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Phone: 503-823-7740

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Alien Plant Invader: English holly

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holly plant with snowWe're following the great news about ecoroofs with some bad news about a classic holiday plant: English holly.  

It may seem like a great seasonal gift or decoration, but beware!

These plants can disrupt Portland’s native ecosystems and are good at spreading without much help.  If you toss your holly plant into your backyard, it can grow stems and take root in the soil through a process called vegetative reproduction.

If you already have a holly tree in your yard, read on.  And don’t worry, there’s always room for new holiday traditions!

 

Because of how it spreads, English holly competes for space and water with native plants.  English holly shades out native trees and shrubs, and also sucks up water that native plants need.  The plant also spreads as birds consume the berries and disperse the seeds.   All of this is bad news for the forests and natural areas in our region that provide clean water and habitat. 

large holly treeEnglish holly (Ilex aquifolium) is a Class C invasive species in Portland (see the Portland Plant List for more information).  It is a broadleaf evergreen tree or shrub that typically grows to about 6-15 feet tall.  However, some plants can grow up to 50 feet tall.  Leaves are dark green, lobed, leathery and glossy, with spiny edges. Only the female plants have the familiar red berries.  English holly typically blooms in late April to early May.

There are many ornamental varieties of English holly that can make identification of the species confusing.  Before buying a holly plant, know what species you’re buying and its invasive potential.  Ask your nursery for more information.

Because of its invasive nature, not to mention the spiny leaves and berries that can cause vomiting and diarrhea in humans, dogs and cats, we recommend removing existing English holly plants from your property.  It’s easiest when they’re small!

holly close up photoWhen the soil is moist, small plants can be easily hand pulled or dug up.  All parts of the root need to be removed to limit re-growth, and the area should be checked at least once a year to remove any new sprouts.  Berries should be placed in the trash and the remainder of the plant can be placed in your yard debris bin.  

Removal of larger plants may cause extensive soil disturbance so we suggest a combination of mechanical and chemical control.  Land owners in Portland can contact Environmental Services with additional questions.  

 

Check out this video by West Multnomah Soil and Water Conservation District on removing English holly.  

King County also has some additional information about holly.

 

Invasive species affect us all. They damage our forests, streams and rivers, and property.  Nationwide, damages associated with invasive species are estimated to be $120 billion each year.  In Oregon, the control of invasive weeds and the cost of the damages they create amounts to about $125 million each year.  We know that it costs a lot less to control new invasive plants before they become infestations, so we need everyone’s help.  Find out more about the problems caused by invasive species and why Environmental Services works to stop their spread.

 

Catching up on some reading over the holidays?  Inspired by this slightly balmy weather to get out in the yard?  Check out our other Alien Plant Invader posts:

 

Photo credits: University of Wisconsin La Crosse and King County.

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