Cover crops are one of the most helpful ways to improve soil quality and prevent erosion. But, they can become quite the weed if not handled properly. Cover Crops are meant to be grown as short-term crops between cash crops intended for harvesting. This allows both annuals and perennial plants to be grown for the benefits they provide. Common cover crop benefits include weed suppression, improved soil fertilitiy and tilth, nitrogen generation and scavenging for nutrients, increased water retention, reduced compaction, and some pest control attributes. Different plants may provide different benefits. To experience a well-rounded combination of benefits, consider growing a mix such as the All Purpose Garden Cover Crop Mix.
Because of their unique purpose in being grown during the shoulder seasons, it can be necessary to step in and terminate a cover crop in order to use your planting space as intended during the main growing months. Below you will find some of the most common methods used to kill a cover crop in time for planting. Keep in mind, it is best to allow 2-3 weeks of rest between terminating a crop and planting your next. This time allows the plant matter to break down enough that your new seedlings won’t be robbed of nutrients.
6 Methods of Cover Crop Termination
It is important that cover crops are allowed enough time to grow and develop significant biomass. This biomass will eventually break down and become the nutrient rich soil you are working towards. Because large amounts of plant matter are hard to terminate for planting, start by mowing or cutting it down. This step may kill some plants, but will leave resiliant root systems to continue growing. This is why mowing is usually paired with another method, such as tilling or tarping. For small areas, such as raised garden beds, consider using tools like a string trimmer to knock down crops before they become too big to turn in. We recommend cutting grains when they are about 18 inches tall to easily turn them back into the soil.
Tilling is one of the most reliable methods for killing a crop. It causes the plants to be significantly injured, displaces the root system, and puts the plant matter within reach of soil organisms that will help break down the plant matter quickly. It usually takes little time to do once a crop has already been cut or mowed down. When working in raised beds, we suggest using a turning fork if other equipment is too big for your growing space.
Winter-killed plants are those that are tender to frost and can naturally be killed by cool winter temperatures. This method is one of the easiest for gardeners to use if using no-till practices. To use this method, make sure your cover crop is planted with enough time to develop significant biomass before frost arrives in your area. By the time spring arrives, your garden is ready to be planted in again.
This is a relatively new term that references the process of knocking the cover crop over. This is an important step for using no-till cover crop practices like tarping or solarizing. Using something that is capable of scratching up the plant matter as it is flattened (ex: roller-crimper or power harrow) is preferred by many growers, as this may reduce the amount of time required for covering afterward.
Covering a downed cover crop traps heat, blocks light, and prevents access to fresh air, which accelerates the process of terminating the cover crop. Tarps should be weighed down to prevent airflow and cooling. To successfully kill a cover crop by covering it with a tarp, it is important to complete this step during warm weather. The cooler the temperatures, the longer your crop will need to be covered.
Average Days Covered
50s = 15-25 Days
60s = 10-15 Days
70s = 5-10 Days
80 plus = 5 Days or Less
This method uses the same process as tarping, except a clear sheet of plastic is used. This creates a greenhouse effect that “bakes” the cover crop faster than the tarp method. However, leaving a cover crop for too long during this stage can lead to sterilized soils that lack important soil microorganisms. Crops can usually be uncovered within a couple of weeks.
For additional information regarding no-till growing practices regarding the use of cover crops, check out our blog Choosing No-till Cover Crops.
About the Author
I'm Ashleigh Smith, a native to Northern Utah. I first gained a love of gardening with my grandmother as I helped her each summer. I decided to make a career of it and have recently graduated with a Bachelor's degree in Horticulture from Brigham Young University - Idaho. My studies have focused on plant production while I also have experience in Nursery & Garden Center Operations.
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