubs that can lead to pest infestations or even early death. According to UC Agriculture and Natural Resources (UCANR), water applied too shallowly evaporates quickly and encourages weak, surface-level roots. On the flip side, too much water, especially near the trunk, can suffocate roots and promote disease. With proper techniques, gardeners can reduce their outdoor water use by 30 to 60 percent – a savings that's good for the environment and your water bill. Why deep watering works Trees – especially mature ones – have root systems that extend 12 to 36 inches deep and can spread well beyond the canopy. Frequent, shallow watering encourages roots to stay near the surface, making plants more vulnerable to heat, wind and drought. Instead, aim to water deeply but less often, encouraging roots to grow downward where the soil stays moist longer. For young trees, use a watering basin or slow-drip system and gradually move the watering zone outward as the tree grows. For established trees, target the outer edge of the canopy, not the trunk, where most absorbing roots live. How much and how often? There's no one-size-fits-all answer, but a good rule of thumb is to apply enough water to moisten the soil 12-18 inches deep, with mature trees even deeper, then let it dry out slightly before watering again. Use a screwdriver or soil probe to test soil moisture and adjust accordingly. In hotter Zone 9a and 9b areas like Auburn or Roseville, mature trees may need deep watering once every two to four weeks in summer, while trees in cooler, higher elevations may need less-frequent watering. If trees are obviously wilting, they need irrigation. Avoid watering in the heat of the day. Early morning is ideal, allowing water to soak in before evaporation increases. And remember: newly planted trees need more frequent watering their first two years, especially during dry spells. The role of mulch and smart design Mulch is your best friend. A three- or four-inch layer of organic mulch, like wood chips or bark, helps retain soil moisture, regulate temperature and reduce weeds. Just keep mulch several inches away from the trunk to prevent rot. Grouping plants with similar water needs – a method known as hydrozoning – also boosts efficiency. Shrubs and perennials that thrive on less water shouldn't be on the same irrigation line as thirsty edibles or new plantings. Signs of over- or under-watering Leaves turning yellow and dropping prematurely? It might not be pests, it could be water stress. Under-watered plants often have dry, crispy edges or drooping leaves, while overwatered plants may have mushy roots or fungal growth. A sustainable garden starts with informed watering. By adjusting your habits, you can save water, improve plant health and keep your landscape thriving – no matter where you live in Placer County. UC ANR is an equal-opportunity provider and employer. The UC Master Gardener mission is to extend research-based knowledge on home horticulture, pest management and sustainable landscape practices to residents of California.