You can’t drive along a highway in many parts of North America without seeing mile after mile of a very attractive grass. Tall, with narrow green leaves (beige in the fall) and coiffed with a purplish plume that turns gray in the fall and stays on the plant all winter. It’s such a charmer that many gardeners dig up clumps to plant in their home gardens. And most of them will come to regret that decision pretty quickly.
The grass is common reed (Phragmites australis) and it’s highly invasive. Its creeping rhizomes are dense and incredibly fast-growing. They can reach up to 16 ft (5 m) in length in just one year, with numerous offshoots. Soon you’ll have no more garden and no more lawn. It essentially smothers all surrounding plants, even giving off a toxin to better kill its competitors (it’s allelopathic)! And it’s also very difficult to remove.
This invasive reed is the Eurasian subspecies of common reed (P. australis subsp. australis). It’s believed to have been accidentally introduced to various coastal sites in Canada and the United States in the early 20th century, brought over from Europe in the ballast of ships. Invasive reed now covers hundreds of thousands of acres across North America, but it is especially well established in the North-eastern States, Quebec, Ontario and Atlantic Canada.
It’s a moisture-loving plant that prefers damp sites and commonly starts to spread in ditches, swamps, or near bodies of water. Once established, though, it readily spreads into drier conditions nearby, often taking over agricultural land. It adapts readily to moist soil types, from acid to alkaline and will thrive in standing water up to 3 feet (1 m) deep. It will even grow well in relatively saline soils and brackish water.
There is a native version of this plant: American reed (P. australis americana). The two look superficially very much alike. You can easily distinguish Eurasian reed, though, by its extremely dense growth, with up to 60 stems per square foot (200 per square meter), so it leaves little room for other plants and thus quickly forms a monoculture that repels native wildlife. Also, it can reach up to 15 feet (5 m) high, especially in hot summer areas, shading out fairly large shrubs. And just in case you figure you’ll just dig it up again, the rhizomes can dig down 3 feet (1 m), even 3 yards (9 m) under some conditions, making it pretty much ineradicable.
A Threat to Wetlands
Another problem it that invasive reed dries out the environment where it grows and thus constitutes a threat to the marshes and wetlands.
Canada has declared Eurasian common reed to be that country’s worst invasive plant… and it would certainly be near the top of the list in the United States as well.
The Native Son
As mentioned, there is a North American variant of Eurasian common reed: American reed, P. australis americana. In fact the too look so much alike they are practically indistinguishable, at least for the novice. American reed is, however, a much rarer plant and in fact, is facing extinction as invasive reed continues to crowd it out. If you find it, you’ll note it doesn’t form dense patches, but rather mixes in with other plants, growing here and there, providing an environment where wildlife abounds. It produces few rhizomes and thus remains more or less in place. Also, it rarely reaches more than 6 feet (2 m) high.
Ornamental Grasses You Can Safely Plant
If you want to plant beautiful ornamental grasses, here’s an article that can help you choose: Ornamental Grasses That Stay Put. It explains which grasses are clump-formers (not invasive) and which have creeping rhizomes (invasive). After all, making an informed choice about ornamental grasses is wiser than digging up a potential invader along a roadside.
Controlling Eurasian Reed
It’s too late and Eurasian common reed has already started to invade your yard? Digging, as mentioned, is rarely successful because of the depth of the root system. And never throw harvested rhizomes on vacant lots or put them in the compost if you do try to dig them up: that will just lead to further spreading. Instead dispose of them in the garbage.
Forget herbicides: those available to the general public are ineffective against this species. You can try frequent mowing, which should theoretically weaken it, but in fact, most trials at that level have been unsuccessful: it manages to keep resprouting. Repeated grazing by livestock can help control it, but may not be possible in cities and towns. Burning has been tested and will work, but has to be repeated over several seasons… and is likewise illegal in many municipalities.
Also, don’t expect Eurasian common reed to just die out its own. Some colonies are over 100 years old and show no sign of weakening.
The method that has proved most effective in home gardens is covering the site with black tarp. Mow the stems down in spring and cover the soil in the sector with a thick black industrial-grade plastic tarp. Makes sure the tarp extends beyond the zone currently infested, otherwise stray rhizomes will quickly spread beyond the tarp. (Any that do in spite of your best care will have to be dug immediately.) The tarp can be held in place with rocks or bricks. Leave it in place for an entire year. Common reed depends entirely on sunlight for its survival and cutting off its source of light will weaken the rhizomes to the point where they run out of stored energy and die. If there is still some sprouting after you remove the tarp, put it back in place and wait a second year.
Once the reeds have been entirely eliminated, you can replant (hopefully with something less invasive!) or let nature take its course. Experiments show that once Eurasian reed is eliminated, native species quickly re-establish themselves.
Finally, it may be worth contacting your municipality for advice on controlling Eurasian reed. Many have reed control programs and may be able to help you.
Article first published on this blog on October 27, 2015.