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Reducing the mess of shed Christmas tree needles

By Scott Weybright, College of Agricultural, Human & Natural Resource Sciences

chastagnerPUYALLUP, Wash. – Nobody wants to set up a Christmas tree in their home and have the needles start falling off well before Santa shows up.

So to help tree buyers, Washington State University researchers are using a $90,000 grant to study the effect of ethylene on needle retention in species commonly grown in the Pacific Northwest.

Gary Chastagner, a professor of plant pathology at WSU, has studied Christmas trees since 1980. He’s made a career out of Christmas tree research, and he said needle loss is a huge concern for the industry.

“There’s some research that indicates ethylene exposure can cause needles to drop prematurely on balsam fir trees,” he said. “We don’t grow those in this area, but we want to see if the gas impacts our trees.”

Branches exposed to ripening gas

Ethylene is a colorless gas, produced naturally in plants, that is often used in agriculture to trigger ripening in fruits.

Chastagner started this line of research when the grant funding came through in October, so results aren’t yet available. In the meantime, he encourages consumers to minimize needle loss by keeping their trees well watered throughout the display season.

An older block of grafted clonal Christmas trees at WSU’s Puyallup research orchard.

WSU has about 15 acres of Christmas trees, including a number of grafted clonal orchards (trees are genetic copies of each other) in Puyallup. Researchers there have baseline knowledge of the needle retention characteristics of each tree in these orchards.

“We’re going to be exposing branches to different concentrations of ethylene for a 24-hour period,” Chastagner said. “Then the branches will be moved to a postharvest display room where we do needle loss testing. We also have a set of branches only exposed to air, as a control.”

Partnership enables research

A companion ethylene study involves exposing branches to different levels of the gas over a simulated seven-day storage period. Those branches will also be displayed and measured for needle loss.

Tree branches will be held in a post-harvest display room after they’ve been exposed to ethylene gas. Researchers will measure needle loss on each branch to see effects of the gas.

Chastagner and his team are collaborating with U.S. Department of Agriculture scientist James Mattheis in Wenatchee, Wash., who has years of experience working with ethylene and apple storage. Chastagner said the research partnership makes this project possible.

“It’s a good marriage of people who have extensive expertise in their own areas,” he said.

Much of the grant, $62,666, comes from the Washington State Department of Agriculture, with the balance from WSU.

Other research ongoing

Chastagner is also using the Puyallup research orchards to work on a $1.3 million grant to learn how the genetic makeup of trees can reduce needle loss.

“We’re using the traditional genetic knowledge we’ve accumulated from trees that either do or don’t shed and taking samples from them,” he said.

Another aspect of the project is looking at resistance to Phytophthora root rot, a disease that can impact water and nutrient uptake in Christmas trees and ultimately kill highly susceptible varieties like noble and Fraser fir.

“This is a first-of-its-kind collaborative effort between researchers with diverse expertise at multiple universities working together to help solve two national problems facing the Christmas tree industry,” Chastagner said. “We normally do regional projects on Christmas trees produced in the Pacific Northwest. This is much bigger in scale.”

Read an earlier article about this research at


Gary Chastagner, WSU Puyallup plant pathology, 253-445-4528,
Scott Weybright, WSU CAHNRS communications, 509-335-2967,


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