What considerations should be made when terminating a cover crop?
This Lesson Plan is part the Gardening Module of SustainEd Farms' virtual programming.
Background: Turning Your Garden Beds
The utility of planting cover crops cannot be overstated: they are wonderful sources of ground cover and organic matter content, simultaneously suppressing weed pressure and restoring nutrients to the soil -- collectively invigorating microbial life; their presence alone decreases rates of erosion simply by having roots in the soil for longer durations of various seasons; and they provide refuge for beneficial insects during critical flower emergence periods. In fact, the use and management of cover crops on a large scale is now at the forefront of strategies to offset and sequester global carbon emissions, making it one of a few “solutions” to mitigating climate change from a scientific perspective.
Many of these benefits require that the cover crop is eliminated in an environmentally responsible and timely way. While killing plants that one intentionally grew may seem paradoxical, letting a cover crop go for too long will actually enhance weed pressure: the cover crop itself (and weeds) will go to seed, and compete with crops that are actually meant to be harvested.
While some cover crops will not survive winter, many may have seeds that lie dormant until spring, at which point they are able to germinate. The next task is to find the best method -- or mix of methods -- to terminate those plants that survived winter. Most [if not all] current strategies for eliminating a cover crop invoke some environmental disturbance; however, the benefits of certain practices may actually offset certain categorical damages. While the scope of an operation and the availability of equipment will always be limiting factors for choices, sometimes it is to a farmer’s advantage to rely on multiple approaches for killing a cover crop to maximize the benefits of each. In this lesson, the gardener will be walked through a very simple approach to terminating a cover crop by using common tools that can be found at home.
Learning Objectives
Students will be able to...
Effectively terminate a cover crop
Understand the benefits and costs for different methods of terminating cover crops
Academic Vocabulary
graze /ɡrāz/ verb. - the act of foraging in a field (on grass)
Directions
1. Gather your materials. You will need the following supplies:
shovel or trowel (depending on the size of your bed)
2. Watch the following YouTube video to see a demonstration of how to turn your garden beds to terminate a cover crop. Then, follow along with the remainder of the lesson by reading the steps below.
3. Two distinct goals should be addressed for one’s space and equipment availability:
a. The first consideration for terminating a cover crop is to choose a method that will limit environmental harm (common practices with their costs and benefits are listed below). This demonstration, which occurs at a school garden, is performed with just a shovel (or trowel) as the only piece of equipment needed.
b. The second major consideration for terminating a cover crop is determining when to carry out the procedure. When a cover crop is composed of multiple species, then it is likely that the plants will differ in terms of their growing stage at any given time. With the ultimate goal of terminating the cover crop before it goes to seed, knowing about the differences in growth stage among your cover crops will be of importance. Of course, it is also important to allow the cover crop to grow as much as possible in order to supply the soil with the maximum biomass possible (which will help reduce weed pressure and water loss). Generally, for a mix of species, it is advisable to terminate the crop no later than when half of the plants are flowering.
🐄🚜🔥What works best for the environment and the farm operation? … Similarly to killing weeds, there are a variety of approaches for eliminating cover crops. The environmental impact of each method may still vary widely.
Grazing: Using animals to eliminate cover crops serves many purposes at once. It can feed animals, provide manure as fertilizer to the land, work plant residue into the soil, and save money from labor costs. Grazing can cause soil compaction depending on the animal used and environmental conditions, but their effect may not be as harmful as large machinery. Grazing also includes the release of greenhouse gases by the grazers themselves; however, the organic matter worked into the ground in the process can offset this.
Roller Crimping: A roller crimper is an implement that can be used on a tractor to knock cover crops down and kill them by “crimping” (crushing) them. It happens above ground, doing little to the soil below except for the compaction caused by heavy machinery usage. It is very effective at killing cover crops, and it leaves behind a great surface cover mulch.
Mowing: Using a mower to kill a cover crop is generally less effective than other methods, but it does little to disturb the soil underneath (except for any heavy machinery used). Of course, the green manure left behind is extremely valuable.
Using herbicides: The application of herbicides carries attractive benefits and scary risks. It is effective, timely, and can be done with non-synthetic compounds to limit downstream environmental effects. However, herbicide resistance is always a challenge that can threaten the longevity of any operation.
Tilling: Although extremely effective at the task at hand -- killing plants -- heavy and continuous tilling is generally considered one of the more degrading practices in agriculture. Tilling can cause extreme disruptions in soil structure, which then hinders the ability of the soil to hold water, cycle nutrients, and support life in general. On both small and large scales, tilling is often done with machinery that can cause soil compaction. However, certain surface tilling protocols -- such as the one we will introduce in this lesson -- can be done with minimal disruptions and with little equipment on smaller scales.
4. After assessing the types, timing, and goals of terminating the cover crop, it is time to take action. In a small garden space with limited equipment, a shovel can be used to turn over a garden bed and kill the living plants. Aiming at the point where the plant meets the ground, drive the shovel into the plant to sever the shoots from the roots. Dig the shovel blade into the ground, and simultaneously lift and turn the shovel, burying the green parts of the plant. Repeat this procedure for the entirety of the cover crop.
5. Wait another 3-4 weeks before planting anything (this may be a great period to begin plant starts!). This allows time for soil microbes to decompose the plant material in order to make it available to the next round of plants in a timely way.
Additional Resources:
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