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Environmental Services

working for clean rivers

Phone: 503-823-7740

Fax: 503-823-6995

1120 SW 5th Avenue, Room 1000, Portland, OR 97204

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Alien Plant Invader: Blessed Milk Thistle

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Help Environmental Services get a jump on this invasive, non-native species.

Blessed milk thistle presents something of a dilemma. On the one hand, it is grown for the herbal supplement market; on the other hand, it has escaped cultivation and is over-running parts of California. For the time being, milk thistle is uncommon in northwest Oregon. Let’s keep it that way! Early detection means that we have a chance of eliminating this alien plant invader from Portland.

Blessed milk thistle

Blessed milk thistle is a Required Eradication species in Portland. That means – if you see it, you are required to report it: Call Mitch Bixby with the Environmental Services' Early Detection/Rapid Response Program at 503-823-2989 or email

Where have we seen milk thistle? 

It has been sighted in several locations along the Columbia Slough and on Sauvie Island, and is relatively more common in Clark County, Washington. As with most invasive species, it is typical to first see patches along I transportation routes like railways and roadways. Clark County, Washington, reports active management of several infestations, as does Clackamas County. To date, aggressive management appears to be substantially reducing known patches.

What’s the problem?

Milk thistle is known to form dense patches that originate in open, disturbed areas. Like other thistles, these plants have persistent root systems and produce large amounts of windblown seed, making management difficult. Milk thistle reduces plant diversity as other species are displaced. Invasions are of particular concern in forage lands, where milk thistle also poses a health hazard to livestock.

How can you identify milk thistle? 

Milk thistle can grow to be six feet tall with distinctive white stripes in the leaves. Milk thistle is also very spiny, more so than bull thistle, with flowers and seedheads ringed by exceptionally sharp spines.

Distinctive white stripes on the leaves can help distinguish blessed milk thistle from other thistle species.

Sharp spines adorn the flowers and stems of the blessed milk thistle.

What can folks do about it?

Control where it goes

  • The best way to do this is to treat plants in the spring, before flowers form and increasing the risk for seeds to blow away.

Control where it grows

Dig: Cutting and digging is possible, but not especially effective on larger infestations. These are also particularly spiny plants, which discourage casual handling.

  • Treat: Low rates of herbicide appear to keep milk thistle under control.
  • Check: monitor the site at least annually, and especially years two and three after treatment, as any surviving seed takes its big opportunity to sprout!

If you suspect you’ve found milk thistle, the City of Portland requires you to report it.  Still, because of its prickly nature, you may decide to take advantage of the free management assistance available from the city.  You can report suspected patches to Mitch Bixby with the Environmental Services' Early Detection/Rapid Response Program at 503-823-2989 or

Come visit Environmental Services at Sunday Parkways this weekend

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The Sunday Parkways season kicks off this Sunday, May 21st in Southeast Portland, and we would be delighted to see you there.

The Sunday Parkways season kicks off this Sunday, May 21st in Southeast Portland, and we would be delighted to see you there.

We’ll be at Ivon Park between 11:00 am and 4:00 pm. Just follow the trail of fish hats (see photo below) to find our booths!

And while you’re waiting to get your very own fish hat, we’d love to answer your questions about what the city is doing to manage stormwater and restore the health of our watersheds.

What: SE Portland Sunday Parkways (route map [])

Where: Ivon Park at SE Ivon St. & SE 47th Ave.

When: Sunday, May 21, 11:00 am – 4:00 pm

22 volunteers + 2 hours = 75 gallons of trash!

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Green Street Stewards from Widmer Brothers, Surfrider and SOLVE take on 10 green street facilities in North Portland

On Thursday, April 20th, 22 hardy volunteers removed trash and debris (including two gallons of cigarette butts!) from 10 green street facilities and surrounding areas in North Portland. It’s important to keep green street inlets clear so stormwater runoff can flow into the facility. Removing trash and debris keeps green streets functioning well and looking beautiful.  Widmer Brothers provided food and refreshments for the volunteers at the end of the event.  Many thanks to our sponsors Widmer Brothers Brewing, Surfrider Foundation, and SOLVE.

For more information about the Green Street Steward program and to adopt a green street near you, please go to

Surfrider has additional clean up events planned. For information go to

Treebate Season Finale April 30, 2017

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It's your last chance to take advantage of Environmental Services' stormwater credit for planting trees

No doubt about it, spring is in the air!  With the return of longer days and warmer weather comes the end of tree planting season (It’s best to plant trees when the weather is cold and wet and the trees are dormant.)  So, if you’ve been meaning to add a new tree to your yard, do it as soon as possible to reduce the risk of transplant shock.  Our handy planting guide gives you some additional tips to help your tree survive the transplant process and thrive in its new home.

With the end of the planting season comes the closing of the annual Treebate program on April 30. What’s Treebate? Every tree growing in Portland contributes to clean rivers, healthy watersheds, and the health of the people who live here. That’s why Environmental Services says “thank you” with a one-time adjustment to your sewer/stormwater/water utility bill when you plant a tree in your residential yard. The larger the tree, the larger the credit, but some rules do apply.


Have you planted a tree that qualifies for Treebate? Give yourself some credit and be sure to send in your Treebate application by the end of the month. Apply online or print an application to mail in by visiting

You’re invited: Southwest Portland Watershed Restoration Open House

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The event takes place on Wednesday, April 26th, from 5:30-7:30 p.m. at the Multnomah Center

Environmental Services works regularly with SWNI and the southwest community to develop watershed plans and projects to improve water quality, address public interests, enhance fish and wildlife habitat, improve infrastructure, and restore watershed functions.  

Come join us to learn about project designs, timelines, goals and partners. Staff will be on hand to answer questions, take feedback and provide information about the range of projects and planning efforts we have on the horizon in SW Portland. A number of exciting projects in SW Portland will be highlighted, including:

Boones Ferry Road Culvert Replacement ProjectTryon Creek flows through a culvert under SW Boones Ferry Road that creates a barrier to fish moving to habitat in upper Tryon and Arnold creeks. Environmental Services is working with many partners to replace the culvert with a bridge. The project has received funding from Metro’s Nature in Neighborhoods Capital Grant Program. Construction is expected in 2018.

Existing culvert at Boones Ferry Road 

Stephens Creek Headwaters Neighborhood Stormwater FacilitiesEnvironmental Services is evaluating sites near the headwaters of Stephens Creek to build neighborhood improvements for water quality and wildlife habitat.  Sites under consideration are adjacent to the Texas Wetland at Custer Park, and at Stephens Nature Park. Improving stormwater management, stream flows and water quality at the headwaters of the Creek will have positive impacts both locally and downstream.

Dickinson Park Stream RestorationEnvironmental Services and Portland Parks & Recreation are working together on a stream restoration project on three acres of forested land next to Dickinson Park. The project includes restoring 68 feet of stream, creating wetland and floodplain benches, and removing an abandoned pump house, footbridge, pipes and other structures. The work will restore natural stream processes and function, connect the stream to the floodplain, and protect the stream channel.

You can learn more about southwest watersheds (Fanno, Tryon and Willamette) on the web at With questions, comments or for more information, contact Becky Tillson at 503-823-7097 or

See you on April 26th!