With so many different methods of sheet mulching out there and with each method sometimes having contradictory information, it can be confusing and hard to know how to get started. So, in this guide, my aim is to break down the sheet mulching process into simple steps with clear explanations for each step.
Sheet Mulching Can Be Simple…
You can make sheet mulching as simple or complex as you like. The simplest method is to lay down cardboard and cover it with woodchips, anywhere from 4-12 inches thick, depending on your available resources, climate, and goals.
This basic method makes the most sense when you’re sheet mulching large areas, however, sourcing other materials in quantity, such as compost, might be difficult. This is what we did to start our food forest.
…or Sheet Mulching Can Be More Complex
For smaller beds and borders, where you want to grow intensively or quickly, it makes sense to add soil amendments and more organic materials to quickly improve the soil.
So here’s how to sheet mulch with more layers.
Easy Sheet Mulching Process
The pictures below show the process I went through to start a perennial bed on one corner of my garden (except for Steps 1 and 4, which are stock images, since I didn’t have to mow, and didn’t have worm castings or other amendments on hand).
I had previously sheet-mulched the area with cardboard and woodchips only, but I wanted to build a better bed for planting next spring. So, I raked the woodchips to the side and started fresh.
1. Mow Tall Grass and Weeds (If Applicable)
If your area has tall grass or weeds growing in it, pass over it with a lawnmower or weed wacker. Leave the clippings in place, either by using a mulching mower or spreading them out over the area after mowing. This tidies up the area and provides a good layer of organic material to start with.
An optional part of this step is to remove tenacious perennial weeds. This isn’t usually necessary, especially if you use a good weed barrier and mulch thickly. Leaving weeds in place but mowed is actually beneficial because they add organic matter to the soil when they decompose. However some very persistent weeds might survive and push through the cardboard and mulch and cause issues, so pull them up if you’re concerned about any specific weeds.
2. Loosen the Soil (Optional)
Loosen (but don’t turn) the soil with a pitchfork. This opens up the soil, allowing water and air in to activate and stimulate soil life. This gentle opening of the soil facilitates movement across the soil-mulch boundary without disrupting the delicate soil food web already present.
This step is optional but recommended if you’re working on top of already compacted soils.
3. Water
Give the ground a good soak with the garden hose. Water is a critical component of healthy soil. When the soil is dry, everything slows down. Microbial activity is reduced and decomposition slows. And once the other layers are in place it will be harder to wet through all of the layers. But if the ground is moist prior to sheet mulching, the thick mulch will hold in that moisture.
4. Add Soil Amendments (Optional)
Put down any soil amendments you’d like to use. Some good amendments to give your garden bed a boost of organic matter or trace nutrients are:
- worm castings (organic matter)
- compost tea (organic matter)
- rock dust (trace nutrients)
- kelp meal (trace nutrients)
A little goes a long way here, so choose one or two amendments to lightly sprinkle over the surface. There are plenty of products available to buy, or use what you have or can make.
If you’ve tested your soil for pH and nutrients, then you’ll probably have a list of recommended amendments to improve your soil.
If you’re interested in making your own garden amendments, an excellent resource is Nigel Palmer’s book, The Regenerative Grower’s Guide to Garden Amendments.
Step 5. Carbon Rich Layer, Weed Seeds are Okay (Optional)
Put down a layer of carbon-rich (brown) organic material, such as hay, straw, aged grass clippings, or fall leaves. It’s okay if the material contains weed seeds because it will be beneath the weed barrier. Any seed that germinates will be smothered.
Although this layer is optional, don’t skip it if you’re including the next layer, nitrogen-rich materials. This is important in order to balance the carbon-to-nitrogen (C:N) ratio. So if you are including nitrogen-rich material, then add some brown organic matter for this step, even if you have to use weed-free materials.
Step 6. Nitrogen Rich Layer, Weed Seeds are Okay (Optional)
Add nitrogen-rich (green) organic materials. Fresh grass clippings, manure, aged manure, kitchen compost, and even uncomposted fruit and vegetable scraps from the kitchen are suitable here. If you include this layer, also include the previous layer (Step 5) of carbon-rich materials directly beneath it.
If you want to generate more compost for use in sheet mulching–there never seems to be enough compost–then read my post on urban composting methods.
Kitchen scraps might not have weed seeds, but if you’re using uncomposted scraps, they should be buried as low in the layers as possible to avoid attracting pests. Another benefit of including this layer of nitrogen-rich organic material below the weed barrier is that it will attract earthworms and other decomposers, which are of course excellent for garden soil!
Step 7. Water (Again)
Give the bed a good watering. It’s good to water well between layers, particularly when the materials are dry. Once the weed barrier goes on, water won’t infiltrate as well into the lower layers. So, use this opportunity to soak it well.
Step 8. Weed Barrier
Put down a weed barrier that will decompose over time. The best material for this is cardboard, but several layers of newspaper or other paper will also work.
Peel off any tape and labels that may be on the cardboard, and pull out any staples. Soaking the cardboard in water first can make pulling off stubborn tape much easier. It’s also a good idea to moisten the cardboard to prevent dry spots in your sheet mulch layers, so either pre-soak it or put the sprinkler on it for a few minutes after it’s laid out.
If there are any existing plants in the garden bed that you want to keep, cut the cardboard out around them, and make sure that the compost and mulch layers below aren’t burying the stems. Give plants a good four to six-inch radius of clear space between their stems and the mulch.
Step 9. Compost or Soil, Weed-Free (Optional)
Put down more organic material, but this time make sure it is weed-free. The best and simplest material to use here is properly finished compost. You can also mix in vermiculite or sand to improve drainage. If you don’t have compost, you can use commercially prepared garden soil or compost. Many nurseries will deliver compost and soil by the cubic yard.
Step 10. Mulch, Weed-Free
Finally, lay down a thick layer of mulch, about four to six inches, and at least three inches deep. For perennial garden beds, arborist’s woodchips work very well. For annual beds, it’s better to use finer-grained wood chips or weed-free straw.
Step 11. Water (and Again)
The very last step is, you guessed it, watering the entire bed again. After watering, leave the bed alone to do its own thing over the winter (if you’ve started in in fall or winter). If you notice the bed getting dry, water it from time to time. If you get snow in your area, pile the snow onto the bed to insulate and keep it moist.
Remember to do your best to avoid stepping on sheet mulched areas, as walking on them compacts the soil.
Planting into a Sheet Mulched Bed
Although it’s best to let a new sheet mulched bed age for a few months, it is possible to plant in it right away. Any time you’re ready to plant into the bed, follow these steps:
- Rake back the mulch from the area you’re going to plant in, a little bit wider than the planting hole will be.
- Remove soil and compost to expose the cardboard (if it hasn’t had time to decompose yet). You can shovel soil into a wheelbarrow or onto a tarp or sheet of cardboard temporarily—just to keep it from getting mixed in with the mulch.
- Cut away the cardboard in a circle the same diameter as your planting hole will be, or simply cut an “X” in it to allow plant roots a way through. Fold the corners back to access the soil for digging.
- Dig a hole as deep and wide as it needs to be for your plant. This should be three times the width of the root ball and about as deep as the root ball is tall.
- Situate your plant in the hole to get it to the right height. The level of potting soil should match the new soil level. For simple sheet mulched areas (cardboard and mulch only) this will be the original soil level. For the beds you have added soil to, this will be the top of the new soil level (From step 9 above).
- Backfill the soil around the plant and gently firm it in place with the palm of your hand.
- Water in your plant to help settle the soil and give it a good drink.
And That’s How Sheet Mulching Is Done!
This is my method of sheet mulching. It’s an amalgam of several different methods I’ve seen in books and videos, including Rosemary Morrow, Morag Gamble, Geoff Lawton, and Eric Toensmeier. Remember that your own sheet mulching method can differ from mine depending on your own resources and desires for your garden.
At its simplest, sheet mulching is just a weed barrier and mulch. Adding compost and soil amendments will build your soil more quickly, and fill in gaps in the nutrient profile of your garden soil.
I hope the simple process I‘ve laid out is helpful. If so, put on your gardening gloves, gather your tools, and get sheet mulching!
If you found this article helpful, you might also like How to Make a No-Dig Garden: Fertile Soil, Less Work.
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