Meet Horticulturist Christina Pfeiffer, author of  “Pacific Northwest Month-By-Month Gardening”. She gardens in Seattle, Washington, Zone 8. In this profile, Christina shares her expertise in planting and maintaining gardens that are sustainable in our changing climate. You can learn more about Christina and her lectures at her website. 

What is the most important thing people can do in their garden to mitigate the impacts of climate change?

Take really good care of the soil. Minimize soil disturbance. Use coarse textured organic mulch that will promote both water infiltration and retention, and that will support soil building organisms. For gardens that require summer irrigation, water deeply and infrequently. These tactics will foster greater rooting depth, which serves to improve the vigor and resilience of all kinds of garden plants.

Arthur Menzies Mahonia. Photo credit Christina Pfeiffer.

How is climate change affecting my gardening practices?

I am more thoughtful about how gardening practices can impose or reduce overall plant stress and try to minimize overall disturbance. Many of my usual “garden with the season” benchmarks have been shifting, making it even more important to pay attention to current and recent weather patterns in relationship to the timing and methods of garden care. I lean toward greater moderation when pruning garden trees and shrubs. I prioritize maintaining tree health over smaller garden plants and I’m learning to accept that the same patch of earth may not be able to support the same group of plants as in years past.

A shade cover to protect transplanted plants from the sun and heat. Photo credit Christina Pfeiffer.

What are some of my favorite resources for creating resilient gardens?

I offer a quarterly Zoom series, “Gardening with the Seasons” as part of the University of Washington Botanic Gardens Public Education Program.  Each session highlights information from the Pacific Northwest Gardening Month-by-Month book, tailored to the specific conditions of the current gardening year.

The Conscientious Gardener: Cultivating a Garden Ethic is a great book by Sarah Hayden Reichard, 2011, University of California Press. Dr. Reichard was well attuned to the coming impacts of a warming climate when this book was written, and it remains a great primer on the science and practical aspects of gardening in the context of a changing environment.

To learn more about soil health, visit the USDA Natural Resources Conservation Service Soil Health.

Christina offers many classes on pruning for optimal plant health. Photo credit Christina Pfeiffer.

What are some common PNW plants that may not be well suited to our changing climate in the future?

The first that comes to mind are birch trees, which are on the decline due more to warmer seasons than to bronze birch borers. Drought stressed trees are most susceptible. The first time I observed bronze birch borer in Seattle was in 2015. At the time, I thought the infestation was related to a sudden lack of irrigation at that site. I now realize it was more likely an early symptom of extended years with warmer growing seasons than birches tolerate. These trees are native to regions with summer rain and they prefer more moderate summer temperatures. It is becoming more difficult to grow healthy birch trees in our region, even in irrigated gardens. So far, river birch has been less susceptible (provided it is grown on moist sites!). Many sheared Fraser’s photinia have displayed increased leaf spot diseases, decline, and death over this same period, while specimens grown to natural form have stayed healthier. I attribute this difference to the stress imposed by shearing, in combination with longer, warmer, and dryer growing seasons.

With changing weather patterns, what is the best time to plant in the PNW?

Planting during the cool seasons is optimal to give roots a jump-start on establishing new growth before the first growing season. Trees, shrubs, and many herbaceous plants installed during milder periods in the fall through March generally establish with less transplant stress and less irrigation than those planted in late spring or summer. When planting outside of the dormant season, target cooler and overcast days for planting, or at the very least, plant later in the day so plants can recover overnight, and water diligently for the first weeks. In addition to the timing, proper root ball preparation and not planting too deep will make a huge difference in long term plant performance and resiliency.

Plant in the fall during cooler weather for best results. Photo credit Christina Pfeiffer.

Thank you, Christina, for sharing so many great tips!