Sheet Mulching for Pleasure and Profit

Welcome, soil nerds and flower friends! In this post, I’ll be showing you step by step how I prepare planting beds here at Sea Change Farm.

What is Sheet Mulching?

Sheet mulching is a layered mulching technique that suppresses weeds and builds the soil. It mimics the natural soil-building process in a forest, where layers of fallen material decompose and build up a rich understory.

Sheet mulching is a no-till growing method. No-till growing aims to disturb the soil as little as possible. Reducing tillage helps to preserve soil structure and encourage healthy communities of insects and microbes.

I first learned about no-till growing during a soil health class I took online through Cornell University. For more information about no-till and why it’s good for our soil, I recommend this podcast and this book.

My sheet mulching method requires only a shovel, a wheelbarrow, and a boxcutter–no expensive tractor needed! Sheet mulching can also be performed whatever the weather, on top of dry, wet, rocky, compacted, or even frozen soil.

My Method

My sheet mulching method is informed by trials I did this spring, various podcasts and articles I’ve consumed, and the natural materials I have on-hand.

The more I read about different no-till systems, the more I’m convinced that there is no single Right Way® to prepare a no-till planting bed. I hope that you can use my method as inspiration for finding the best solution for your own growing space.

Without further ado, here are the steps I follow when sheet mulching a planting bed at Sea Change:

1) Plant Massacre

The goal here is to remove the previous crop from the planting bed while leaving its roots intact. The plant roots will feed microorganisms and preserve soil structure as they decompose in-place.

I go through and cut all the plants off at the base. For a soft-stemmed or low-growing crop, you could skip this step and go directly over it with cardboard in step 3.

This is one of the most time consuming steps for me since I do it by hand with clippers, or sometimes with a scythe. I’m still looking for the right tool to help me do this more efficiently. A string cutter with blade attachments or a well-sized mower might work well here.

Pile the dead plant matter nearby for step 4. If there are other things on the bed, like drip lines or landscape fabric, remove them now.

2) Amendments

If you want to add amendments to the soil besides compost, this is the time! My soil is a bit acidic and low in calcium, so I add a sprinkling of calcitic lime.

An extra step I’ve been considering is to broadfork the bed at this point. If you are dealing with compacted soil, consider broadforking at this point. If you do broadfork, I would try also adding compost before the cardboard goes on to stimulate some more microbial activity in your newly-aerated bed.

3) Cardboard

For this, we want plain brown cardboard, the bigger the better, opened up so it can lie flat in a single layer. Printing with blank ink is usually ok. If you are certified organic, other colors of ink may not be ok for you to use (I use them). If the cardboard has a shiny printed finish it is no good.

Apart from plasticky finishes, plain brown cardboard seems to not contain any toxic materials that are detrimental to soil activity. In fact, it attracts earthworms like crazy! I’ve read that the glue in most cardboard is made from animal hide, and earthworms like it for its high protein content.

Prep your cardboard by removing any tape, labels, and metal staples. You could also leave these things in if you can’t be bothered, but you will find them later in your soil.

Now is the most satisfying part! It gets more satisfying the bigger the cardboard. Lay your sheets down to cover the bed. Overlap adjacent pieces of cardboard by a few inches for better weed control.

Since I’m prepping new land, I also cover the pathways on either side of the bed with cardboard, but in future years I probably won’t do this.

If you are sheet mulching on a windy day, alternating between this step and the next step will keep you from chasing cardboard sheets all over the place. If you plan to plant directly into your bed after making it, wet the cardboard with a hose. This will help it break down more quickly.

4) Organic Matter

With the cardboard down it’s time to start adding organic matter. Some sheet mulchers add organic matter below their cardboard rather than on top of it. I prefer putting the organic matter on top, so my sheet mulch beds are ready to plant into as soon as I finish building them. If you use the cardboard as a top-layer mulch, you’ll have to cut holes through it to transplant. For flowers, which are grown very densely, this sounds like a huge pain to me.

The first layer of organic matter that I add are the dead plants I chopped off the bed in step 1. Cut these up or step on them a bit so they lie flat-ish over the cardboard.

If you don’t want to use the previous crop as a layer, you can skip it. You can also use other plant matter, such as fallen leaves, straw, woodchips, or lawn trimmings. If you’re prepping beds in the fall, you could add food scraps now, since they will have lots of time to break down.

5) Compost

The good stuff! Add enough compost onto the bed to cover the dead plants that you added in step 4. At the end of this step I aim for my bed to be 3-4″ high above the cardboard.

I’ve heard it said time and time again to buy the highest quality compost that you can afford. I must admit, the compost I sourced this year isn’t the highest quality. I’m adding such large quantities of compost to my beds that it would blow my budget to pay an extra $25 per cubic yard for better compost. But hey, organic matter is organic matter! I feel confident that my beds will be ok.

6) Top-layer Mulch

Some no-till growers treat compost itself as a mulch layer. This can be a great approach! I’m topping off my beds with a layer of straw, though. While the compost does help suppress weeds, I think of my compost layer as next year’s soil rather than a mulch.

The benefits of mulch are many. Mulch encourages life in the soil beneath it by providing shelter and preserving moisture. I’m attempting to draw microbial and insect life up through the entire compost layer, so I cover it.

If straw isn’t readily available, use another mulch material such as fallen leaves or even landscape fabric.

7) Pathways

I missed this step in the spring, and I had a horrible time with annual and perennial weeds because of it. Mulching the pathways is a game changer. Now, I mulch them heavily with woodchips over cardboard.

I’ve heard contrasting opinions about using woodchips in the garden, but I was encouraged to try using them by Charles Dowding’s interview on the No-Till Market Garden Podcast. Charles Dowding is a bit of a no-till farming celebrity with decades of experience growing this way, and if he uses woodchips, they can’t be all that bad.

Because they take a long time to break down, some say woodchips lock up nitrogen in the soil, “stealing” it from your plants. While I can’t say definitively whether this is happening at my farm, I observed no adverse affects on the neighboring plants when I mulched my pathways with woodchips.

Why Woodchips?

Woodchips offer me a few huge advantages. Woodchips, when they aren’t treated, often already host fungal communities. Ever turned some rotting wood over to see white stringy stuff on the bottom? Fungal networks! There is compelling evidence that fungal networks can form beneficial relationships with plants, supplying the plants with nutrients and allowing plants to share nutrients with each other. I am excited to encourage this on my farm.

Woodchips have been my best mulch for stopping perennial weeds. These weeds, like bittersweet and virginia creeper, eventually still come up through the woodchips, but they come up in a weakened state that makes them easy to yank out. It seems like the woodchips are also a more difficult medium for weeds that spread out laterally through runners.

Rotting wood can store of water, which is another reason I like woodchips. This is a note I’ve taken from reading about hugelkultur as well as the podcast listed above; Dowding says on his farm, the plants nearest the woodchipp-ed pathways are the healthiest, and he thinks it’s because of the extra water they hold.

Best of all, the woodchips were free for me! Depending on your area, arborists are often happy to have a place to dump woodchips from their jobs without paying for their disposal. This is a good chance to practice your cold calling skills 😉

8) Admire / Plant

That’s it! Your sheet mulched bed is done. Unless your compost is full of fresh manure or you added food scraps to your bed, you can plant directly into it. Or, let it sit to improve with age.

Where to source cardboard

I’ve sourced cardboard from a few places, including a local coffee shop and an appliance store, but my best cardboard hookup is my local recycling center. My transfer station is staffed by really friendly people who set aside cardboard for me each week. They know I like large sheets with no printing on them, and they save me the good stuff. Shout out to you, Bob!

If you have a furniture or appliance store near you, that’s a great option. However, my local appliance store has a strict workflow where they compact their cardboard down and it gets picked up by a third party. Setting aside boxes for me doesn’t fit into this flow, so I have trouble sourcing from them.

If there’s one I’ve gotten better at this year, it’s cold calling local businesses! Whether I’m trying to find new places to carry my flowers or trying to source castoff materials, my phone is my best asset. You, too, can set aside your social anxiety and ask for leftover cardboard.

Go Forth and Sheet Mulch

I hope my sheet mulching method is helpful to you! Again, I don’t think there’s a Right Way or a Wrong Way to do this. If you use a similar method on your farm, or a very different one, I would love to hear about it.

Samantha is the farmer and owner at Sea Change.

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