Enhancing Cover Cropping Opportunities with Spring Cover Crops

Part III: Harvesting Spring Cover Crops

By Chuck Schembre, Understanding Ag, LLC

NM Healthy Soil partnered with Green Cover Seed to distribute one hundred 25-pound bags of a custom designed spring cover crop seed mix among attendees at the annual REGENERATE Conference, taking place in Santa Fe, New Mexico in the fall of 2023. This article is the third in our three-part series providing guidance on how to plan, plant and harvest a diverse spring cover crop in the Western United States. Click here to read the first article.

^{Happy cover crop seed recipient at the 2023 REGENERATE Conference. Photo by Isabelle Jenniches CC BY 2.0}

Cover Crop Termination Methods

There are essentially five cover crop termination options I consider for maximizing soil health benefits:

• mowing
• crimping
• solarizing
• grazing
• winter kill

All these methods are under a no-till approach. I purposefully omitted tillage from the list because while it is easy to till a cover crop under as a “green manure”, and there may be some short term benefits to this method in a highly degraded soil, I won’t be investigating tillage as a termination method in this article. If your first thought is “how do I direct seed a small-seeded cash crop following a cover crop without tillage”, my response is “change up your rotations so that a small, seeded cash crop does not follow a dense cover crop”!

Each termination method requires a lot of explanation and consideration, therefore I recommend these two resources for understanding how to manage no-till cover crops:

Below I will provide some general discussion and considerations for terminating covers in our three specific farming contexts. I will not be explaining the termination process from start to finish, instead I just want to get some ideas rolling for you to follow up on.

In the Garden and on the Farm 

Termination of the spring cover can occur in late-Summer to early-Fall for a no-till planting of transplanted cool season crops, direct seeded pea or fava bean, and/or garlic planting. In the small garden or market garden, my go-to is solarization or occultation, leaving a decomposing mulch layer on the soil surface ready to plant into. If you have complete control over the moisture and allow the cover to completely desiccate, mowing or crimping is effective to provide a dry mulch residue. Mowing or crimping followed by planting sometimes causes a little nutrient tie up, and I find solarizing the cover increases decomposition of the cover and root system, increasing nutrient mineralization in the process and potentially providing more available nutrients to the proceeding crop.

If you live in a very cold winter climate with plenty of snow, winter killing is a great option to try. It is effortless, and when spring arrives, you will have a beautiful decomposing mulch residue ready to plant into. As mentioned earlier, some species may survive the winter in many climates providing a free winter cover later in the year. If that is the case, early in the following spring the cover can be solarized, mowed, and/or grazed off. 

When terminating cover crops by grazing for vegetable production, you can graze off the cover very low to the soil surface, as long as you do not cause immense impact to the soil. If you want to direct seed a small-seeded crop, like arugula or spring mix, let chickens spend some extra time scratching down to the soil surface, or pigs to root around a bit, providing you some free bio-tillage and labor!

^{Photo by Zoe Schaeffer on Unsplash}

In the Orchard and on the Pasture

In an orchard or pasture, termination is not necessarily a management goal, because the vegetation species, or cover crop, should be managed accordingly to maximize their photosynthetic potential, proliferate, and ideally run their entire life cycle. We do not want to “kill off” our vegetation in a permanent system, such as an orchard. Instead, setting seed and adding to the latent seed bank is a goal of permanent vegetation management. 

When managing cover crops in orchards or pastures, I recommend taking a holistic and adaptive grazing or vegetation management approach. This includes allowing substantial aboveground biomass to maintain proper plant function and regrowth. If a cover crop is grazed too low—or mowed too low—the plant will stop photosynthesizing for many days, and eventually shut down, stop photosynthesizing completely and die, leaving the ground bare and unproductive.

In summary, do not graze or mow too low, allow good regrowth, rest, and recovery to occur before mowing or grazing a second time in the same season, and be sure you are always achieving good soil armor with residues, living roots, and diversity in your management.

^{Lush cover of grasses and vetch in a Northern New Mexico apple and grape orchard. Photo by Isabelle Jenniches CC BY 2.0}

The Importance of Grasses in Annual Vegetable Production

Grasses are the most powerful plant on the planet for building soil aggregation and rapidly restoring and improving soil health. But—the majority of vegetable species are brassicas, nightshades, cucurbits, umbel or carrots, and lettuce, or the Asteraceae family. The only grass species grown in a garden or on a vegetable farm is generally corn.

If you consider a typical growing season to begin in March and lasting until about November, that is 8-9 months of no grasses grown, and especially no cool season grasses. Not much if any grass is growing in gardens and fields during the actual growing season, and most farmers likely panic if grasses begin were to grow in the vegetable beds—we tend to call them weeds!

I bring up this topic as a final consideration, because increasing the length of time grasses persist in annual vegetable production is paramount to improved soil health. Spring cover crops provide this option—with of course the added benefit of other plant families—adding more diversity to the field.

No matter what approach you take or what your farm context is, the most important skill and least spoken about principle to master when managing cover crops, is the principle of “maximizing photosynthesis”.  Revisiting the six principles of soil health you will notice this principle is not written—however, you will realize if all principles are executed well, the photosynthetic potential of the land will increase.  One cannot master the soil health principles without an emphasis and deep commitment to maximizing the density and diversity of plants growing. It is photosynthesis that drives soil health, and the primary carbon pump which feeds the soil microbes, building soil organic matter, and ecosystem resiliency.  Enjoy your Spring Flowers!

This concludes our 3-part series on spring cover cropping. We hope you found it useful. Leave a comment or question below, we’d love to hear how your spring cover crop is coming along!

^{Happy cover crop seed recipient at the 2023 REGENERATE Conference. Photo by Isabelle Jenniches CC BY 2.0}