Regenerative farmers and gardeners aim to keep the soil planted as much as possible.
Whether planted with vegetables, perennials, or cover crops, the more plants are in the soil, the more photosynthesis happens. Photosynthesis supports soil microbes, and sequesters carbon at the same time.
But, once it’s time to swap out a crop or terminate the cover crop, those roots aren’t done with the ways that they can benefit the garden.
This leads to the regenerative practice of keeping roots in the ground whenever possible.
In this article, we’ll explore why regenerative gardeners leave roots in the ground and how it benefits carbon sequestration and soil health. We’ll also look at when it’s not practical or a good idea to leave roots of plants in the ground.
In general, regenerative gardeners strive to keep roots in the ground as much as possible.
This is practiced in two ways:
First, we keep the soil planted as much as possible with living plants.
Second, when annual plants are done for the season, we cut them back at the base so the roots are left behind.
Let’s look at the benefits that living roots in the ground have first. Understanding this will help us to understand why we retain roots after the plant is finished growing.
Thriving Soil Microbiome
If there are no living roots in the ground, the soil microbiome goes dormant. According to the University of Wisconsin-Madison, this means that when spring comes and the soil is planted, it takes some time for the microbes to come back up to speed.
Carbon Sequestration
While it’s the leaves of the plant that make photosynthesis possible (in most instances), the roots need the carbon that is drawn down from the atmosphere during photosynthesis in order to grow.
According to Jane Callier, a Master Gardener from the University of California, this is one way that carbon gets sequestered into the soil. In her article, she shares that mycorrhizal fungi form a relationship with most plant roots to sequester more carbon.
To quote Jane: “Mycorrhizae metabolize more root sugar, plants grow, pull down more carbon from the atmosphere, and roots transfer minerals absorbed from the soil into the plant. Both plants and soil structures benefit from the interaction.”
Dr. Vijayalaxmi Kinhal, forest ecologist, notes that living roots are a big part of soil carbon absorption: “Roots comprise 20-25% of plant biomass but contribute 75% of carbon from plants to soils.”
Soil Structure Improvement
Callier goes on to explain how plants, roots, and microorganisms improve soil structure. The mycelium in the soil create a substance called glomalin, which supports soil connectivity. When soil is able to “connect” with itself, it’s called aggregate. The aggregate prevents soil erosion and helps water to penetrate into the soil. As Callier says, “A healthy biome without aggregated soil cannot exist.”
One way to build aggregated soil? “The goal is to have roots in the ground year-round,” Callier says.
Nutrient Cycling
UWM details another benefit of roots in the soil: Other nutrients get delivered into the soil because of the relationship between the roots and soil microbes, especially nitrogen and phosphorus.
Biodiversity of plants is also reflected in the roots: different plants have different root formations and exudates. UWM shares that some plants have long roots which are able to bring minerals deep in the soil up to the surface for other plants to utilize. Other plants have sprawling roots that help prevent erosion and form aggregated soil.
As an added benefit, this study found that a diverse integrated planting system stores more soil organic carbon!
Legumes and other nitrogen-fixing plants store the nitrogen in small nodules on their roots.
Soil Aeration and Drainage
As roots grow downwards and outwards in the soil, they create space within the soil to allow for better tilth and drainage. This is especially helpful for those who live in areas prone to flooding. Soil aeration helps remediate and prevent compaction as well.
Additionally, the channels that living roots create during the rainy months guide the roots of the next crop through the soil. Don Donovan, district conservationist with the National Resources Conservation Service, explains that this benefits plants grown during hot and dry summer months are able to grow easier.
Erosion Control + Prevention
As we have seen modeled for us in the Dust Bowl, soil erosion can be detrimental to the land. Luckily, when at-risk land is planted with living herbaceous or perennial plants, soil erosion decreases.
This is because the roots hold the soil in place. The plants themselves help to slow down runoff speed during heavy rainfall, and the improved aeration provided by the roots helps with water absorption and drainage. The stable aggregates that were mentioned above also help prevent soil erosion.
When the plant has been cut back, the roots still have something to offer to the soil. These left over roots are sometimes called “root litter” in scientific literature.
Support for beneficial soil organisms, microbes, and insects
According to SARE, dead roots are a significant food group for microbes and insects alike. Even earthworms eat decaying roots.
Carbon Sequestration
This article from the Journal of Nutrient Management outlines how the death and decaying process of roots below ground is part of soil carbon storage. This is due to the formation of stable humus and allowing plant decomposition to occur in deeper layers of the soil. If we do not allow the plants roots to die back in the soil, we are missing an opportunity for carbon storage.
A research paper notes that part of why global soil carbon storage has decreased is because less plant roots and material are retained in the soil.
Less soil disturbance, less carbon released
A core tenet of regenerative gardening is “disturb the soil as little as possible.” This is because soil disturbance, from tilling to uprooting plants, causes soil carbon emissions.
Some soil disturbance is unavoidable if you are going to harvest potatoes, carrots, or other root crops.
However, we reduce the amount of soil disturbance in our garden when we leave the roots of above-ground crops in place when the season is complete.
Organic Matter
According to UMD Extension, when plant roots break down they improve the health of the soil and support soil microbes and fungi.
One type of organic matter formed by decomposing roots is humus, which is very stable on a molecular level. It can store and retain carbon for hundreds of years.
Additionally, this organic matter can help improve the soil texture of soils that lean towards clay or sand. Retaining roots helps your soil to become more loamy in structure over time.
More organic matter doesn’t only improve soil structure, it also helps soil to retain more water.
Continued Nutrient Cycling
Once dead roots break down fully, they expel any remaining nutrients not used by the plant. These nutrients will be available to any living plants or the next season’s crop.
If you pull up and discard a nitrogen-fixing plant, the nitrogen nodules that are present on the root of the plant are discarded too.
Before we look at how to leave roots behind, we need to look at the times when it is not appropriate or helpful to leave roots in place.
This strategy works best for raised beds and when rows are interplanted.
For this type of situation, you’ll need some good pruners. If the plant has a wide stem, loppers might be a better tool for the job.
Cut the plant back as close to the soil as possible. If you’re able to clip the plant a little below the soil, that is even better. This will help to prevent the plant from regrowing a little bit more. Drop the leaves in place and add some compost to the area before sowing new seeds or planting a new batch of seedlings.
To be honest, this is the method I tend to choose even for large plantings that need to be terminated. I feel like I can do a better job and see what I’m doing, even if it takes me a little longer.
This strategy works best for in-ground rows.
You’ll need a plank or t-post, and 2 pieces of rope or twine that is 1.5 times your height.
Tie the bottom of the rope or twine to either end of the plank or post. Stand with the t-post or plank the long ways on the ground so you can step on it with both feet. With the string, lift the board up and then press it down on the cover crop, stepping on it. Lift it up again, walk a step, and let the board drop. Step on it again. Keep going until all of the crop is “crimped” back.
If you have a week or two before you need to plant your next crop and it’s summer, a black tarp is another way to terminate a large planting without pulling up any roots.
Depending on the crop, the weight of the tarp might semi-crimp it for you, or you might need to do a preliminary chop of the plants at the base.
Cover the area with a black tarp, and secure the edges down with something heavy, like bricks.
If it’s not summer, this method will take a lot longer, but might still be worth it if you’re killing back weeds or an invasive patch of plants.
While the roots of the plants hold heaps of benefits for the soil, the above ground components of the plants have value too.
You can utilize the “chop and drop” method of syntropic gardening and permaculture. To do this, simply cut back the plant as outlined above, and let the above ground leaves and stems act as a mulch for the soil. If the plant has gone to seed, you may wish to remove the seeds if you don’t want the plant to repopulate itself.
You can also bring all of this rich plant material over to your compost bin to bulk it up. Don’t forget to turn your compost bin frequently to keep it aerobic and to help all the worms and microbes to break down the raw material.
When you leave some plants with hollow stems behind, these beneficial insects have a place to stay over winter.
As regenerative gardeners, we do a lot during the growing season to attract beneficial insects into our garden. It can be easy to forget that some of them need a place to stay over winter. But if you leave some plants in ground for them, you’ll have even more success in the next growing season with your wildlife populations.
Some folks may not like having the root of plants behind in the soil, because they fear these roots will get in the way of new plantings. They might also be frustrated if a persistent brassica decides to keep sprouting leaves if it wasn’t cut back deep enough.
While in some ways, it might seem like more work to keep your garden in this way with herbaceous annuals. But on the other hand, the benefits could contribute to less work needed in the garden in other ways. With improved soil aeration, organic matter, microbial life, and nutrient availability, the extra work is worth it for me.
On top of it all, each time I snip a plant back and leave the roots behind,I am contributing to carbon sequestration. And that’s a worthwhile cause to contribute to.
