SHRINK YOUR LAWN WITH SHEET MULCHING! No shovel needed!

Sheet mulching is a fantastic - and quick - way to start a new garden packed with native plants! Sheet mulching can be used to convert a small (or large) turf-lawn areas into a tidy, blank canvas for creating a new flower bed or food garden. 

Sheet mulching can also be successfully used to build the soil profile of a site that is difficult to work with, has been degraded or that is very weedy. The incredible thing is that it is super easy to do (no digging!), uses up recyclable materials and makes excellent use of natural materials that you likely already have on hand!   

The method of sheet mulching is not new. It has been around for as long as people have been growing plants. Essentially, it is a method of smothering unwanted plants using layers of highly compostable, biodegradable materials. As the layered-up materials decompose, they leave behind an enriched soil that will provide fertile growing conditions for new crops. This also helps to kill off grasses and annual weeds (like Garlic Mustard, Alliaria petiolata) quite easily. In Southern Ontario, you may still need to keep a close lookout for Creeping Charlie, Glechoma hederacea, and Field Bindweed, Convolvulus arvensis. These are two difficult weeds that will likely find their way up through the sheet mulch but can be weakened by continual hand-pulling and the smothering of the sheet mulch layers (scroll down to find out more about invasive species and sheet mulching)!  

It can take around one full year, sometimes longer, for a sheet mulched area to decompose and be ready for planting food crops. However, when planting pollinator gardens using perennial wildflowers - like milkweed - trees and shrubs, you can plant into the sheet mulched area immediately if you want to! All you have to do is move the mulch aside, cut a hole into the cardboard, plant, then replace the sheet mulch layers and mulch. You can keep an eye around the base of the new plants to ensure that weeds do not find their way up through the opening in the cardboard before they are smothered.  

The Fungal Network

Perhaps one of the single most convincing arguments for sheet mulching, or "no-till" gardening, is in defense of the precious network at work beneath our feet. An entire universe of microorganisms are at work within the soil. We are only beginning to scratch the surface of understanding the intricacies and interdependent systems and cycles that make soil a living, breathing, moving entity. Our soils are often misunderstood, often overlooked and quite profoundly underappreciated.   

When you sheet mulch, you do not have to dig up and disturb the soil microorganisms that already exist in your gardens. Instead, you add so much fuel for them to continue to feast upon, increasing their reach and powers: powers which we are only beginning to understand. If you have ever pulled up a clump of soil and seen a network of ‘veins’ resembling a central nervous system of interconnected webs, you have seen the fungal network. Helping trees and plants to communicate with one another and possibly delegating, exchanging and managing carbon and other nutrients, the fungal network - or “the wood wide web” - is the life network of our soils.  

Texture and Tilth

An easy and highly effective way to improve soil quality in your gardens is to use leaf mould. In the autumn, leaves can be piled up into leaf compost heaps that will decompose into rich hummus which can be added back onto gardens. Or, you can even leave the leaves where they fall and where they blow, if your property is amenable to this. If you have lots of high-wind, you may need to contain the leaves if you want to try to compost them. This is similar to the nutrient-rich, robust, micro-organism rich soil that you would find on the forest floor.  

As leaves (and other organic matter) decompose, they produce organic acids, like humic acid, which improves a soil’s ability to aggregate or ‘stick together’. With a high carbon content, humic acid feeds soil microbes and makes it easier for a soil to hold onto nutrients that are needed for plant growth, instead of seeing them leach away. This is called the “cation exchange capacity” or CEC of a soil. For more information about the CEC, you can watch “Cation Exchange” (minus the ending spiel about chemical fertilizers that are unnecessary in a sustainable ecologically-planned and supported garden!). 

The Soil Microbiome

Gardeners should always compost the biomass from their own property - tree leaves, vegetable garden remains, grass clippings, plant cuttings - instead of letting it be hauled away in leaf and yard waste bags. Some may argue that this spreads plant pathogens from year to year. However, when you build a strong, biodiverse garden with lots of plants and insect life, these types of pest problems tend to find ways to balance themselves out naturally. 

Pesticides and herbicides become unnecessary in a garden where predatory insects make their home. For example, there are so many different insects that will prey on aphids (i.e. predatory wasps, lacewing and hoverfly larvae, lady beetles to name a few!). Planting native plants, like milkweed species, is a great way to attract these species! If you remove the biomass of the plants (fallen leaves and spent perennial stems and leaves), you remove habitat of overwintering species and microbial life. You end up robbing the system of a lot of its opportunity to take care of itself by cycling important nutrients and microorganisms back into the site. 

Leaf mould is also excellent for improving soils’ tilth which refers to its ability to both percolate and hold water, to hold its shape without compacting and to be friendly for root growth (with good aeration) and nutrient absorption.  Additionally, leaf mould is rich in microorganisms! We are just starting to understand the complex interrelationships between soil life and plants, but we do know that soils that harbour lots of micro-lifeforms are healthy soils! 

Soil microorganisms work to decompose organic matter into nutrients that plants can use, as well as helping plants to communicate with one another. Leaf mould is one type of compost that is used to inoculate soil (much like how humans can take a probiotic supplement to inoculate the digestive system with beneficial microorganisms). “How your fallen leaves can be used to fight climate change” is an article from CBC News, written in November 2021, which discusses the immense fungal network that is present in leaf mould. 

Leaf mould is highly effective for:  

• inoculating degraded soils
• increasing yields 
• increasing carbon stores (study in Arizona showed soil carbon increased by about 10 tonnes per acre in just one year)
• improving soil water storage and decreasing irrigation needs 
• improving the resilience of soils as self-sustaining systems   

Plus, the application rate is only 2 kg per hectare as opposed to regular compost which is applied at a rate of tonnes per acre!!! (1 hectare = 2.47 acres) 

For further reading, check out:

Suzanne Simard, “How Trees Talk to Each Other” https://www.ted.com/talks/suzanne_simard_how_trees_talk_to_each_other/transcript?language=en  

To learn more about mycorrhizae, watch “The Earth’s Internet: How Fungi Help Plants Communicate.” https://www.youtube.com/watch?v=_tjt8WT5mRs  

National Forest Foundation. 2021. Underground Networking: The Amazing Connections Beneath Your Feet. https://www.nationalforests.org/blog/underground-mycorrhizal-network 

Miller, Robyn. (2021). “How Your Fallen Leaves Can Be Used to Fight Climate Change.” https://www.cbc.ca/news/canada/ottawa/how-fungal-dominant-compost-can-heal-soil-protect-environment-1.6237228   

Sheet mulching can be a highly effective way to get the upper-hand on controlling invasive species at your site. It helps to smother weedy plants and weaken those that still manage to find their way to the surface. 

Field Bindweed, Convolvulus arvensis, for example, can have roots that reach more than ten feet underground. It is resistant to many chemical herbicides and nearly impossible to remove mechanically. Even if you manage to dig down to extract all the roots (which would be incredibly difficult to do) any small broken pieces of rhizome will regrow anyway. Sheet mulching deprives undesirable species, like Bindweed, of light and energy, while allowing native plants a chance to establish a strong foothold with less competition. 

Once invasive species do re-surface (yes, they always do), they are easier to control because they have likely used up a great amount of their reserved energy. After pulling the re-surfacing weeds a few times they will become very weak and may no longer be able to compete with the native plant community that has had a good chance to establish.  

With a species like Garlic Mustard, Alliaria petiolata, the biennial life cycle of the plant will be interrupted by the solarization process and the new seed bank in the soil will not have a chance to germinate. It is possible to eradicate garlic mustard from a large area in this manner. For further reading about invasive plants in Ontario, please visit the Ontario Invasive Plant Council, especially the “Resources” section. 

Monitoring your site on an ongoing basis and weeding as needed is still important to keep undesireable species from establishing or re-emerging.