The Woodsman: More Darned Invasive Plants: Vinca, Holly, Daisies

With all the crazy (and worse) news these days, you may not know that there’s actually been some good news. On June 24, the Washington State Department of Agriculture banned the sale and distribution of English ivy and its cousin Atlantic (or Boston) ivy. Oregon prohibited the sale of English ivy in 2010.

Why? Forests choked with ivy is why — along Highway 26 and Barlow Trail Road between Tim Rim and Brightwood, for example, where tree trunks are covered with ivy. Not only can ivy climb trees and eventually suffocate them, it also overwhelms the understory plants and wildlife habitat. Ivy spreads quickly and is very difficult to get rid of. Portland’s Parks & Recreation Department has had a No Ivy League since 1994, a group of city employees and volunteers dedicated to removing ivy from Forest Park and elsewhere.

In past columns I’ve written about the evils of ivy and other aggressive non-native invasive plants, such as Armenian (Himalayan) blackberry and Scotch Broom, both found all too often in our area. The Oregon State Weed Board (OSWB) lists 139 invasive species in Oregon, all of them brought here and spread, intentionally or otherwise, by people.

In recent weeks I’ve seen a lot of vinca, also known as periwinkle, which is native to Europe, the western Mediterranean regions, and southwestern Asia. Vinca minor (lesser periwinkle) has smaller leaves and flowers than vinca major (big periwinkle). Both were introduced in North America in the 1700s as ornamental plants. Both are aggressive invaders, though not to the degree of ivy or Armenian blackberry. However, Vinca is not listed by OSWB as an invasive plant. 

Periwinkle forms dense mats on the forest floor that excludes native vegetation. Nonetheless, it is commonly sold as an ornamental ground cover. You can buy it from Home Depot, which describes it as “a spreading sea of green foliage, vinca minor will elegantly cover your garden with petite purple flowers.” Naturally, Amazon.com also sells vinca. 

Once established, vinca is hard to get rid of. You can pull up vinca plants, but they can regrow from bits of root left in the soil. Once cut, stem fragments can take root elsewhere, and streams can transport stem fragments along waterways.

Thinking of planting vinca in your yard? Please don’t. 

Lately, I’ve cut a large number of English holly shrubs or small trees in our area, in people’s yards and in forests. English holly, also known as Christmas holly — “deck the halls with boughs of holly” — is native to western and southern Europe, northwest Africa, and southwest Asia. It was brought to the US as a landscape plant but, as with so many other imported plants, proved to be invasive in forests, where it thrives in shade and crowds out native species. Birds love the bright red berries and spread them far and wide. Note that the berries contain alkaloids that can be toxic to humans and pets.

When AntFarm Community Wildfire Defense Program crews clear trees and brush from around homes, they usually chip the material for use as mulch. But they never chip English holly, since the berries might sprout wherever the mulch is spread. 

English holly is not listed on OSWB’s list, but in December 2024, the Clackamas Soil and Water Conservation District named English holly its Invasive Weed of the Month. The district recommends removing holly when the plants are small, when they can be easily hand pulled or dug up. Root fragments left in the soil can sprout, so you’ll want to check the area regularly and pull any new sprouts. The district website states that “removal of larger plants may not be feasible and could cause extensive soil disturbance and erosion. In this case, a cut-stem approach that uses a combination of mechanical and chemical control is more effective and may be less damaging to a site. For additional information on this approach, contact the District’s WeedWise program at 503-210-6000.”

Check the WeedWise web page (conservationdistrict.org/weedwise) for more information about this and other invasives — all 221 of them.

Oregon grape has spiny leaves that look similar to English holly leaves. Instead of using holly for your Christmas greenery, use leaves of our abundant native Oregon grape. Most people won’t know the difference.

This spring you may have seen and admired the flowers of another non-native invasive: oxeye daisy, which are similar in appearance but smaller than the Shasta daisy, a common ornamental. Despite its name, the Shasta daisy isn’t native to the Mt. Shasta, California, area: They are a hybrid plant created by American botanist Luther Burbank in the late 19th century by crossing several European and Japanese daisy species. (Burbank also is responsible for the presence of Armenian blackberry in North America. Thanks, Luther!)

Both oxeye and Shasta daisy are imported ornamentals that have naturalized in the Pacific Northwest. However, oxeye daisy has spread farther and wider. You likely saw oxeye daisy growing along roads and in fields in our area this spring. Although this attractive plant is far less of a problem than ivy or holly, it can out-compete native plants and grasses. 

The take-away message: When shopping for landscape plants, be careful not to introduce non-native plants that may look pretty but will spread to our forests and natural areas.

Have a question about invasive plants? Remember the name of the sci-fi movie about plant-like invaders from outer space? Let me know.

Email: SWilent@gmail.com.