NO-TILL AND SHEET MULCHING
Information from Healthy Soils Workshop Series at Codman Farm
This is a summary of what we shared in our workshops, and is based on research we found in the resources we have listed at the end of this document. We encourage you to pursue these additional resources and keep learning.
NO-TILL GARDENING IS A MAJOR SHIFT FROM TRADITIONAL GARDENING, WITH MANY BENEFITS FOR SOIL HEALTH
WHAT IS NO-TILL GARDENING?
Traditional gardening starts with tilling: turning over the soil and breaking it up. In
no-till gardening, the goals are to maintain soil structure and keep the soil covered. The soil can be covered by crops, cover crops, mulch, or some sort of sheet covering. Mulch can be things like compost, manure, straw, wood chips, or dead leaves. A sheet covering can be cardboard, fabric, or plastic. Cardboard is probably the best choice, especially for smaller gardens, because you can leave it in place and it will decompose to become part of the soil.
In no-till gardening, plant roots are left in the soil (unless you have a crop like carrots where you are harvesting the roots). You cut off the plants at the end of the season at the soil surface, and the decaying roots become part of the carbon-rich soil organic matter.
One reason people till is to kill weeds, but actually, while it kills weeds at the surface, it also brings weeds to the surface where they are able to germinate.
Though it takes some getting used to and may require a couple new tools, particularly for smaller gardens, no-till is cost effective and hugely beneficial for soil health and soil carbon storage.
NO-TILL IMPROVES SOIL HEALTH AND STORES CARBON IN SOIL
No-till is an important technique for regenerative agriculture, restoring soil health
and also increasing carbon storage in soil. Soils, which are already vast global carbon stores, have the potential to store more carbon. That is because historically we have done things like tilling and other intensive practices that disturb soil and cause carbon loss. To store more carbon in soil, we both need to add more carbon to the soil, as you will or have discussed at the station on native perennials, but we also need to keep the carbon that is in soil in there! Soils can store carbon for thousands of years, helping keep it out of the atmosphere. But when soils are disturbed by practices like tilling, carbon is released to the atmosphere. There are two major reasons tilling causes carbon loss from soil: it breaks apart soil aggregates (which we will define in a moment) and it causes lower soil microbial diversity. Microbes are key to soil carbon storage, and the more diverse and abundant the soil microbial community, generally the more carbon that gets stored.
Soil structure describes how individual particles of sand, silt, and clay are
assembled. When individual particles are assembled, they look like larger particles, which are called “Aggregates”. These aggregates can have different shapes and patterns, which cause the soil to have different structures. Soil structure strongly influences movement of water through the soil. It can also influence things like the ability of the soil to retain nutrients and even the composition of the microbial community in the soil. A healthy soil has lots of aggregates with networks of pores in between. Aggregates protect soil organic matter from decomposition - this is very important for helping store more carbon in soils. They also help with water flow through soils. They help give the soil a structure that makes it easier for roots to grow (more connected pore space). And they help minimize erosion.
No-till preserves soil aggregates and helps maintain an abundant and diverse microbial community. Soil microbes improve plant growth, providing services to the plant like nutrient acquisition and protection from pathogens. A large portion of persistent carbon in soil; carbon that sticks around for a long time; is actually dead microbial bodies, or necromass. More microbes in soil can lead to more stored carbon.
Sheet mulching is a method of no-till gardening. Sheet mulching not only requires no tilling, but also adds carbon-rich organic matter to the soil. Sometimes sheet mulching is called lasagna mulching because, like a lasagna, you are building up layers. With sheet mulching, those layers may consist of cardboard, compost or another nitrogen-rich organic material, "brown" material such as dried grass or leaves, and/or mulch such as straw or wood chips.
Sheet mulching can be used for vegetable gardens, ornamental garden beds, or for converting lawn to meadow or garden. You can even sheet mulch directly on top of grass or weeds.
If you are sheet mulching in the fall, over winter, the layers of organic material will begin to decompose, providing a perfect base for planting in the spring, though a layer of soil or compost above is usually needed before planting. If you are sheet mulching in the spring, you may need more soil or compost on top before planting, and it can help to cut small holes into the cardboard for plants.
Members of the Lincoln Garden Club have started engaging with no-till gardening and are a great resource: https://www.lincolngardenclub.org/
Codman Community Farm is doing no-till and conservation till: https://codmancommunityfarms.org/
US Department of Agriculture information: https://www.usda.gov/media/blog/2017/11/30/saving-money-time-and-soil-economics-no-till-farming
Rodale Institute information:
A great, general guide to soil health and management, but not no-till specific:
SARE’s archive list of no-till reading:
K. Paustain, E. Larson, J. Kent, E. Marx and A. Swan. "Soil C Sequestration as a biological negative emission strategy." Frontiers in Climate 16, 2019, doi:10.3389/fclim.2019.00008.
J. Sanderman, T. Hengl, and Gregory J. Fiske. "Soil carbon debt of 12,000 years of human land use." Proceedings of the National Academy of Sciences 114 (36) 9575-9580, 2017, doi:10.1073/pnas.1706103114.
D.A. Bassio, S.C. Cook-Patton, P.W. Ellis, J. Fargione, J. Sanderman, et al. 2020. "The role of soil carbon in natural climate solutions." Nature Sustainability 3, 391–398, 2020, doi:10.1038/s41893-020-0491-z