Hanging sedge identification and control

Why it’s a problem

Hanging sedge is a fast growing, grass-like plant that can reach 8 feet wide by 8 feet tall. It can grow in a variety of soil conditions but has most success spreading in areas that flood.  One plant can produce a great number of viable seeds every year. Seeds are readily distributed by water, wind, and tires as well as feet, hooves, and paws.  

It forms dense, clumpy colonies that can impact flows of streams or rivers and block fish passage. These dense clumps can be loosened and torn away from a streambank. This process increases erosion and creates more areas of disturbance for its own seeds to germinate. 

Plant description

Hanging sedge is a large, evergreen perennial (2 or more years life cycle) sedge introduced to North America from Europe as an ornamental species. It is adapted to forested areas with damp, rich soil such as along creeks, wetlands, and drainages. 

It grows in large clumps and spreads primarily by seed. It tends to self-sow and spread outside of where it is planted. It can produce more than 20,000 seeds per plant and in ideal conditions, more than 90 percent of the seeds are successful in creating new plants. Seeds spread by water as well as other mechanisms of disturbance and by being planted. 

Be aware of look-alike plants

Mature hanging sedge is much larger than most local sedges and is easy to identify. Younger hanging sedge plants, however, can be more challenging to identify. These younger plants can be easily confused with other sedges that are important to wetlands and wildlife. 

These are the 4 key features to look for:

• Dense tufts or clumped growth form (rather than spreading)
• Large plant size (culms and leaves) 
• Wide leaf blades (dull undersides) 
• Long & drooping flowering parts (spikes) 

Several other species have at least 2 of these characteristics. It is important to be careful to avoid controlling the wrong plant. 

It may be easiest to identify in the winter in sites where it co-occurs with look-alikes. In December, most of the look-alikes are dormant, while the leaves of hanging sedge are still robust. 

Visit Clackamas County’s Weed Wise for more information about identifying hanging sedge.  

Hanging sedge vs. Slough sedge (Carex obnupta)

Slough sedge plants are smaller overall. Their spikes are smaller and can sometimes be erect, whereas hanging sedge’s spikes are always drooping and flexible. 

Hanging sedge vs. Small-fruited bulrush (Scirpus microcarpus)

Small-fruited bulrush is shiny on the underside of its leaves, whereas hanging sedge is dull and bluish-green in color. 

Small-fruited bulrush also goes dormant (dies back) in winter, whereas hanging sedge remains evergreen. 

When in doubt, take photos and share them with us or report them on iNaturalist.

What to do if you find it

Control of hanging sedge is not required in King County, but we would like to know where it is. 

Particularly infestations in riparian areas so we can work to prevent serious impacts. While property owners are not required to control this species, we highly recommend it. 

If you see hanging sedge growing in or near wilderness areas, please contact us.

Control methods

We recommend using a combination of methods to control noxious weeds. In areas with few weeds, it is important to act quickly before they become harder to control. Make a long-term plan as it often takes several years to get rid of most weeds. Start in the least infested areas first and then move into more heavily infested areas.

Manual control

Small infestations may be pulled or dug out. Take care to remove all roots, as plants will re-grow from leftover fragments (short rhizomes). If present, always remove seed structures (spikes) and place in the garbage to reduce spread. Seed removal can be done at or after the flowering stage in late spring/early summer. 

Cultural control

Sheet mulching can be an effective control method in combination with pulling or digging. First, add a barrier of cardboard or newspaper above the disturbed area. Then add a 4-6 inch thick layer of wood chips or another mulch that won’t break down easily. Keep the area completely covered for 3-5 years and continue to monitor the edges of the covered area in the interim. Add more mulch as needed. Reseed the area with native grasses and other plants that won’t require a lot of digging/soil disturbance. 

Mechanical control

Mowing may prevent plants from producing seeds but mowing alone will not kill the plant. Additionally mowing has the potential to spread seeds that stick onto the tires and mower beyond the target infestation. 

Chemical control

Stay safe when using herbicide:

• Always read the label before use. 
• Wear a long-sleeved shirt, long pants, shoes, and eye protection. 
• Follow state and local regulations.

Herbicide may be useful for large, dense infestations. 

Avoid spraying where there is a chance that herbicide will enter a waterway or wetland unless you are using a state-approved aquatic herbicide and have the required permits and licenses to do so. Use of pesticides in water is regulated in Washington state. See Washington Department of Ecology Aquatic Pesticide Permits for details.  

If you are qualified to do so or if your infestation is not near the water’s edge, follow these general best practices: 

• Apply in the late summer or fall on seedlings and clumps. 
• Take care to avoid desirable plants. 
• Use aquatic-approved products in situations where water is present. Follow the product label and all laws and regulations regarding herbicide use on the site. 

For more information contact us or your local weed board.

Disposal instructions

All reproductive parts (flowers, seeds, and roots) should be put in garbage bags and disposed of as trash or taken to the transfer station. 

Another option is to allow the plant parts to dry out. First, remove any flowers or seeds present and dispose of them in the garbage. You can then lay the rest of the plant parts on a tarp, or a raft made out of woody debris.

The most important thing to be careful about is that the roots cannot touch the soil, as plants can regrow from old root fragments.

Noxious Weed Disposal - Washington State Noxious Weed Control Board

Are your weeds piling up? - Noxious Weeds Blog