Organic Methods to Control Nutsedge

Purple nutsedge (Cyperus rotundus, U.S. Department of Agriculture plant hardiness zones 9 through 11) and yellow nutsedge (Cyperus esculentus, USDA zones 8 through 10) are the bane of gardeners toiling to keep their gardens weed-free. Both perennials hold the distinguished honor and classification as one of the world’s five worst weeds due to their aggressive and invasive nature. If luck isn’t on your side and one or both of these weeds take up residence in your yard or garden, rest assured that there are several organic methods of control, though each requires diligence and repeated treatments.

Purple and yellow nutsedges are both referred to as nutgrass, but neither belongs to the family of grasses. This is why gardeners treating the plants with herbicides labeled for use on grass have little or no success, besides the fact that both are resistant to most chemical herbicides. An easy way to tell the difference between grass and nutsedge is by comparing cross-sections of their stems. A grass stem is hollow and round, whereas a nutsedge stem is triangular with stiffer leaves than grass.

Both nutsedges grow in any type of soil but rear their ugly heads more readily in wet conditions. Though they're also equally difficult to remove from a garden once established, they're different from each other in several ways:

The leaf tips of yellow nutsedge are long and tapered; purple nutsedge leaf tips are blunt.

As their names suggest, yellow nutsedge seed heads are yellow; seed heads of purple nutsedge are purple.

Yellow nutsedge has a single tuber at the ends of its rhizomes, while purple nutsedge has a series of tubers along its rhizomes.

Yellow nutsedge germinates earlier in the season than purple nutsedge.

Purple nutsedge has the darker foliage of the two.

At maturity, purple nutsedge is approximately 6 inches in height, but yellow nutsedge can reach a height of up to 16 inches.

Nutsedge does not perform well in sites that are shady.

Covering beds with landscape fabric and then placing a 2- to 3-inch layer of gravel or bark over the fabric helps control nutsedge.

An organic and less labor-intensive method of controlling nutsedges is to solarize the problematic area of the garden. Realize that the area is going to be out of commission for several months while the nutsedge dies, but this method kills the entire plant down to its tuberous underground rhizomes. This process works best during warm, sunny weather. Solarization offers the added benefit of killing harmful fungi, bacteria and other pests that may be residing in the soil.

Shovel

Hoe

Herbicide

Water

Clear plastic

Bricks

Clear the nutsedge-infested area of any existing weeds or garden debris. Either hand-pull or use a shovel or hoe to remove the weeds. You can also spray a ready-to-use herbicide like glyphosate over the area, but you should allow it to dry for approximately four hours before moving on to the next step. 

Once you have the area cleaned of all debris and weeds and the herbicide has completely dried, if you used one, thoroughly water the area. The heat that develops in the wet ground once the plastic is installed reaches down through the soil and helps kill the nutsedge tubers.

Spread a sheet of clear plastic over the area, making sure to cover the entire garden. 

Bury the edges of the plastic under the soil and lay bricks around the edges to keep the plastic in place so no air can enter.

Read the manufacturer's instructions carefully and always use protective eyewear and clothing, such as goggles, a long-sleeved shirt, gardening gloves and long pants, when applying a chemical herbicide. Be careful not to spray desirable plants with the product and use it on a sunny, windless day. Store the product out of the reach of children and pets and keep everyone out of the area until the product dries. Wash your hands and face with soap and water and handle contaminated clothing and gloves carefully after using garden chemicals.

Digging works best with immature nutsedge plants that haven’t developed more than four leaves. During this younger stage, the plants haven’t had time to produce their underground tubers, which, once developed, may make complete removal via digging almost impossible because of the difficulty of removing all the tubers. Each tuber remaining in the ground develops into a new plant, and the tubers can remain active for years.

When digging the young nutsedge plants, use a shovel or hoe and dig down at least 14 inches and approximately 10 inches beyond the surface diameter of each plant to make sure you're removing the entire root system. You might have to repeat this process every two to three weeks during warmer weather.

Another organic option for eliminating nutsedge that also benefits the soil is treating the weeds with horticultural molasses, according to Howard Garrett, the Dirt Doctor. This is a slower process that will likely take two or three applications before the entire plant dies – including its roots. Garrett's recipe treats 9 to 10 square feet.

Liquid horticultural molasses

Measuring cup

1-gallon watering can

Stick

Pour 1/4 to 1/2 cup of horticultural molasses into a 1-gallon watering can.  

Fill the can with water and mix thoroughly using a stick.

Pour the molasses mixture over the nutsedge plants, drenching the area until the soil surrounding the plants is saturated. Repeat as needed. 

Using horticultural molasses is like feeding the beneficial organisms in your soil a dose of carbohydrates, which gives them energy and promotes their activity in the soil. As these beneficial organisms begin their work, they eat away at the nutsedge tubers or nutlets and slowly digest them. You might not think anything is happening, but you can be sure there's a feeding frenzy going on underground. After several treatments, the nutsedge will start to yellow and die. Digging up the treated plants should reveal that there are no longer any tubers or nutlets attached to the root system, which shows the product is doing its job to dispatch the plant.