Calling all ninja warriors

ninja-29569_1280Whaaaaaa! Whu whu whu…weeaah! Is that a non-native, invasive buckthorn shrub growing in your back yard? Here, take my ninja sword and chop it down. Hi-yah! They’ve got us surrounded. The buckthorn are creeping in from all sides. We need more ninjas! Chop, chop, chop – get ‘em!

A ninja costume arrived in the mail at our house yesterday and I spent at least an hour prowling around the outside of the house jumping out of bushes, stabbing imaginary foes, and attempting to scare my son. I’m sure the neighbors thought I had gone crazy. Then I got to thinking, “What if all this slicing action could be put to better use fighting a real enemy like buckthorn?”

Buckthorn has smooth, dark green leaves, greyish bark with little horizontal lines, and long thorns.
Buckthorn has smooth, dark green leaves, greyish bark with little horizontal lines, and long thorns.

It’s hard to believe that one plant could cause so many problems, but buckthorn truly has become a green menace in Minnesota. Since it was first recorded in Minnesota in Hennepin County, 1937, the shrub has taken over thousands of acres of woods and deciduous forests in our state, crowding out woodland wildflowers and native shrubs, as well as spoiling bird habitat and increasing erosion near rivers, lakes and streams. Because it leafs-out early in the spring and keeps its leaves late into the fall, buckthorn enjoys a growing advantage compared to native shrubs. Females produce large numbers of blackish-purple berries, as well, many of which germinate and help buckthorn to spread quickly into new areas from bordering properties.

Truth be told, I know that there are already hundreds of ninja warriors out there in Washington County battling buckthorn. They come by the Washington Conservation District office all the time to borrow orange weed wrenches for the crusade. I know too how frustrating it can be to fight buckthorn if you have anything more than a small city lot. Not only does buckthorn form an impenetrable thicket, spiky and difficult to cut down, but it is freakishly capable of sprouting and re-growing from a stump, unless treated with herbicide, creating a new octopus-like shrub even tougher to defeat than the original. Worst of all, buckthorn seeds can survive for up to five years in the soil, so even if you succeed in removing all of the buckthorn from your land, you’re doomed to continue pulling out emerging seedlings each spring until the buckthorn really stays gone.

Buckthorn wrench in action.
Buckthorn wrench in action.

Although swords may be the weapon of choice for real ninjas, they actually aren’t really the best method for killing buckthorn. In general, there are two standard approaches. The first is to remove the buckthorn completely from the ground, root and all, using a weed wrench so that it can’t grow back. The downside to this strategy is that it disturbs the soil and can make it easier for new buckthorn seedlings to sprout up, or other invasive species like garlic mustard to take hold. Furthermore, if the soil below the buckthorn is completely bare, you’ll need to plant new native groundcover and shrubs to prevent erosion. The second strategy is to cut down buckthorn with a saw, to avoid disturbing the soil. Then, to prevent the buckthorn from re-sprouting, you have to either treat the stump with herbicide (see for info on chemical control) or cover the stumps with a tin can or buckthorn baggie (

The University of Minnesota, Forest Resources Department has been conducting research on the best ways to prevent and manage common buckthorn. After surveying 55 sites in central and southern Minnesota in 2010, researchers found that buckthorn was most abundant in sites with more openings in the canopy and a sparser layer of leaf litter on the forest floor. They also found that non-native earthworms and buckthorn tended to go hand in hand. “Although not immune to invasion,” they wrote, “’healthy forests’ are more resistant than disturbed forests (Whitfeld, et al, 2010).” This month, the Minnesota Terrestrial Plants and Pests Center at the University of Minnesota announced that it will be funding a new $327,000 project, led by Professor Peter Reich, to develop management tools to limit buckthorn re-colonization following its removal.

Though the fight against buckthorn is challenging, controlling buckthorn in residential areas is one of the best ways to protect Minnesota forests from invasion. That’s why I’m calling all ninja warriors today…ready, set, hiiiii-yaah!

To participate in a group ninja buckthorn attack, come to the annual Newport Buckthorn Event at Bailey School Forest on Saturday, Oct. 24, 9am-noon. RSVP to Renee Eisenbeisz at (651) 459-5677 or, by Monday, October 19, 2015, so that supplies and snacks can be arranged.

Learn more about buckthorn at