Publications (Paul's Blog)

June 17, 2010

NUT GRASS

Filed under: Uncategorized — Paul Dowlearn @ 11:32 am

  Nut grass or purple nut sedge (cyperus rotundus) has often been described as the worst weed in the world. Originally from Africa, and apparently eaten by the Zulu tribe (hence the name, Zulu nut), this ubiquitous plant has followed civilization all over temperate parts of the planet. Most of us are not interested in the nutritional value of this plant and would rather be rid of it. Being a student of horticulture I have spent years attempting to beat this plant. And yes, I even tried eating some. I found it very bitter. Apparently the Zulus must have a recipe to spice it up.

  Like many of you, I have tried every new concoction to hit the market only to find that none of these applications really worked long term. Regardless of the claims advertised, as soon as the treatment was stopped the nut grass would return. Only a few at first but soon there was more, and more, and more……………… Eventually, and again regardless of the myriad treatments I have tried, I would give up and console myself that at least I had knocked it back some…………and (thank God) at least this was a short grass that would not get several feet tall like Johnson grass.

   As a youngster I watched my mother wage war on nut grass. One day she decided that she would take a square foot of our lawn and diligently dig the nuts out until it finally gave up. For weeks on end she could be seen working the patch with her weed fork. By midsummer, the patch that had been a mixed batch of lawn with some nut grass had turned into a solid square of nut grass. In her wisdom she admitted defeat and at that point turned her efforts elsewhere. Intrigued, I watched this spot gradually return to a mixed batch of lawn interspersed with nut grass. I did not realize it at the time but my mother had provided me with my first clue regarding nut grass control.

  Later on, as I plied my talents at helping others maintain lawn and garden, I noticed that nut grass was not to be found under thick evergreen shrubs yet I would see it in adjacent areas where bedding plants or lawn grasses were cultivated. From this I deduced that nut grass needed a certain amount of sunlight to grow. This was my second clue but still I had not put it together.

  I remember reading an article some twenty odd years back about an A&M student who decided to hand pull (defoliate) nut grass to see how long it would take the nut itself to run out of energy to grow when denied leaves to produce chlorophyll to feed the nut. Apparently the nuts were still producing when this fellow graduated. From this, he hypothesized that the nuts may be able to remain dormant for as much as 50 years and still be able to grow back. It was this dormant period that got me thinking again. OK, if we can’t kill it, how do we make go dormant? I was getting closer.

  My next lesson came years later when a good portion of my property fell victim to a fire caused by fireworks one Fourth of July. The fire had destroyed all the existing vegetation. Nut grass was among the first plants that appeared after the burn. This occurred at typical hot July temperatures and without a drop of rain. Furthermore, I had not noticed nut grass growing in those areas that had been covered by native plants and partially shaded by trees before the fire. Aha!! I immediately decided that the nuts had been there lying dormant all along. I also decided that the fire burning off the existing vegetation had allowed the sun to warm the ground which in turn must have triggered the nuts to sprout.  Perhaps this much maligned grass did have a purpose in Nature’s grand scheme. The ability to remain dormant for long periods gives this plant an opportunity to grow after fire or some other natural disturbance compromises existing vegetation. Hence nut grass can help control erosion while the former vegetation must wait for beneficial rains to grow back.

  Sure enough, by the next summer the former grasses and trees had returned and the nut grass went dormant. I have not seen it since but I’m certain it is still there…………waiting. Now I had learned enough to begin my own experiments.

  It was easy enough to find a spot infested with nut grass. I had learned that pulling it was futile, smothering with various fabrics and/or mulches didn’t work, any soil disturbance or thinning of vegetation would encourage it, and it did not like shade. I set about using living ground covers as opposed to organic mulches. My thinking was that since this was a short grass it should be easy enough to keep the ground shaded plus eliminate soil disturbance with any fast growing groundcover. It took two or three years for my desirable ground covers to get nice and thick but it worked! I found evergreen plants to be most effective since nut grass does go dormant in winter. The evergreen varieties had a chance to gain a bit during the cold months. I also found the thicker and tighter growth habits worked well even if they were shorter than mature nut grass. I had been successful by changing my tactics from eradication to encouraging dormancy.

  Now I know most of you are thinking, “OK that might work in ornamental plantings, but what about my lawn?” The same method applies. Most folks that have chronic weed problems (including nut grass) are mowing too short, too often, and not concentrating enough on making that lawn grass thick and healthy. The truth is most lawn grasses can choke out anything that is not a large shrub or tree as long as that grass is fertilized occasionally, watered when dry, and mowed   to encourage deep lush growth. Set your depth on the highest notch and watch the nut grass diminish.

  Please don’t forget that this method may take a season or two for satisfactory results. It is a classic example of working with Nature according to her plan rather than seeking a quick fix. Instead of attempting to kill nut grass I opted to cause it to go dormant and hopefully remain that way. Like my mother, I still have the urge to pull it out so I have to resist. So far this method has worked better than any other for me. So just maybe, barring any catastrophe that stimulates the dormant nuts, it will finally die…………….in about 50 years!!??

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