Lena Tucker surveys trees planted on the grassy lawn of Sankey Park.
They’re young trees, eight, 10 feet tall. A flame vine maple, a purple flowering plum by Weddle Bridge, a dogwood.
Securely attached to the lower trunk of each is a 20-gallon thick tarp-like plastic bag.
“They’re called Gator bags,” said Tucker, a member of the city Park and Tree Committee. More on the bags in a moment.
Tucker learned about arboriculture during a nearly 30-year career with the Oregon Department of Forestry.
She started with ODF as an intern after graduating from Northern Arizona University with a degree in general forest management, then worked around the state – Astoria, Grants Pass, Prineville, before serving as district forester for Sweet Home from 2004 to 2012.
She then headed the Private Forest Division in Salem and then was deputy state forester before retiring in the summer of 2021.
Since then, Tucker has been active not only with the Park and Tree Committee, as well as working with the landowners in the Linn County Small Woodlands Association.
One of her biggest focuses has been tree health in city parks, and that’s how she got interested in Gator bags.
Heat waves in recent years have put park trees (and others) under stress, and they can’t draw water through their vascular tissues and so they shut down the tiny “stomata” pores on the surface of their leaves to shut down transpiration, the process where plants release water vapor into the atmosphere, Tucker explained.
“But that’s like a short-term solution, because then the tree kind of starves itself,” she said. “So they do that for short period of times, or they’ll the upper leaves will wilt and drop, so they kind of shed those leaves so they don’t have to keep going. But then that doesn’t help with growth of the tree.”
According to ODF literature, symptoms of drought-stressed trees can also include uneven (asymmetrical) tree crowns, scorched leaves, top kill (where the top of the tree dies) and reduced growth (trunk diameter, needle length).
Another problem for trees under stress from drought is that they send out chemical pheromones “that tells every bug in the country, ‘Hey, I’m in stress!’ and then the secondary effect is usually a beetle infestation.”
That’s the reason for the bags, which are perforated with tiny holes that allow the water to slowly drain over a period of about 24 hours.
The goal, Tucker said, is “getting them a good, healthy start early on, until they establish a good root system, and then they can draw water naturally.”
She noted that the established cherry trees in Sankey Park, which have been in the ground about 10 years, are all doing fine because they’ve done that.
“With our new trees, at least up to 4 years old, I want to just try to make sure we get good root growth,” she said, adding that quick, shallow watering from the park irrigation, which doesn’t tend to help produce good root development.
“We’ve planted lots of trees 10, 15 years ago that we just didn’t fuss over so much because we had adequate spring rain, winter rain, and things got established easily,” Tucker added. “But now it seems like we’ve got to add some extra effort to keep them going.”
For the homeowner, Tucker advises making sure that a 1- to 3-year-old tree gets at least 10 to 15 gallons of water a week during the height of the summer “in a long, slow soak.” Trees 4 to 10 years old should get 20 to 25 gallons a week.
The International Society of Arboriculture recommends providing 10 gallons per inch of trunk diameter during the dry season when trees are trying to grow.
She noted that there are many variations of the soaker bags, made by different companies.
“If you don’t want to buy the tree water bag, an easy solution is a five-gallon bucket, put some micro perforations in the bottom. Fill your bucket up with your hose, let it sit. It does the same thing.
“Lawn sprinklers water, but they water shallow, right? And so you’re trying to get this down, down deep, to the root wall of the tree.”
Also, watering should be done during the cooler parts of the day, preferably morning, and it’s a good idea to put 3 or 4 inches of mulch – wood chips rather than bark – in a flat ring (not mounded) around the base of the tree to retain moisture.
One proviso: “If you do choose to use these plastic water bags, you do want to take them off during winter, because you don’t want all that plastic holding moisture around the tree, because then you introduce other diseases,” Tucker said.
There are other challenges for trees in the park. Tucker suspects the reason two Douglas firs near the new playground area are suffering – they’re loaded with cones, which is an indication of that, she said, is because of nearby concrete work.
“I’m thinking the impact of the changes in infrastructure really shocked them a little bit with roots, and made them a bit more susceptible, especially if you’re cutting out some of the fine roots,” she said.
“Then again, we’re kind of back to the inability to move water up. And so they’re not dead because beetles got into them. They’re dead, you know, more of just a, what we call a mechanical injury, probably, to the root systems.”
But dying trees are susceptible to beetles “and we do want to get those out before they impact our other firs,” Tucker said.
For more information on how to cultivate trees successfully, visit www.oregon.gov/odf/Pages/publications.aspx.