Nut Sedge (Cyperus rotundus), or nut grass as it is often called around here, is one of the most invasive weeds in the entire world. I am not making that up. It is currently listed as invasive in over 90 countries across the globe. Since there are only about 196 countries out there, that means that nut sedge is a major problem for 46% of the entire world.
The origins of nut sedge are most commonly attributed to Africa. However, there are varieties that are native to southern and central Europe and southern Asia. Where ever it came from, everyone that I know wishes it would have stayed home.
In my mind, nut sedge is the quintessential weed. It grows where it is not wanted, it spreads incredibly quickly and it is almost impossible to control. In fact, it is one of the very few weeds that will not be stopped by rubber mulch or plastic sheating. My botanical brother Morgan McBride loves to tell the story of his above ground pool. Before installing it, he stripped the site of vegetation, sprayed with round up and brought in sand to level the site. He worked all of two days to get it all assembled and then he left it alone until the next weekend. When he went out to fill it, 5 DAYS LATER, the bottom of his brand new pool had 50+ nut sedge sprouts sticking right up through the rubber bottom. Needless to say, he hates nut sedge too.
I am writing this post because, once again, I am faced with a major outbreak in one of my beds. Three weeks ago, I cleaned out a large bed. I pulled all of the weeds that I could see, laid down eight layers of newspaper and then covered it all with about 6” of hard wood mulch. Imagine my surprise when I was watering just two weeks later and discovered approximately 100 of these little green devils all over my freshly mulched bed!
Until this last bit of mulching I thought I had eradicated most of it in my beds. I am certain that most nut sedge comes into my yard concealed in the materials that I am applying. There is just so much nut grass in my newly mulched bed that it had to be in the mulch I used. And here in lies one of the major problems with this green devil. You can mulch it, you can dig it, you can compost it and you can run it through a shredder and it will still come back.
Biology of a Pest - Why is nut sedge such an effective weed? Well, the answer lies in its biology. First of all, it’s a sedge. All sedges have a very thick cuticle covering them so many topically applied herbicides do not even get into the plant. And, even if it did, it wouldn’t solve your problem. You might kill the parts of the plant that are showing but the tuber (or “nut”) of this plant is what allows it to come back time after time. This tuber lies deep in the soil and it is connected to the plants by very fragile roots. That’s why pulling it does very little good. You may get what you think is the plant and all of its roots, but in reality, you most likely left the nutlet behind. This nutlet can lie dormant for up to two years.
Another problem with nut sedge is that in addition to the tubers, it also spreads by rhizomes. These underground roots shoot out sideways from the nutlet and create another tuber that will, in turn, sprout another plant. These rhizomes and tubers can be as deep as 14” in your soil. Digging, and I mean deep digging, is really the only way to get rid of this pest in an organic manner.
If you are not of the organic mindset, then there are a couple of chemical products out there that have been shown to be fairly effective against nut sedge. First is a product called Sedge Hammer (which I think is a really cute name). Sedge Hammer contains a chemical called halosulfuron and it is the very best thing out there. It requires you to coat the plant with it through a spray or a direct application. I have used it both ways (in a previous garden, before I tried to be an organic grower) and for me, it was most effective when I used a brush like applicator and actually “painted” each plant with it. Another trade name for halosulfuron is Manage. This product is readily available at most garden centers.
Another effective product is imazaquin. Imazaquin is sold under the brand name of of Image. Both of these products are designed to be absorbed by the roots so you should water soon after application. Also, for best results, treat your nut sedge when it is young. The bigger it gets , the harder it is to kill. Also, don’t be surprised if you have to apply several treatments to get the control desired.
P.S. Round Up (Glyphosate) also works somewhat against this scurge. If using Round Up, make sure to spray when the plants are young, spray often and make sure there is nothing that you care about growing anywhere close to nut sedge.