GardenGuy: A New Year and a Change in the Air

A frozen Ronald Bog
photo by Martin DeGrazia

A quick prologue to readers: Yes, this month’s column is, more than anything else, about climate change, aka Global Warming. To forestall the time some readers will feel they need to take to email me and note the ‘overly brisk’ temperatures we recently experienced versus the concept of a warmer winter, do realize that there is a difference between the meteorological terms of ‘climate’ and ‘weather.’ 

The very short answer for those 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’s the weather like today or next month and what’s discussed during the 6:00pm Evening News’ weather segment. 

‘Climate’ describes what that weekly weather is like (as described by some 11,000+ weather stations across the country) over the long-term, generally thirty years or more. What are the averages of precipitation, temperature, sunshine, etc. in a particular area? At the moment, there’s a chill in the air, however, long-term………. Now, on to the actual article.

Happy New Year all! And, welcome to yet another year of the fun and challenges in the Pacific Northwest world of gardening. I’m still trying to decipher the post-Christmas instructions and ramifications for one of our newest presents from the federal government; the report about our part of the state now categorized as being in USDA Hardiness Zone 9a (!). 

My, how we have grown! I can remember back to the early 1980’s when I moved to Seattle and was in Zone 7b (average winter low between 5° and 10 degrees) and, in 2012, was raised to Zone 8b (an average low of between 15 and 20 degrees). How quickly they grow! 

So, what are the ramifications of this climatic news? What does it mean in our roles as home gardeners who may hold all horticultural titles on our respective pieces of earth as designer, landscape maintainer, pest controller, etc. The thirty-year warming trend, which meteorologists talk about during the evening news, continues as the related heat and horticulture issues, increasingly, evolve around us. Let’s take some time to consider where gardeners need to be more aware, more proactive. 

 Let’s start by looking at our current winter weather.

Across the continental USA, the lowest average winter temperature is predicted to be 2.5 degrees (Fahrenheit) warmer than when the last map was published some ten years ago. Winter and nighttime temperatures are rising faster than summer and daytime temperatures. Now, 2.5 degrees might not seem a great deal warmer in ten years, but, the effect has been cumulative over the past century, over the last thirty years and, certainly, over the past three record-breaking years. 

The trend is clear: Earth is warming because of our increasing populations and longstanding reliance on fossil fuels. According to the federal government's latest National Climate Assessment, as our cars, buildings, industries and power plants continue to burn more fossil fuels and emit greenhouse gases, the planet will continue to warm. By 2050, Seattle is expected to average around 27 days per year over 85 degrees and an increasing frequency of heat waves. Start buying your supply of sunblock protection and wide brimmed hats now!

Bronze birch borer

The Pacific Northwest is already experiencing climate change (have you been here for the past few summers?) which will become even more evident in the decades ahead. 

With warmer minimum temperatures, certain insects that would usually die in winter will be able to survive year-round and multiply in greater numbers. 

And, as maximum temperatures rise in the summer, heat-stressed plants can become prime targets for destructive pests such as the bronze birch borer (pictured left) and western pine beetle. 

A warmer climate will also provide a better environment for mosquitoes, ticks and fleas. Remember that Western Washington had its first case of West Nile Virus just last year. Look for more glaciers and polar ice caps to melt at faster rates, sea levels to rise and weather-related disasters like wildfires and floods to become more common. 

The warmer winter temperatures will also cause precipitation in the Cascades to fall as rain rather than creating the usual snowpack that slowly melts throughout the summer and keeps our region hydrated and green. Certainly, these changes won't happen overnight. You might not notice them every day, every month or even every year. But they are happening. We still may have time to shape our future, for better or for worse. A profit of doom, I’m not. However, the climate is what it is or what we help it to become.

Rock rose

Take a look at Washington’s state plant, the rhododendron. Did you notice some of their leaves drooping and turning brown around the edges these past few summers? 

How about our Acer macrophyllum (Large Leaf Maples) many of whose leaves have been shrinking in size for the past few years or the Tsuga heterophylla (Western Hemlock) that are experiencing brown-out along their branches, all due to the increasingly hotter and drier summers? 

It may be time to think about landscape ‘editing’ which includes more native plants, but native to Zone 9. Plants like Cistus (Rock Rose – pictured right), Chamaecyparis (False Cypress), Pinus ponderosa (Ponderosa Pine) and similar warmer zoned plants may be good candidates to fill the garden spaces of their heat-stressed predecessors. Also, start tracking the timing between when your current plants begin to flower earlier in the season and when their feeding pollinators are around. It’s one more cue to determine zone hardier plants and their fitness for changing landscapes.

Mentioning ‘pollinators’ raises another gardener’s issue: new insects and new diseases will become more common to challenge your fortitude and outdoor ingenuity. Watch for the scourge of roses, Japanese Beetles. They haven’t made it all the way from the east coast to western Washington as yet, but, they are closing-in with recent sightings in eastern Washington and south of Portland, OR. Also, watch for larger populations of the brown marmorated stink bugs to disturb your horticultural zen and bronze birch borers attempting to take down your White Himalayan Birch from the inside.

Against these prognosticated weather changes, can gardeners do anything to lessen the intensity of the problem? 

The task may seem akin to one person removing a cup of water from the ocean and expecting to see the water level fall a bit. Unfortunately, it will take more effort than that. It will take a concerted, global effort. 

In response to this challenge, as part of the individual efforts in your own yards, there are plenty of eco-friendly, cost-saving design tasks you can consider to help Seattle, the State and, of course, the world (not a bad result from all of us making simple changes to our landscapes. 

Adding more drought-tolerant plants to the landscape and switching from gas-powered lawn mowers and weed whackers are the first actions that come to mind. How about removing some or even all of that front lawn and adding water-efficient perennials, shrubs, etc.? I’m anticipating having an article and, perhaps, a gardening talk on the topic later this year. Let me know if you are interested in attending such a program.

New growing possibilities for the edible garden

On the positive side of the coin, the revised plant hardiness map may present new growing possibilities for the region’s gardeners, such as winegrape growing in Puget Sound. 

Edible gardens could experience improved harvests of eggplant, melons and other hot weather vegetables. New varieties of flowers may do better than they have any right to in the warmer weather. 

While warmer temperatures are projected to shorten the snow season by half in portions of the Cascades, thus cutting into winter sports, there is also the chance the change might expand access for activities like hiking and camping. 

The demand for warm-weather activities like cycling and boating might also increase. Things are going to change. There are going to be winners and losers in the region’s landscapes. As gardeners, we need to be pro-active and willing to change the way ‘things have always been done.”

When you use plants appropriate for your growing zone, it is not an absolute guarantee that they will be successful, but it is an excellent place to start. Experienced gardeners know there are other factors at play when deciding on which plants to use, including soil type, humidity and the effect of microclimates. 

Start with plants that are recommended for our changing hardiness zones, then research other factors that may have an influence on your plants as well. Local nurseries and garden centers carry native species that are suitable for our changing regions. 

In addition to choosing the right plants which will survive both our winters and summers, be sure to check and follow the planting and care instructions to ensure a healthy garden. Use some of this winter’s wet days to do the research needed to replace longtime familiar but suffering plants and be willing to try new candidates which will make life easier on your parcel of land in this green paradise called the great Pacific Northwest. 

Happy Gardening all!

Further Reading:

Crimmins, A.R., et. al. (eds.) 2023. Fifth U.S. National Climate Assessment Federal Report. U.S. Global Change Research Program. Washington, DC. https://doi.org/10.7930/NCA5.2023.CH1

Dalton, M.M., et. al. (eds). 2013. Climate Change in the Northwest: Implications for our Landscapes, Waters 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 columnist, Bruce Bennett, is a WSU Master Gardener, garden designer and lecturer. 

If you have questions concerning this article, have a gardening question or two to ask concerning your own landscape or want to suggest a topic for a future column, contact him at gardenguy4u@gmail.com.

See Bruce's previous columns here