Q: In several publications, the term “water-wise” is used along with “drought tolerant” to describe some natives. During a hot Pacific Northwest summer, would this mean watering once a week or more frequently? Some plants, such as the red currant, don’t want watering (or only little) during the summer months, but I’m worried about not watering at all. I’m putting in a drip irrigation system and am trying to work out schedules and how much to give which plants. For non-natives that like the Mediterranean climate, such as lavender and rosemary, would the same watering schedule apply?
A: This issue encompasses three areas: plant choice (what), plant environment (where), and watering techniques (how).
The use of native plants in the landscape means that those plants have, over thousands of years, become accustomed to our region’s soils, water supplies and temperatures. The current challenge, in light of climate change, is to observe which species will be able to adapt to less water and higher temperatures. Non-native plants, such as lavender, which are native to Mediterranean areas and are not invasive, can be incorporated into the landscape without a risk to the native plants that can adapt. You can go the entire summer and never water lavender and rosemary once they are established in the soil, which typically takes a year.
The second consideration is where you plant these species. Assuming the plant is not a flowering one (which typically requires some hours of direct sunlight), situating your plants in shade or part-shade means they are in soil that will stay cool and moist longer, an environment that requires less supplemental watering. Those areas will not be on the same schedule needed for plants in full-sun, well-draining, hot spaces.
The third part of the equation is to measure whether the plant roots are already surrounded by enough water to prevent them from drying out. This can be accomplished by using an inexpensive water meter, which works much like a thermometer, and can tell you the amount of moisture in the soil. Some prior knowledge of the plant is helpful so you can pair species with similar water (and sunlight) needs, preventing water waste.
Your drip system might be superfluous for many species — there’s no reason to place plants near it if it’s not necessary. When you water — preferably when it’s cooler so there is less evaporation — and how you water — in-ground and soaker being the least wasteful — will have a long-term impact on your environment specifically, and the region’s water scarcity issues overall.
You can find more specifics about species selection and water in the WSU publication “Watering Home Gardens and Landscape Plants.”
— Kris LaMar, OSU Extension master gardener
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