What is common reed (phragmites)?

Common reed, almost always called phragmites, is a giant perennial grass that grows in wet ground. Getting the phragmites identification right matters, because most stands in Pennsylvania are a non-native strain from Eurasia that spreads aggressively and crowds out nearly everything else.

A native form of common reed also lives here, but it’s much less common and grows in looser, better-behaved stands. The invasive strain forms solid walls of stems 6 to 12 feet tall or more, blocks views and water flow, and shades out cattails, sedges and wildflowers.

Phragmites isn’t on Pennsylvania’s noxious weed list, but the non-native form is listed as invasive by PA DCNR, and land managers across the state work to control it.

Phragmites identification: what to look for

From a distance, phragmites is easy to spot: a dense, uniform stand of very tall grass with fluffy plumes on top. Up close, check these features:

• Height: usually 6 to 12 feet, sometimes taller.
• Stems: stiff, hollow and cane-like, often dull tan on the invasive form.
• Leaves: long, flat, gray-green blades up to about an inch and a half wide.
• Plumes: large and feathery, purplish-brown in late summer and fading to tan or gray.
• Winter look: dead stalks and plumes stay standing all winter, so stands are easy to map after leaf drop.
• Underground: thick, tough rhizomes, plus runners that creep across bare mud.

Where it grows in Pennsylvania

Phragmites needs moisture. You’ll find it in marshes, along ponds and stream banks, in roadside ditches, stormwater basins and wet low spots in fields. It also moves into disturbed ground where water collects, such as construction sites, pipeline cuts and spots where fill was pushed into a wet area.

New stands often start from rhizome pieces carried in fill dirt or on excavating equipment. On properties in our river valleys and along the old farm-field drainage ditches, it tends to show up first where the ground stays soggy most of the year.

Phragmites look-alikes

The native subspecies of common reed is the trickiest look-alike. It usually grows in thinner patches mixed with other plants, has smooth, shiny stems that are often reddish near the base, and its leaf sheaths fall away easily in fall. The invasive form has duller stems, sheaths that cling tightly, and very dense stands. If you’re not sure, Penn State Extension can help confirm which one you have before you start treating.

Reed canarygrass is shorter with a tight seed head. Johnsongrass has a white midrib on each leaf and prefers drier ground. Cattails have sword-like leaves and brown cigar-shaped seed heads. Purple loosestrife often grows in the same wet spots but is a broadleaf with bright magenta flower spikes.

How to get rid of phragmites

Here’s the honest truth: pulling, mowing and cutting won’t kill phragmites. The rhizomes store so much energy that the stand simply grows back. Control means killing the rhizomes, and that almost always means a systemic herbicide over at least two seasons.

Mechanical help. Cutting or mowing can make a stand easier to reach and treat, but wait about eight weeks after cutting before spraying the regrowth. Very small new patches can sometimes be dug out completely, rhizomes and all, if you catch them early. Bag the pieces and don’t spread soil from the spot.

Cultural steps. Phragmites follows water and disturbance. Fixing drainage on a soggy low spot, keeping fill dirt from unknown sources off your property, and replanting treated areas with native grasses or turf all help. Avoid digging or driving through a treated stand, since broken rhizomes can resprout.

Herbicides. Penn State’s vegetation management team recommends systemic herbicides applied later in the season, roughly July through October, when sugars are moving down into the rhizomes. Glyphosate in a formulation labeled for aquatic sites and imazapyr are the common active ingredients. Imazapyr is more effective but stays active in the soil and can harm nearby trees. Read and follow the label every time; the label is the law, and the product must be labeled for wet sites if you’re near water.

Treating plants growing in standing water in Pennsylvania requires an aquatic-certified applicator and a PA Fish & Boat Commission permit. Any herbicide application for hire also requires a PA Department of Agriculture pesticide applicator certification. For anything bigger than a small patch, this is a job for a licensed vegetation-management company.

Keeping it from coming back

Expect a second round of treatment the following year, then walk the site each summer and spot-treat any new shoots. Once the stand is dead, the old stalks can be cut or mowed to let light reach the soil.

Get something growing in its place quickly, whether that’s native wetland plants, a seeded grass mix or lawn on drier ground. If the area is wet because of a drainage problem, correcting the grade or adding drainage can make the spot less welcoming to phragmites for good. Keep in mind that work in an actual wetland can require permits, so check before you dig.

Questions we get about common reed (phragmites)

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