yellow nutsedge — Gardening Hints for the Southeast

yellow nutsedge

Winning The War Against Nutsedge

It’s time to start considering how to fight the horrible garden invader, nutsedge. Today’s guest blog is written by Skip Richter, Horticulturist & Host of GardenLine Radio on KTRH 740. He received his master’s degree in horticulture from Texas A&M University, “the source of all earthly knowledge”, and has served as a county horticulturist with Texas AgriLife Extension for 34 years in Montgomery, Travis, Harris, and Brazos County, advising home gardeners and the green industry on research-based horticultural practices. He has served as the National Gardening Association’s regional horticulturist for the southeastern U.S. and is a contributing editor to Texas Gardener magazine. He was selected as a Regents Service Fellow by the Texas A&M University System Board of Regents.

You can connect with him via:

Website: Gardening with Skip
Instagram:   gardenlinewithskip
Facebook:  GardenLineKTRH
YouTube:   @skiprgarden

Nutsedge (aka “nutgrass”) is not a grass, but rather a member of the sedge family. Listed as the #1 most-troublesome weed in the vegetable, turf and the ornamental categories by the Weed Science Society of America, to know nutsedge is to hate it.

Before we delve into how to control this weed from hell, let’s take a closer look at some important facts about nutsedge. There are two common types of nutsedge: purple nutsedge (Cyperus rotundus) and yellow nutsedge (Cyperus esculentus). They each have key differences that influence which control effort will be effective against them. 

Can’t beat ’em? Eat ’em!

There is a form of yellow nutsedge (known in various parts of the world as chufa, earth-almond and tiger nuts) that’s popular as a snack or mashed food. It is often used to create a sweet, milk-like beverage known as horchata de chufa. The tubers have even been found in Egyptian tombs dating to 3,000 BCE. I think that taking nutsedge with you to the grave is going a bit too far.

I once ordered and grew some chufa nuts (please don’t tell anybody) in my garden to compare them to our regular local yellow nutsedge. They produced tubers that were a bit larger but weren’t very impressive to the palate.

Tubers of our wild yellow nutsedge are also technically edible, with a mild almond-like taste. After chewing awhile, you give up and remove a bit of “sawdust” from your mouth. I’ll note here that edible and palatable are not synonymous. My favorite culinary assessment of yellow nutsedge tubers comes from a National Public Radio story, in which a taste-tester said of nutsedge tubers, “It doesn’t taste terrible.” High praise indeed.

Nutsedge development

Nutsedge often arrives in gardens, lawns and landscapes along with plants, topsoil and/or sod. New plants arise primarily from underground tubers rather than from seeds. Most tubers are found in the top eight inches of soil. But depending on the soil type and the nutsedge species, some tubers will be deeper.

Wet soil conditions wash a substance that inhibits sprouting from the skin of yellow nutsedge tubers, allowing them to sprout. This is one reason why yellow nutsedge proliferates and thrives in wet areas of a lawn or garden.

Nutsedge shoots emerge like pointed missiles from the ground and the leaves emerge from their protective sheath when each shoot reaches sunlight. This protective covering enables them to easily push up through soil or mulch, and even to poke through plastic sheeting and most landscape fabrics when these products are stretched tightly over the soil surface. Once the shoot reaches sunlight and the leaves emerge, and the plant is no longer able to punch through surface coverings.

When a nutsedge shoot reaches sunlight, the plant forms a bulb at its base that produces horizontal underground stems (rhizomes) with new tubers. These tubers can form additional tubers, as well. In one test, a single yellow-nutsedge tuber produced 6,900 tubers by fall and 1,900 daughter plants the following spring. This is one reason this plant is so difficult to control. Diligent efforts to prevent or greatly limit new tuber production are key to controlling nutsedge infestations.

Cultivation and hand-hoeing

Each tuber has approximately seven or more viable buds. So, any attempt at control (such as the ol’ garden hoe) chops off only one shoot; the tuber merely sends up another (after laughing hysterically at the gardener’s efforts). However, tubers expend stored energy to send up new shoots, so prompt removal of new shoots multiple times will weaken tubers and can decrease development of additional tubers.

For hoeing/hand-digging/tillage to be effective, one must remove plants before they have developed more than three-to-five leaves. If left longer, the plants will begin restoring the tuber’s spent reserves. Tubers expend a little over half of their stored energy to develop their first above-ground plant. Therefore, I cannot overstate the importance of constant surveillance and prompt digging or spraying to prevent tubers from replenishing their reserves.

Diligent efforts at frequent cultivation can outlast a tuber’s ability to regrow, but this type of diligent, prompt continual effort is seldom maintained. Control is further complicated by the fact that some dormant tubers are usually present to sprout over time. So, continue to look out for newly emerging nutsedge plants.

Combining control methods

Now that the nutsedge beast sounds impossible to defeat, let me say that it is not invincible. Difficult, yes; but not impossible. You can manage nutsedge, if you use a combination of practices and are consistent with prompt follow-up.

Non-chemical reduction of nutsedge in landscapes and garden beds involves the following practices. While all are not always possible, the more you can do, the better your results will be.
1. Avoid overwatering/saturated soil conditions, which stimulate yellow-nutsedge proliferation.
2. Hand-dig tubers, beginning when the shoots first emerge in spring. If you wait until mid- to late May to begin, you will likely have almost 10 times the number of nutsedge plants you began with. To be effective, repeat-digging is required whenever new plants have developed three-to-five leaves. If you wait longer, the plants will be producing new viable tubers.
3. Rototill the soil to sever rhizomes and bring tubers to the surface, exposing them to dry out. Rake and remove exposed tubers and rhizomes. Sun-drying is more effective against purple nutsedge than yellow nutsedge. Tilling breaks up the underground chain of the tubers on purple-nutsedge rhizomes, causing multiple dormant tubers in the chain to sprout. If you then promptly dig or spray the new sprouts, you can significantly reduce the infestation.
4. Cover future garden beds from spring to fall with a very dense, water-permeable landscape fabric to block out all sunlight. Don’t pull the fabric tightly over the soil surface or else new nutsedge shoots will puncture it. Keep soil moist to promote growth beneath the fabric, which depletes the tuber’s stored reserves.
In a study I conducted in Houston on purple nutsedge, plots were shaded with a loose covering of dense landscape fabric for the summer season. Shaded plots had a 24% decrease in tuber counts, while plots ex-posed to full sun had a 2,400% increase. Also, the 76% of tubers that remained were likely at least weakened, although we did not replant them to check this possibility. While shading won’t eradicate all tubers, it can significantly reduce the number of tubers and can be a helpful part of an organic regimen to manage nutsedge.
5. Solarizing heats the soil and can destroy tubers in the surface few inches. Temperatures over 112 degrees are lethal to tubers. Solarizing won’t destroy tubers deeper into the soil, but if preceded by deep tillage, the effectiveness of solarization can be increased. The clear plastic used in solarizing must be held above the soil surface to prevent it from being punctured.
6. Spray the plants with a systemic product beginning when the first shoots have three-to-five leaves. After the fifth-leaf stage, viable “daughter” plants will be forming on the rhizomes, which will not be effectively controlled by sprays to the original plant. Repeat sprays three-to-four weeks later as new nutsedge plants emerge and have three-to-five leaves.

Organic “top kill” products containing pelargonic acid, ammoniated nonanoate, plant essential oils and acetic acid (vinegar) will kill the weed’s top growth. But they do not do much to control nutsedge, unless accompanied by hand-hoeing.

Suggestions for using sprays

It has been my experience that sprays of glyphosate (such as Roundup and other examples) may kill back the above-ground parts of nutsedge plants but do not provide significant effective control of tubers. Preemergence herbicides used to prevent weed seeds from establishing new plants are of little benefit because nutsedge plants arise primarily from tubers, not from sprouting seeds.

Several products are available on the market to control nutsedge. Repeat applications will be required for effective control. The addition of a surfactant helps the spray stick to and penetrate the waxy nutsedge leaves more effectively. Note that Sedgehammer Plus already contains a surfactant. Note that some products can take two weeks to provide visible symptoms, so be patient. 

Carefully read and follow all directions on the herbicide label. Product formulation and labels can change. The label is the final authority, including over comments made in this article.

Drought stress results in poor nutsedge-control results. Avoid applications of postemergence products to turf stressed by drought or other factors, making it more susceptible to herbicide damage.

Wiper applicators can be helpful

When applying an herbicide product around desirable plants that may be adversely affected, it is best to use a wiper-type applicator to help avoid contact with desirable plants. Wipers apply a small amount of the herbicide directly onto the weed’s foliage, which outcome significantly limits pesticide application rates, environmental concerns and damage to desirable plants nearby. If you’d like to build a simple, inexpensive weed wiper, I have instructions on my website that include product-ingredient names for controlling various types of weeds and trade-name examples.

Nutsedge, although a tough, formidable foe, is not invincible. With diligent, determined, consistent efforts, it can be managed in a home garden and landscape. So, I’ll leave you with these immortal words from the venerated coach Knute Rockne, as they are fitting for the task at hand: “When we get them on the run once, we’re going to keep ’em on the run! … and don’t forget men, today is the day we’re going to win! They can’t lick us, and that’s how it goes! … go in there and fight! Fight! Fight! Fight! Fight!” 

Nutsedge

Sedges have edges.
Rushes are round.
Grasses are hollow
right up from the ground.

There are different versions of this poem, but the first two lines are always the same. I learned it from the Clemson University Extension agent who taught weed identification to Master Gardeners. Why is the distinction important? Because chemical herbicides that are meant to kill dandelions or Bermuda grass, for instance, will have little to no effect on nutsedge, an aggressive and persistent perennial weed.

Purple nutsedge has the reputation for the worst economic impact of any weed. Fortunately (I guess), my part of the world is instead plagued by yellow nutsedge. Yellow nutsedge is more widespread than its purple cousin because of its greater cold tolerance. Nutsedges can be identified by running one’s fingers over the stem. Unlike a round grass, a sedge has sharp edges along its triangular stem. Hence, “sedges have edges.”

In a mixed lawn (I love that term!) like mine, several grasses mingle to produce a thick green turf that looks great from a distance or when observed from a car going by at 50mph. Here is a confession. As long as the lawn is somewhat green, I don’t care what its component parts are. I prefer to spend my time and money in borders and beds. I have zero desire to host a golf course-like lawn.

Back to the subject. Nutsedge has a bright green leaf blade that can mimic innocent grass. You may not detect its presence until you spot the tell-tale seed heads that look like tiny porcupines. The seed heads are not the major troublemakers, though. Even while the above-ground portion is small, it is spreading underground by rhizomes and the formation of tubers (called nutlets) along the roots. When cold weather kills the top growth, the roots remain alive. An individual plant can spread roots to 10 feet wide or more.

Plant seeds, roots and nutlets can spread via contaminated topsoil, be carried along on tools, or be brought home in a new plant purchase. Growers are not evil people. They do their best to provide a weed-free product. But even growers can only do their best.

Nutsedge thrives in soils that remain damp or where lawns are mowed too short, but will grow in just about any soil and in any light conditions. The Extension agent explained that proper timing of herbicide application is critical to success. The best time to apply chemical controls for nutsedge in the earliest spring, before it starts producing those underground nutlets. Products applied later are less effective or even useless. Garden centers stock several products that are targeted solely for nutsedge control. (My favorite product name is SedgeHammer. Wish I had thought of that name.) When mature plants are poisoned, they will abort their own roots to protect the nutlets from falling victim to the herbicide. It will appear to the gardener that the problem is resolved, with all the visible leaves brown and dead. Underground though, those tubers are waiting to regenerate and can be viable for up to three years. Where only a few plants are present, perhaps in flower beds or containers, you can lift the sedge carefully, being sure to get the entire network of roots and tubers. For larger areas like lawns, you may need to apply the appropriate targeted herbicide at the proper time for several consecutive years.