How to Terminate Cover Crops in the Vegetable Garden

Utilizing cover crops in the home vegetable garden is beneficial to help build soil fertility, suppress weeds, and alleviate soil compaction, among other things. 

Proper termination is essential to receive all the benefits from cover crops. Cover crops that are not properly killed at the appropriate time can become significant and difficult weeds.  In general, cover crops should be terminated 2 to 3 weeks before planting the vegetable crop.  Some species should be terminated before setting seed to prevent unwanted germination the following spring. 

For most home gardeners, utilizing a cover crop that winter kills is the best option.  Cover crops that are killed by cold winter temperatures have the lowest risk of becoming weeds in the future and require the least amount of inputs to manage.  

Large-scale field growers utilize implements like roller crimpers or flail mowers to terminate cover crops.  These devices are not practical for use in a home vegetable garden, so other methods can be used.

Winter Kill  |  Mowing  |  Crimping  |  Smothering  |  Tilling & Digging  |  Herbicides  |  Combinations  |  Methods to Use  |  More Information

Winter Kill

Some cover crop species will not survive the winter.  These cover crops are the easiest to manage and are recommended for use by home gardeners because no special process or machinery is needed for termination.

In early spring, inspect the cover crop to ensure it is dead.  Some species can overwinter if the winter is unusually mild. If the cover crop does not die over winter, another termination method needs to be used. 

The remaining straw-like mulch can be left in place to help suppress weeds and conserve soil moisture.  If desired, the dead material can be tilled into the soil. 

Cover Crops That Winter Kill in Iowa

• Oats
• Teff
• Winter Barley
• Annual Rye
• Sorghum-Sudangrass
• Sunn Hemp
• Field Peas
• Cowpea
• Sunflower
• Buckwheat
• Yellow Mustard
• Rapeseed
• Field Turnip
• Oilseed Radish

Learn more about the attributes of these and other cover crop species in this article: Types of Cover Crops for Use in Home Vegetable Gardens.

Mowing

Termination by mowing can be done with a standard riding or push mower. For most species, termination is most effective when the crop is at about 50% flowering (usually about one week after flowering starts).  

Using a mulching blade, make several passes with the mower set at different heights, working from the tallest setting to the lowest.  For thick or tall crops, use a hedge clipper or string trimmer before mowing to make using the mower easier.  If needed, spread the clippings evenly across the soil surface when complete.  The clippings can be left in place to help suppress weeds and conserve soil moisture.  If desired, the organic matter can be tilled into the soil. 

Crimping

Home gardeners can use a foot crimping tool to break off the plants at soil level and lay them over. This method works well for many grass species.  Crimping kills the plant and creates a straw-like mulch that stays in place. It's ideal for no-till gardens.

Crimping Tools

Foot crimping tools can be purchased or made at home. To create your own, attach a piece of angle iron to the broad side of a 2 to 3-foot-long piece of 2x4 lumber. With the angle iron oriented down, attach each end of a length of rope to either end of the 2x4.  Make the loop a comfortable height for lifting, typically about waist-high. 

How to Crimp Cover Crops

To crimp, start at one end of the garden bed and bend the plants forward by stepping down on the 2x4 to firmly apply pressure and break the base of the stem.  Pick up the board slightly with the rope handle, move it forward 3 to 5 inches, and repeat this process.  Work down the length of the garden in this manner.  When finished, the stems will all be lying over, facing the same direction, forming a mat that can be planted through once they brown.    

Smothering

Cover crops can be terminated by smothering, though this method is time-consuming, often taking 2-6 weeks. It's best to start this method of termination in the fall so the area is ready for spring planting.

Cardboard & Newspaper

If using newspaper or cardboard, lay 6-8 sheets of newspaper or 1-2 layers of cardboard over the cover crop. Thicker layers can block water and air movement, negatively impacting soil microbe health.  Remove staples and packing tape, and avoid waxed cardboard and glossy paper. Cover the newspaper or cardboard with an organic mulch, such as compost or leaf mold, to prevent it from blowing away.  The layer of paper or cardboard should be broken up with a garden fork or broad fork once the underlying vegetation is completely killed, so as not to obstruct water and air movement into the soil for your vegetable plants. 

Plastic

Plastic is another option. Stretch a single layer of light-blocking plastic over the area. The plastic prevents photosynthesis, dries out the plants, and raises temperatures for faster killing through solarization. However, the heat can harm beneficial soil organisms. Secure the plastic with bricks or sandbags. The edges of the plastic can also be covered with mulch, compost, or soil to hold it in place. Remove it once the crops are dead. Afterward, till the dead material into the soil or leave it as mulch. Consider reusing the plastic in future years.  Be sure it is dry before rolling or folding for storage.  Over time, the sun will degrade the plastic and cause it to easily break or tear.  At that point, it should be replaced.

Tilling & Digging

Many species of cover crops can be terminated by tilling, turning, and digging. Home gardens can be dug by hand by turning the soil with a spade, shovel, or garden fork.  Larger gardens can use a tiller, although this method may be difficult as tillers are not always large and powerful enough to fully incorporate the organic matter, and stems often tangle on the tines. 

Start by mowing to break up stems and leaves. Tilling should occur at least 2 to 3 weeks before planting. Only work the soil when it is dry enough, avoiding wet soil that holds its shape when formed into a ball. Be sure to incorporate all the organic matter into the soil. 

Freshly incorporated organic matter begins to break down and the soil microbes responsible for decomposition consume nitrogen in the process. If planting is done too soon after incorporating organic matter, nitrogen-deficiency symptoms may be observed on newly planted vegetables. Incorporating fertilizer before planting the vegetable crop may be necessary to avoid these symptoms.

Herbicides

Utilizing a non-selective herbicide, such as glyphosate, is the least labor-intensive method for cover crop termination.  The dead residue that remains after the herbicide application can remain and become mulch, or it can be tilled into the garden.  

Always read and follow all pesticide label instructions.  Take special note of the wait period before planting and apply the herbicide far enough in advance to allow for planting after that waiting period.

Combinations

It is also effective to combine some of these termination tactics to make the process easier or speed it up.  Any of these methods could be used in conjunction with each other.  

Some combination options include smothering and tilling, mowing and smothering, and mowing and herbicides.

Best Termination Method for Cover Crop Species

Below are effective termination methods that can be used on several cover crop species well-suited for home vegetable gardens.

More Information

• Cover Crops for Home Vegetable Gardens
• Benefits of Cover Crops in Home Vegetable Gardens
• Types of Cover Crops for Use in Home Vegetable Gardens
• Crop Rotation in the Vegetable Garden
• Managing Garden Soil
• Growing and Caring for Your Vegetable Garden
• Planning Your Vegetable Garden

Photo credits: 1: Ajay Nair; 2: Olga/AdobeStock; 3: Ajay Nair; 4: Aaron Steil; 5: apichsn/AdobeStock