kcweeds

Noxious weed shiny geranium spreading on Vashon Island and other places in King County

person inspecting shiny geranium growing on a road on Vashon
Shiny geranium showed up on this road on Vashon Island this spring. Photo by Maria Winkler.

When noxious weed specialists Maria Winkler and Minwook Park drove down a quiet street on Vashon Island earlier this spring, they were alarmed to find a large, dense carpet of shiny geranium lining the road. It wasn’t the first time this Class B Noxious Weed had been found on Vashon, but in the past it had appeared to be limited to just a few properties. Unfortunately, this was only the first of several new large populations that Maria has found this spring, and these are possibly only the tip of the iceberg given the size of the island and how easily the plant spreads. Vashon residents (and everyone in King County) should watch for this noxious weed, report it, control it and, especially, make sure not to spread it.

shiny geranium growing on a bridge
Shiny geranium is growing on a Vashon Highway bridge over Judd Creek on Vashon Island and has been found in several other places as well. Photo by Maria Winkler.

At first glance, this small, rather cute, non-native geranium does not appear to be much of a threat. However, as we wrote in our April 2017 Weed of the Month, shiny geranium (Geranium lucidum) can form huge, dense carpets to the exclusion of other plants. It thrives in semi-shady woodlands and creeksides, as well as in yards, parks, and pretty much anywhere it can get started. Spread easily by seed, it has been moved up along the I-5 corridor and transported between state parks, likely carried on vehicle tires and people’s shoes. King County has quite a few roadside infestations, some of which are alarmingly large and dense.

flowering shiny geranium on the edge of a road
Shiny geranium in flower is somewhat pretty, but it can create dense carpets very quickly such as on this road in Kirkland. Photo by Patrick Sowers.
shiny geranium along a road on Vashon
Shiny geranium creates dense carpets in open areas and can also move in to less disturbed areas, such as on this road on Vashon Island. Photo by Maria Winkler.
shiny geranium on road to Cedar Grove
A dense patch of shiny geranium was found along the access road to Cedar Grove. Photo by Matt Below.

Shiny geranium has also been moved in contaminated nursery stock and other landscaping materials. One new population found this year in Seattle was in a planter box high above the street. It was probably carried there in a nursery pot or possible in potting soil. In past years, we have found it growing in newly landscaped areas in many different areas of the county, again probably moved there as a hitchhiker in a nursery pot or mulch material.

shiny geranium in a planter box with sedums
Shiny geranium found in a planter box in Seattle, possibly hitchhiked in with nursery plants or mulch.

Noxious weed specialists in King County have already found over 20 new shiny geranium infestations in 2018, and that’s only the ones they’ve had time to record. In 2017, the total number of sites was only 44, and that was 19 more than in 2016. Some of the sites might have been missed in the past since the plant is small and inconspicuous at first. However, shiny geranium is also clearly spreading quickly and showing up in new places at an alarming pace.

person pointing to shiny geranium growing in a tree
Shiny geranium seeds spread easily and the plants can show up just about anywhere. Noxious weed specialist Minwook Park points to a small patch in the crook of a tree found on Vashon Island. Photo by Maria Winkler.

The good news is that shiny geranium has shallow, weak roots and can be easily pulled up. After pulling weeds in a large area, a thick layer of mulch will help reduce new weed seeds from germinating.

shiny geranium plant in a hand
Shiny geranium plants are small and easily hand-pulled. Just make sure to bag them up and put them in the trash, not the compost, to prevent spreading them further.

Larger patches are more difficult, but the sooner you start the easier it will be in the future as you deplete the seed bank in the soil. Shiny geranium has been known to germinate several times in a year so it’s important to re-visit the infested areas several times during the growing season to catch all the plants before they go to seed.

shiny geranium growing near rocks with other weeds
Shiny geranium has been found on many properties in Seattle, some of which are quite extensive such as this one where it is found mixed in with other weedy species. Photo by Sasha Shaw.
dense carpet of shiny geranium seedlings by a boot
Shiny geranium grows so densely and germinates so early in the spring that it can overwhelm other plants. Photo by Maria Winkler.

Most important to stopping this plant is quick action. King County Noxious Weed Control Program will try to find ways to help people in King County control their shiny geranium, and our staff may be able to provide assistance if needed. It is in everyone’s interest to stop this plant from spreading more because once it is established, it is nearly impossible to stop. Please alert us if you see this plant in King County. If you are unsure about identification or which geranium you have, you can send a photo by email or we can come stop by.

For more information on shiny geranium, visit our website.

three weedy geraniums in pots
From left to right: shiny geranium, cutleaf geranium and herb Robert. Unlike other weedy geraniums, shiny geranium is a regulated noxious weed in King County and there may still be a chance to contain it and keep it from establishing. Photo by Karen Peterson.

2 comments

  1. Thank you for this post, and the great photos. I am helping to get the word out on Vashon about this one. It would make a great groundcover if it weren’t so incredibly invasive, taking over our low-growing natives like false lily of the valley, native bleeding heart, starflower, bunchberry, yellow violets, native oxalis, and many more….

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