This year, Oregon gardeners have seen a shift from the state’s traditional Mediterranean climate. Extreme weather conditions, ranging from an ice and windstorm to a record-breaking heatwave, have wreaked havoc on landscapes and gardens.
As the climate continues to shift, there are strategies gardeners can implement to better adapt, protect and prepare their plants for other extreme, incoming circumstances.
“There’s great evidence that climate change is occurring and affecting things here in Oregon on a broad scale, and it includes, specifically, higher and higher likelihood of extreme weather events. And we’ve seen some examples of that recently,” said Weston Miller, community and urban horticulturist for Oregon State University Extension Service and Multnomah County Master Gardener Program manager.
Miller will address such events and their consequences in “Adapting Your Garden and Landscape for Climate Change,” a virtual class on Tuesday, Oct. 12. (Register here for the free event.) The presentation is part of the Growing Oregon Gardeners: Level Up Series through the OSU Extension Service Master Gardener Program.
Historically, the climate west of the Cascades consists of moist, cool winters and hot, dry summers, Miller said. While drought happens seasonally and is to be expected, he said springs and summers have been drier and snow is melting faster.
Oregon is “leaning towards regional scale drought that you’re starting to see in California already,” he said.
Greg Shepherd, co-owner of Xera Plants in Portland, said that Oregon’s climate is changing faster than a lot of people have been adapting to with their landscapes.
“A lot of plants you would consider to be a great plant for full sun and dry in Portland, the flowering currant for example, they were really fried and damaged,” he said as he assessed the past summer. “It’s just something that’s happening so fast, a lot of people in the industry and gardeners are going to be struggling to keep up with what to do next.”
What we know about native plants is changing
Looking at native plants and climate change over the past 50,000 years, Shepherd said that many native plants have migrated as the climate slowly changed. The problem now is that weather and precipitation patterns are changing faster than the plants can migrate.
An “important thing with native plants for gardeners is helping them adapt and preserve the populations until they have a chance to migrate to where they’ll have to go in the future,” he said.
When so many native plants were damaged during last summer’s heat dome, Paul Bonine co-owner of Xera Plants said that it was a “big shock to everyone that the native plants would have reacted that way.” As a result, customers were starting to rethink their landscapes.
“People are sick of watering,” Bonine said. “It’s expensive and they want their landscapes to succeed, so they’re taking out a lot of high-water plants and replacing them with plants that can get along with natural rainfall.”
Shepherd said that every day a customer will come to Xera Plants looking for lower water use plants. Although he said the answer “isn’t 100% clear yet,” people are looking for traits like heat tolerance and drought resistance.
With the nursery’s focus on growing naturally climate-adapted and West Coast native plants, Shepherd said they are looking at their product line and evaluating what they will continue to grow and how they will expand their offerings.
“There’s some interesting things out there that we haven’t relied on, and this is starting to look like a new reality. People are going to want to experiment with things they know will work,” he said.
Miller said he recommends people take a longer view of their landscape and consider the potential impact of extended drought and water restrictions that might be put in place.
“I’d say people who are either re-landscaping or replacing plants, that they consider picking drought-tolerant plants in the first place,” he said. “Drought-tolerant plants are able to survive and bloom normally after an establishment period, and still look pretty good even without supplemental water.”
Bonine adds that gardeners also shouldn’t be afraid to try new things in their landscapes.
“You have a lot more options than you think to get the aesthetics that you want and still have it be low-water,” he said.
Shepherd added that it also doesn’t have to be all cactuses: “You can actually have a lush looking garden that doesn’t require any use of water if you plan your plants carefully.”
Bonine said that after this year’s extreme weather, gardeners will need to focus on resilience in the future.
“The least understood part about gardening is the climate,” he said. “The climate is going to be changing really fast, faster than people anticipate and so we’re just going to play it by ear mostly and see what happens.”
8 steps gardeners can take to help plants and trees adapt to climate changes
Prepare the soil. When planting, dig down deeply enough (a foot down for a 5-gallon shrub, for instance) and work in compost so the roots have something to grow into. “When roots have better established root systems, they are better able to extract water,” Miller said. “If people just dig a hole in their hard, compact clay soil without really preparing a larger planting area, plants are always going to suffer because the roots are shorted by the compacted soil.”
Consider plant location carefully. Some garden favorites, like hydrangeas, rhododendrons and azaleas prefer shade Miller said, and if they are planted in full sun they will be under more stress. Often, plants will show signs of extreme heat when located on the southwest side of a property or in an area facing a patch of asphalt or concrete. Gardeners can also pick more heat-tolerant species of their water-loving plants such as hydrangeas that can better ride out heat waves. Oak leaf and smooth hydrangeas are two species to consider.
Garden in zones. Shepherd suggests gardening in zones by grouping together high-water and low-water plants. He said it’s more efficient and helps constrict water use.
“So, say you want more water intensive perennials, you group them near the hose instead of putting them out,” he said. “Having perimeters of your house be low-water will make maintenance a lot easier.”
Watch for freezing patterns in winter. Miller said with the unpredictability of climate change, it’s not just finding plants that are drought tolerant, but cold hardy as well. “It might be really warm all the way up to Thanksgiving and then it gets really cold the next week and the plants haven’t really acclimatized,” he said, adding that gardeners should learn to recognize the signs of cold damage and take a wait-and-see approach. “In six months, you can see if something is dead or not and then prune out dead stems at that time.”
Look at drought-tolerant native plants: Shepherd recommended manzanita, a West Coast native that is dry adapted and doesn’t like water in the summer, as well as other native annuals that don’t need summer irrigation and support local pollinators, such as clarkia, madia and gilia. Another good option is the serpentine sunflower, a Southern Oregon native that seeds itself and doesn’t require much summer water. He also recommended bulbed plants such as the harvest lily. “Whether native or non-native, (bulbed plants) are acclimated to summer drought,” Shepherd said. “So they’re a good thing to plant for that seasonal flowering without the support that comes with a lot of summer perennials.”
Think Mediterranean for drought-tolerant plants. Miller said to pick plants from lower Mediterranean like climates, where herbs such as lavender, rosemary and thyme thrive. Other recommended plant origins include South Africa, south Australia and Chile. “Plants from those origins also are accustomed to that wet winter and summer drought scenario,” he said.
Deep watering. For trees like conifers and Western red cedar that are experiencing drought stress, Miller’s main recommendation is to water deeply every two weeks (during the dry season) to keep trees healthy. One side effect that Miller has seen in stressed trees is insect attraction and damage, problems that can be prevented by keeping trees healthy through deep watering.
Prune branches selectively. For both conifers and deciduous trees, Miller suggested removing branches that are damaged or pruning to counteract the sail effect (wind drag), where a trees’ foliage gets caught in the wind and weighs the tree down. That pruning can help minimize damage in case of an ice or wind storm, he said. He also recommended coming up with a pruning plan with an arborist.
Consult an arborist. When it comes to trees, Miller said the first two things people should consider are fire danger — particularly those at the urban-rural interface — and how a wind or ice storm would impact the property. “I would probably think about proactively having an arborist come to one’s property and check out several things,” Miller said, adding that this is a process that takes place over years and requires building a trusted relationship. “Trees seem like a great idea on an urban property but they’re expensive to deal with,” he said.
— Aliya Hall, for The Oregonian/OregonLive
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