Garden Q&A – Irrigation with Natives
CNPS Garden Q&A with Mike Evans, founder of Tree of Life Nursery:
By Mike Evans
Tree of Life Nursery, San Juan Capistrano
What are the most important things to know about watering native plants?
All plants use water on an as needed basis to maintain turgidity (water-filler roots, stems, leaves), to cool themselves (transpiration), and through photosynthesis, to grow. All plants develop adaptations to allow them to thrive in their native regions. For most California natives, this means they possess the ability to survive and grow in an environment that experiences an extended dry period for nearly half the year. The plants do most of their growing during the cool, moist season, and through various adaptations, conserve precious moisture in summer by slowing down transpiration and growth.
Cool Season Watering
During the cool season, native plant gardens require little or no irrigation. During a normal winter season, rain events with sufficient quantity and regularity will provide the needed amount of water for native plants. Irrigation to supplement rainfall will only be needed in dry years, during long dry spells in winter, or on plants that simply require more than normal winter precipitation in a given area.
Warm Season Watering
During the warm season, native plants gardens should be carefully watered to keep them a little tidier than the appearance of their corresponding wild places. This is where the gardener has to be careful. Since natives are using so little water compared to most garden plants, they will not succeed if planted in mixed plantings with other plants that get copious irrigation. The natives will succumb to root rot, because they are not using the water and the roots will be deprived of oxygen in the overwatered soil. Root rot water molds thrive in warm soils that are overly wet. Soils are warm near the surface.
Watering native plants in summer is easy. First, trust the plants to truly be drought tolerant. Next, know that the goal is to promote root systems that grow in cool moist soil, at a depth of 14-20”. You can achieve this by watering thoroughly and infrequently. A good rule of thumb is to apply the equivalent of a rain event totaling 1 to 1 1/2”, about once a month, May through October.
A good way to simulate a monthly rain event in summer is to apply water in the early morning during cool spells. Soak the soil once a day for three consecutive days, for a sprinkler run time of up to 2 hours total. Each 3-day process is considered an irrigation event, and you will only do 5 or 6 of these a year. In between irrigations, you can cool your garden with an occasional light refreshing sprinkle, once or twice a week in the late afternoon. This might mean a sprinkler run time of 5 minutes. You are not watering the soil; you are only wetting the leaves. Irrigation events are more important than refreshing sprinkles. Combined, they will result in beautiful healthy natural gardens.
Much, much more info about watering your native garden is available in our “Watering Native Plants” guide.