OREGON NEWS

OSU horticulturist helps Oregonians fortify lawns, landscapes for climate change

Oregon State University Horticulturist Weston Miller in his Portland garden. Miller stands next to a pineapple guava, a fruiting shrub from South America that can survive in Oregon’s now longer, warmer months. (Alex Baumhardt/Oregon Capital Chronicle)

Weston Miller is helping Oregonians plant for a future of more heavy rains, winds, droughts, fires and bugs. 

Miller directs the West Multnomah Soil & Water Conservation District, is a master gardener and has been a community and urban horticulturist at Oregon State University’s Extension Service for 14 years. 

He teaches people to landscape their properties with plants that are capable of holding more water, staying intact in wind and rain storms and ones that can even protect buildings from fire. 

He said more people in Oregon should begin thinking about climate change when it comes to landscaping they undertake.

“From drought, to algae blooms in freshwater lakes, to freezing rain, wind storms, hot, hot winds, we’re going to expect an increase in the frequency and increase in the magnitude of those kinds of events. So all of that definitely has an impact on people’s properties,” Miller said.

Volunteers at OSU’s Master Gardener Program fielded more than 2,500 questions from the Portland area alone last year, Miller said, including many about planting drought-resistant plants that didn’t need much water. 

This summer, the entire state was in a moderate to exceptional drought, according to the US Drought Monitor. 

Native Oregon plants like rhododendrons and azaleas that are well equipped to survive the region’s Mediterranean climate were scorched and stressed from the heat dome in June when temperatures in parts of the state rose to 118. 

“The evidence about climate change impacting local conditions is pretty clear,” Miller said. 

Iconic Oregon plants and trees stressed

Native Oregon shrubs and trees like Douglas firs and red cedars are stressed by the hotter drier summers and are becoming more susceptible to invasive bugs, fungus and diseases, Miller said. This is happening in both urban and forested areas. 

Bugs that can detect the stress in some plants and trees have proliferated in great numbers, like the lace bug. It detects a specific compound azaleas and rhododendrons release when they’re stressed and weak. The lace bugs attach themselves to those plants and feed on the underside of their leaves. 

Because insect metabolism is based on external temperatures, “if things are a little bit warmer, then we’re going to see the insect life cycles with an additional generation per year,” Miller said. “So it’s sort of like a double knockout punch for these plants that used to be mainstays of landscaping for the Pacific Northwest.”

Elizabeth Hodgson is a landscape designer in Oregon and a director at large of the Oregon Landscape Contractors Association. She fielded calls this summer from people trying to save their rhododendrons.

“They don’t need much water but the heat was so detrimental to them,” she said. “There was really nothing we could do.”

Miller said fruit trees have become especially susceptible to funguses, as well as some varieties of roses. Overall, he doesn’t recommend home gardeners plant fruit trees.

“I’d say people’s time and energy would be better spent just buying delicious apples from the farmers market, from people who are equipped to take care of the trees properly,” he said.

Fortifying landscapes through the soil

To begin fortifying properties against the impacts of climate change, Miller tells people to start with their soil.

“That’s one of the very first things you can do to help drought-proof your property or your plants, is to prepare the soil well,” he said.

This involves adding organic matter like compost to soil and adding woody mulch to the surface to help the soil maintain moisture and stay cool. He said a healthy layer of soil called humus, where the soil is dark and filled with organic matter, can stay put for 1,000 years or longer. 

“It is the best step that people can take to drought-proof their landscape, and get plants off to a good start,” he said. “And one of the biggest mistakes I see people making is that they just don’t take the time and effort to prepare their soil well for installing new plants.”

Focusing on drought resistance

Despite the stresses many native plants are under as extreme weather events occur more frequently, Miller suggests starting by planting native species of flowers and trees that are accustomed to the region’s Mediterranean climate. Much of Oregon is considered to be such a climate due to its latitude, proximity to the ocean as well as the warmer, drier summers and wet winters, he said.

As the state experiences longer periods of warmth, plants that survive in California are now even more likely to survive in Oregon. Subtropical plants like the pineapple guava, or feijoa, a fruiting shrub native to parts of South America, could one day grow in Oregon, according to MiIller.

“I would really just caution against high water needs plants,” he said. “Because we know that we’re going to continue to face drought, and it’s going to get more and more expensive to keep watering stuff.” 

Hodgson said more of her clients are interested in creating Xeriscapes. Such landscapes that require minimal water and use efficient irrigation systems like drip lines that slowly apply water at a low pressure.

She said most clients, however, are not motivated by environmental concerns.

“Lately, because of hotter, warmer weather there are concerns with water usage mostly because of the high cost of water,” Hodgson said. “Especially for clients with larger properties, the incentive is to lower the cost of water.”

Planning for fire resistance

Miller said reducing wildfire risk to a home or building starts with creating a buffer. 

“Having an irrigated landscape, making sure that trees are limbed up and that there’s not a lot of brush, that’s number one of what people can do,” he said. 

Limbing trees means removing the lowest branches. Dead and dying trees should be removed as well, because besides burning quickly, they can crash onto houses and other structures, he said. They’re also dangerous in extreme wind and rain.

According to the National Fire Protection Association, the goal of landscaping around a building in an area of wildfire risk is to keep a potential fire on the ground and out of the tree canopy. To do this, the association recommends getting rid of small conifer trees that grow between more mature trees and, when planting trees, keeping them at least 30 feet away from homes and spacing them so each treetop is 6 to 12 feet apart from one another. 

Recommendations from the U.S. Department of Agriculture include planting supple, leafy green shrubs and flowers near buildings, avoiding anything with twigs, needles, waxes and oils. 

Harnessing the power of lawns

Lawns get a bad rap, according to Miller.

“They’re actually really good at capturing carbon from the air and putting it into their root system.” 

Sequestering and storing carbon dioxide is seen as critical to slow climate change. 

Special techniques, like mulch mowing, can turn grass into a fertilizer. Mulch mowers have special blades that cut the grass into tiny shreds that dry and disintegrate quickly, returning nutrients from the clippings to the lawn and the soil, reducing the need for synthetic fertilizers.

“If one does specific practices in terms of mowing, like using a hand mower, an electric-powered mower or a mulch mower, it’s actually a reasonably sustainable land-use option,” he said.

Miller said the environmental benefit of a lawn disappears when people use gas powered mowers, leaf blowers and lots of fertilizers. 

Lawns can also become problematic if invasive weeds proliferate. 

Because of rising temperatures, weeds that typically remained dormant throughout winter will grow and put out shoots earlier in the year. 

“Expect to see a change in the distribution of weeds, both in terms of latitude and also elevation,” Miller said.

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