Cover crops as a learning tool in school gardens

How did farmers grow food before there was synthetic fertilizer?

Do you ever wonder how farmers replenished soil fertility and grew crops before the development of commercial fertilizers? While synthetic fertilizers can result in larger crop yields, when improperly used they also have the potential to negatively impact the environment. Additionally, recent research by Michigan State University and Illinois University show that long-term nitrogen fertilizer use causes nitrogen-fixing bacteria present on the root systems of legume or pea family plants to be less effective.

Prior to World War II, farmers reinvigorated their soils with animal manures, and by alternating their crops with plants nitrogen fixing plants that have beneficial bacteria on their roots in nodules. These symbiotic bacteria convert nitrogen in the air into available nitrogen compounds that plants can absorb. These types of crops are often referred to as “cover crops” because they are grown to cover or protect soils from erosive winter winds and to increase soil fertility.

In the past, cover crop seed was typically only available in large quantities geared toward farmers, and were not sold in smaller quantities in seed catalogues. The past decade has seen resurgence in the research and use of cover crops in home gardens, market gardens and organic agriculture as a practical alternative to commercial fertilizers to increase soil fertility. In response to this new market niche, seed companies have begun selling cover crop seed in smaller quantities that are useful to gardeners and smaller growers.

Cover crops can be a great educational tool to teach students about how plants can replenish the soil without inorganic fertilizers. Michigan State University Extension Oakland County offers a good primer on cover crops or green manures that helps to explain how to improve garden soil by turning under living vegetation.

You can also use cover crops as a real life example of the nitrogen cycle in the garden. Cover crops and the microbes present on their roots are also an example of a truly valuable ecosystem service – adding organic matter and nitrogen to increase the fertility of our soils without inorganic fertilizers. Moreover, planting a cover crop in your vegetable bed provides a home and food for valuable soil microorganisms, suppresses weeds, increases water infiltration and returns organic material and nutrients to the soil.

A good choice for fall planting is winter wheat or cereal rye. Both cover crops will produce some shoot growth in the fall, die back in winter and regrow next spring. Be sure to turn the top growth over next spring before it is six inches tall and gets too fibrous to rapidly decompose, or goes to seed.

If you miss the fall window to plant cover crops, you can still frost seed clover in late-winter. Frost seeding is setting cover crop seeds into soils that are going through the late-winter freeze/thaw cycle. Heaving the soil works the cover crop seed and results in early-spring growth. Allow at least two to three weeks for the incorporated cover crop to decompose before planting your vegetables.

For more information on choosing a cover crop for a vegetable garden, visit the Midwest Cover Crops Council Vegetable Cover Crop Decision Tool. This is a very useful application where you can enter your state and county in and you will be given appropriate planting times for different cover crops. This may also be included in soil lesson for students. More specific information is available by inputting additional information about your soils.

This article was published by MSU Extension and community food systems educators who support farm to school activities, including school gardens.