Sheet Mulch: Creating Rich Soil Without Tilling
Have you ever dug a hole on a summer day in clay soil? The sun bakes your back as you strike your shovel to the ground. It seems like instead of the shovel digging the soil and soil is breaking your shovel.
Where I garden in the San Fernando Valley, we have lots of clay soil. These soils hold water and nutrients better than sandy soils. However, during our hot summers, clay soil bakes and trying to work it can turn anyone off of gardening.
I practice “no till” gardening as part of regenerative gardening. But, when you are creating a garden where there was not one before it is necessary to loosen the soil and work in nutrients. You may be familiar with John Jevons method of “double digging.” This works well but is a lot of work.
Sheet mulching, also known as lasagne mulching, is a method that creates rich garden soil without any of the hard work of tilling the earth. There is a significant amount of up-front work, mostly in collecting the materials. Once you have built your sheet mulch however, you can maintain it year after year with minimal effort.
What is Sheet Mulching?
Sheet mulching is basically composting in place. You create garden soil by layering carbon and nitrogen sources on top of each-other, keeping it moist, and letting it break down. It also improves the native soil underneath your pile as worms and other organisms move between your sheet mulch and the native soil, loosening it and transporting nutrients.
I originally learned sheet mulching from my favorite book on home-scale permaculture, Gaia’s Garden by Toby Hemenway. Hemenway includes a recipe for sheet mulching in his book that I have worked to simplify for backyard gardeners. I highly recommend his book for details on sheet mulching and other ecological gardening methods.
How to Sheet Mulch
Step 1: Gather Materials
The amount of space you plan to cover will dictate how much materials you will need. Rather than trying to cover a large area, start with a small space that you can do really well, then move on to the next space.
A great part about sheet mulching is that most of the materials are free and can be diverted from the waste stream.
The materials that I list are flexible. Ultimately, use what you have access to, there is not one right way to do this. The main idea is that we are alternating carbon and nitrogen materials. If you are unfamiliar with carbon and nitrogen materials take a look at my post, Compost: The Quick and Dirty Way.
Materials that you can use include:
- Cardboard/newspaper as a weed barrier
- Carbon materials: straw, dry leaves
- Nitrogen materials: compost, best manure for garden use – Healthy animals only (horse, cow, chicken, rabbit, sheep, goat, bat). Never use human, dog or cat manure. When using manure make sure the animals have not been given any antibiotics (we are trying to breed bacteria not kill them)
- Top soil
Step 2: Mow or string trim any weeds/grass
Cut down any existing weeds or grass as low as possible. No need to rake up the fallen material, it will decompose in place.
Step 3: Water
Wet the existing ground deeply. You will be watering heavily throughout this entire process. It is difficult to initially soak your sheet mulch but once it is soaked through it will retain water very well. If you are able to do this during a rainy time even better.
Step 4: ½ – 1 inch nitrogen layer
This layer will start attracting beneficial organisms to your pile and add a deep layer of nutrients that will encourage the roots to grow deep. Water.
Step 5: Weed barrier
Layer cardboard or newspaper at least ½ inch thick. This layer will help to suppress weeds by blocking out their sunlight. If you have a persistent weed like Bermuda grass, overlap the cardboard by one foot or more. Worms love cardboard and will find their way to yours and leave you rich worm castings. Water.
Step 6: 3 inch nitrogen layer
Find a source of free animal manure (I use horse manure because I have a good source). Many farms have to pay to have this taken away to a dump so they are more than happy to give it away for free. Water.
Step 7: 8 – 12 inch mulch
This is the thickest layer of your pile but will break down quickly. I use straw but dry leaves work equally as well. Water.
Step 8: 1 inch layer of compost or manure
For this layer you can use more manure, homemade compost or store bought compost. If I am doing a small garden I use Malibu Biodynamic Compost. It is pricey but it is the best compost you can find commercially. Water.
Step 9: 1 – 2 inches of garden soil
This will be the layer that you will plant into. Any organic good quality garden soil will work. Water.
Step 10: 2 inches of mulch
This is the final layer! Use dry leaves or straw. Water.
Step 11: Plant
You can now pull back the mulch and plant directly into the soil layer. You can start with whichever plants are appropriate to the season you are in. I like to start with a cover crop. These plants will add more nutrients to the soil and help to break down the pile.
The pile will be large at first but will quickly break down to only a few inches high. If watered adequately from the start the pile will also retain water very efficiently. There will also be plenty of nutrients to maintain several seasons of growing but I still recommend adding another 1 inch of compost and another 1 – 2 inches of mulch between each planting.
Sheet mulching builds rich, biodiverse soil. By focusing first on the soil, we ensure healthy plants in the future. By using materials that are often thrown away we lighten the load on the landfills and save money. This is a great weekend project to do with a few friends.