There is no shortage of alarming news about our planet’s changing climate. As gardeners, we feel these changes. After all, we work in the trenches. Here in the Pacific Northwest, changing precipitation patterns are of immediate consequence.
The University of Washington Climate Impact Group, the U.S. Geological Survey, and the U.S. Forest Service collaborated on studies that are cited in an article on the U.S. Fish & Wildlife website. The article, titled “Climate Change in the Pacific Region” outlines the impact of temperature and precipitation changes, and predicts how future changes will affect wildlife, forests, and coastal and marine environments.
From my own unscientific observations, I have seen an increase in intense rainstorms from late autumn through winter, followed by a decrease in summer rainfall and humidity. This pattern takes a toll on plants that can’t adapt quickly to such extremes. The damage from these changes is distinctly seen in early leaf-drop and stem dieback, most noticeably in native plant populations. For example, the public garden I maintain in Seattle’s Carkeek Park is home to a large, mature stand of Corylus cornuta subsp. californica. In the especially dry summer of 2015, these tall, lovely shrubs dropped most of their foliage by mid-July; by the end of August, they were completely bare.
We have since discovered considerable dieback on last year’s growth. My instructions were to not water native plants in this public garden during the drought, and the resulting damage was extensive. Our fern collection, including decades-old stands of Western sword fern (Polystichum munitum) and lady fern (Athyrium filix-femina) have suffered considerable die-off as well.
How do these changes in our local climate affect the home gardener? Arguably, the most immediate impact is an increase in our summer water bill. Even with the help of rain barrels and mulch, when high heat and low humidity extend for weeks, watering becomes a concern. Here are some ideas that will help your Pacific Northwest garden survive summer with less damage, while minimizing extra work and large water bills.
Water-loving shrubs, perennials, ferns, and grasses create intriguing and beguiling combinations. My garden contains hydrangeas, hostas, blue-eyed Mary (Omphalodes verna), Enkianthus campanulatus, golden Japanese forest grass (Hakonechloa macra ‘Aureola’), Amsonia, and a variety of ferns, all of which appreciate even moisture. By grouping these plants together in a bed containing rich, loamy soil that retains moisture, I can enjoy their presence in the garden and efficiently attend to their watering needs. With a deep layer of mulch I only have to water every three to four weeks during summer.
Building good soil produces results that far exceed the amount of work required. Of all the beneficial practices home gardeners can employ to help gardens withstand periods of seasonal drought, this is the most important. Fertile, healthy soil produces plants that are more resistant to disease and insect infestation as well as the vagaries of weather. Just a few steps will start your garden soil on the path to long-term health:
• Apply compost in spring and autumn, or check with your local county extension office for their recommendation.
• Leave fallen disease-free plant material on the soil surface—you can cover the debris with a light layer of mulch for a tidy appearance, if you want.
• If the lawn has not been treated with chemicals, lawn clippings may be added to beds.
• Keep soil mulched year-round.
I’ve followed these soil-building practices for years, and now I only fertilize container plantings; my plants are healthy and disease free, and our landscape supports a large number of pollinators, beneficial insects, and a diverse bird population.
Watering deeply but less often, ideally using soaker hoses or a drip system encourages plants to develop an extensive root system, which in turn enables them to survive periods of drought. This approach also cuts down on evaporation, as more water is stored in the soil than is lost with shallow, frequent watering. Avoid watering in the heat of the day to decrease evaporation. Again, a layer of mulch helps to retain soil moisture.
These days, a large portion of my landscape is devoted to plants that will survive summer without supplemental water. A wide variety of drought-tolerant plants adapted to xeric conditions grow successfully in the Pacific Northwest. Plants I grow in these dry areas include Yucca filamentosa ‘Golden Sword’, a variety of sedums, Caryopteris ×clandonensis ‘White Surprise’, lavender, rosemary, Epilobium canum (syn. Zauschneria californica), Helianthemum nummularium, and many others. One of my favorite drought-tolerant plants with a large, dramatic presence is Grevillea victoriae; gray foliage and beautiful orange blooms in winter make this plant a focal point in the garden. These plantings receive no water other than rain.
As the climate continues to change, every region will continue to experience shifting weather patterns—longer droughts, warmer winter and spring temperatures, greater seasonal temperature swings, or more flooding followed by landslides and soil erosion. We cannot control the weather. But we do have some control over how our landscape copes with these extremes. By building and maintaining healthy fertile soil, practicing smart watering practices, and grouping plants with similar water needs together, the Pacific Northwest gardener can help their garden favorites adapt and thrive.