Scott Swanson
Moss is growing like a weed in Sweet Home this winter.
The green sheen that’s spreading across roofs, on walls and on streets and sidewalks, is, those who deal with it say, the result of a combination of factors.
“We’ve definitely noticed it,” said Pat Wood, maintenance supervisor for the City of Sweet Home Public Works Department. “My whole house is inundated.”
Wood believes the small soft plants, part of the plant division Bryophyta, are proliferating in Sweet Home because of increased shade and the wet weather the community has had in the last year. According to the U.S. Army Corps of Engineers, Sweet Home had 67.7 inches of rain in 2012, compared to 51.71 in 2011 – an increase of 16 inches.
A THICK, HEALTHY FOREST of moss grows on a retaining wall on 4th Avenue.
Daniel McGrath, an Oregon State University Extension vegetable crops specialist for Linn County, agreed.
“We had a long fall and a long, wet spring,” he said. “It was kind of an unusual year.”
U.S. Forest Service botanist Alice Smith, who’s a member of the Sweet Home Tree Commission, said mosses are “very active, they’re at their peak right now.
“When they dry up, they don’t die, they just dry up. We’ve had a lot of moisture and they’re loving this fog – as long as it stays above freezing.”
McGrath said he hadn’t particularly noticed that moss was on the rise, but he said climate change may be responsible.
“The climate is changing,” he said. “We know, for example, that insect populations move depending on climate. We know insect populations are moving north. Bark beetles are moving into Canada. It’s possible that moss is a result of that.”
Woods said he thinks the warmer fall, combined with early rain, may be to blame. Also, he said, trees planted years ago in the city have grown and are creating more shade, which is what attracts moss.
“Quite frankly, as the town gets older and trees we’ve planted get taller, I think we’re going to have more moss,” he said.
Smith noted that the moss varieties differ, depending on where they are located.
“Different substrates have different communities of mosses,” she said. “Mosses that grow on a tree are different than the ones that grow on the road.”
Some residential streets are nearly covered with the green growth, though collector routes such as Long Street, Elm Street and 10th Avenue, do not have the proliferation because of heavier traffic, he noted.
He said the city continues to sweep residential areas monthly and collector streets weekly, but the brush on the truck only sweeps a 2-foot swath near the curb, though the vacuum covers a 5-foot-wide area. Plus, he said, many of the older streets have small cracks that allow the moss to get a foothold and since it stays close to the ground, it escapes tire traffic and brushes.
Wood said he has noticed that residents “no longer really take care of their things like they did when I was a kid. It used to be more of a feeling that ‘I’ll trim my stuff up before it bothers my neighbor and he says something to me,’ or pride. Over time, there’s become more expectation that the city or someone else will do it.”
He said the city hasn’t budgeted money for moss control, and with more stringent environmental laws, it’s harder to come up with solutions to the moss problem – particularly on streets.
“Definitely, in the last 10 years, really 20 years, the reduction of chemicals through the EPA lends itself to allowing moss to grow more,” Woods said. “It used to be that you could sprinkle Tide laundery detergent on your roof, but since they took phosphate out of laundry detergent, they go up there and it doesn’t work any more.”
McGrath said that the best way to kill moss on roofs is to use metal – a copper wire strung along the ridge.
“The wire will slowly leach copper and over time that will help to reduce the amount of moss on the roof,” he said. Salt-based driveway applications also include metal as an active ingredient, he noted.
Moss growth in a lawn is actually a different scenario, McGrath said.
“If moss come in, the grass is weak,” he said. “That’s what it’s telling you. The first thing thing to look at is whether you have the right species of grass.”
Some grasses are more tolerant of shade than others and if seed mixes don’t favor shade-loving grass, chances are moss will make an entrance. Also, he said, people tend to mow their lawns to “tightly” in the spring when the grass is establishing itself.
“They scalp the grass, kind of weaken the grass,” he said. “We all do it.”
McGrath suggests mowing at 1-1/2 to 2 inches.
“That allows the lawn to feed its roots and get strong.”
He suggests raking and seeding bare patches, then covering them with potting mix and using adquate fertilizer to keep lawns healthy, making sure there is enough moisture and that the soil isn’t too acidic.
Moss can create problems in trees, particularly fruit trees, if it gets too heavy, he said. He suggests pruning to let light into the tree and using dormant sprays such as lime sulphur.
“Generally, in a commercial setting, you will prune to reduce the amount of fruit and let light in, since shade gives moss a competitive advantage. You can focus on killing the moss or do what’s right for the target crop.
“What you really see is moss coming in and being competitive, putting the target crop, whether it’s grass or apples, at a competitive disadvantage.”
Smith said moss generally is not really a problem for trees – or elsewhere, though many people think so.
“They’re not hurting the tree. They’re not like parasites on the tree,” she said. “They’re just hanging there.
“People think moss is a problem but the Japanese make whole gardens of moss.”