EDITOR’S NOTE: “The Garden Guy” is a monthly column written by a WSU Certified Master Gardener that discusses various horticultural topics that local residents may find noteworthy or suggested by you, our readers. Master Gardener and Landscape Architect Bruce Bennett is also available to answer your gardening questions. Look for his column every third Friday of the month.
By Bruce Bennett
WSU Certified Master Gardener
A new year and a change in the air
A quick prologue to readers: Yes, this month's column is about climate change, also known as global warming, more than anything else. To avoid some readers feeling like they need to take the time to email me and note the “overly chilly” temperatures we've been experiencing recently compared to the idea of a warmer winter, they should Be aware that there is a difference between the meteorological terms “climate” and “weather.” The very short answer for these readers is: “Climate is what you expect and weather is what you get.” In other words, “weather” refers to short-term changes in the atmosphere; What is the weather like today or next month and what will be talked about in the weather section of the evening news at 6:00 p.m. “Climate” describes what the weekly weather (as described by more than 11,000 weather stations across the country) is over the long term, generally thirty years or longer. What are the averages for precipitation, temperature, sunshine, etc. in a particular area? There's a chill in the air at the moment. However, in the long term………. Now to the actual article.
Happy New Year everyone! And welcome to another year of fun and challenges in the world of gardening in the Pacific Northwest. I'm still trying to decipher the post-Christmas instructions and implications for one of our newest gifts from the federal government; the report on our part of the state now classified as USDA Hardiness Zone 9a (!). My goodness, how we have grown! I can remember in the early 1980s when I moved to Seattle being in zone 7b (average winter low between 5° and 10 degrees) and in 2012 it moved to zone 8b (average low between 15 and 20 degrees). . How quickly they grow! What impact does this climate news have? What does this mean for our role as home gardeners who can hold all the horticultural titles on our respective piece of earth as designers, landscapers, pest controllers, etc.? The thirty-year warming trend that meteorologists talk about on the evening news continues as associated heat and horticultural problems increasingly unfold around us. Let's take some time and consider where gardeners need to be more mindful and proactive. Let's start with a look at our current winter weather.
Across the continental United States, the lowest average winter temperature is expected to be 2.5 degrees (Fahrenheit) warmer than when the last map was published about a decade ago. Winter and nighttime temperatures are rising faster than summer and daytime temperatures. Now, 2.5 degrees in ten years might not seem like much warmer, but the effect has accumulated over the last century, over the last thirty years, and certainly over the last three record years. The trend is clear: the earth is warming due to our growing population and long-standing dependence on fossil fuels. According to the federal government's latest national climate assessment, the planet will continue to warm as our cars, buildings, industries and power plants continue to burn more fossil fuels and emit greenhouse gases. By 2050, Seattle is expected to have an average of 27 days per year above 85 degrees Celsius and the frequency of heat waves is increasing. Stock up on sunscreen and wide-brimmed hats now!
The Pacific Northwest is already experiencing climate change (have you been here in recent summers?) that will become even more evident in the coming decades. With warmer minimum temperatures, certain insects that would normally die in the winter are able to survive year-round and reproduce in greater numbers. And as summer maximum temperatures rise, heat-stressed plants can become prime targets for destructive pests such as: Bronze birch drill (picture on the left) and Western pine beetle. A warmer climate also provides a better environment for mosquitoes, ticks and fleas. Remember, Western Washington had its first case of West Nile virus just last year. Watch for more glaciers and polar ice caps to melt faster, sea levels to rise, and weather-related disasters like wildfires and floods to occur more frequently. The warmer winter temperatures will also cause precipitation in the Cascades to fall as rain instead of forming the usual snowpack that slowly melts throughout the summer, keeping our region hydrated and green. Certainly these changes will not happen overnight. You may not notice them every day, every month, or even every year. But they happen. We may still have time to shape our future, for better or worse. I am not a profiteer of ruin. However, the climate is what it is or what we help make it become.
Take a look at Washington's state plant, the rhododendron. Have you noticed over the past few summers that some of their leaves are drooping and turning brown at the edges? How about our Acer Macrophyllum (Large-leaf Maple), whose leaves have often become smaller in recent years, or Tsuga Heterophylla (Western Hemlock), whose branches are turning brown due to increasingly hotter and drier temperatures? Summer? It may be time to consider landscaping that incorporates more native plants, but those that are native to Zone 9. Plants such as Cistus (rock rose – pictured left), Chamaecyparis (false cypress), Pinus Ponderosa (ponderosa pine) and similar warmer zone plants could be good candidates to fill the garden spaces of their heat-stressed predecessors. Additionally, start tracking the timing between when your current plants start blooming earlier in the season and when their feeding pollinators are nearby. This is another clue to determining zone-hardy plants and their suitability for changing landscapes.
The mention of “pollinators” raises another problem for gardeners: new insects and new diseases will become more common, testing your outdoor strength and ingenuity. Watch out for the scourge of roses, the Japanese beetle. They haven't quite made it from the East Coast to western Washington yet, but are getting closer with recent sightings in eastern Washington and south of Portland, Oregon. Additionally, keep an eye out for larger populations of brown marmorated stink bugs that could disrupt your gardening and bronze birch borers that may attempt to destroy your Himalayan white birch from the inside.
With these predicted weather changes, is there anything gardeners can do to reduce the intensity of the problem? The task may be similar to a person fetching a cup of water from the sea and expecting the water level to drop slightly. Unfortunately, it will require more effort. A concerted, global effort is needed. In response to this challenge, as part of individual efforts in your own gardens, there are numerous eco-friendly, cost-saving design tasks you can consider to help Seattle, the state, and of course the world (not bad) The first steps we take What comes to mind are adding more drought-tolerant plants to the landscape and switching from gas-powered lawn mowers and weed whackers to the front yard and water-efficiently adding perennials, shrubs, etc.? I expect an article and perhaps a gardening lecture on this topic later this year. Let me know if you would like to participate in such a program.
On the bright side, the revised plant hardiness map may provide new growing opportunities for the region's gardeners, such as growing grapes in Puget Sound. Edible gardens could see better harvests of eggplant, melons and other vegetables in hot weather. New flower varieties may do better in warmer weather than you'd like. While the warmer temperatures are expected to shorten the snow season in parts of the Cascades by half, limiting winter sports, there is also the possibility that the change will expand access for activities such as hiking and camping. Demand for warm-weather activities such as cycling and boating could also increase. Things will change. There will be winners and losers in the region's landscapes. As gardeners, we must be proactive and willing to change the way “things have always been done.”
Using plants that are suitable for your growing area is not an absolute guarantee of success, but it is an excellent starting point. Experienced gardeners know that other factors come into play when deciding which plants to use, including soil type, humidity and the effects of microclimate. Start with plants recommended for our changing hardiness zones and then examine other factors that may also have an impact on your plants. Local nurseries and garden centers stock native species suitable for our changing regions. In addition to choosing the right plants that will survive both our winters and summers, be sure to review and follow planting and care instructions to ensure a healthy garden. Take advantage of some of this winter's wet days to do the research necessary to replace familiar but suffering plants and be ready to try out new candidates that will make life easier on your property in this verdant paradise called the Pacific Northwest.
Have fun gardening!
Further reading:
- Crimmins, AR, et. al. (ed.) 2023. Fifth Federal Report on the U.S. National Climate Assessment. US Global Change Research Program. Washington, D.C https://doi.org/10.7930/NCA5.2023.CH1
- Dalton, M.M., et. al. (Ed.). 2013. Climate Change in the Northwest: Impacts on our Landscapes, Waterways and Communities. Island Press: Washington, DC
- Moore, Darryl. 2023. Gardening in a Changing World: Plants, People and the Climate Crisis. Pimpernel Press Ltd: London, UK.
Contributing garden columnist Bruce Bennett is a Washington State University certified master gardener, lecturer and garden designer in the greater Seattle area. If you have any questions about this article, have a question about your own landscape, or would like to suggest a topic for a future column, contact Bruce at gardenguy4u@gmail.com.