Invasive earthworms also a problem

Taking things a step beyond invasive plants, gardeners should now also watch for invasive species of earthworms, said Kelly Kearns of the Department of Natural Resources.

“The earthworms you’ve known in forests and gardens are all from Europe,” she said. “There are no native earthworms in this area. They are good in the garden, but they are destructive in the forests.

“The new earthworms coming in are from all over Asia, and there are a number of different species. One that’s causing concern is called a jumping worm.

“They appear to be much more destructive than ones we have in our forests,” she continued. “We have only known them in Wisconsin for four years, but we know they completely change the structure of the soil so a lot of plants will die and it will be hard for seedlings to get established.”

Gardeners throughout southeastern Wisconsin have seen these worms in forests and gardens, Kearns said.

“We don’t know how to control them at this point, but there is research going on,” she said.

She added that gardeners can help prevent them from getting in.

“The cocoons and the worms can move in soil, mulch, compost or on soil on your gardening equipment,” she said. “Anything that can move soil or organic matter can move these worms.” Therefore, gardeners would be wise to make their own mulch and compost, she said.

Jill Hapner of Southeastern Wisconsin Invasive Species Consortium said another way individuals can keep the worms out of their gardens is to look for them when purchasing plants.

“When you buy plants, go through the dirt carefully before you plant them, and if you find any worms, throw them in the garbage,” she said.