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The regenerative urban garden II: Sheet mulching

This is the second in a series of posts about regenerative gardening techniques. Read Part I on No-till here!

If you’ve heard of permaculture, you’ve probably heard of sheet mulching. Sometimes it feels like the two are treated almost as synonyms: every Permaculture Design Course must include the initiation rite that involves laying down cardboard as earnestly as if you were trying to cover the entire planet in it. Every self-respecting permaculturist will be spreading cardboard… I mean, the gospel of sheet mulching, wherever, whenever.

I’m being just a tad sarcastic. Sheet mulching is hands down one of my favorite and most effective methods of garden establishment and soil-building. I’ve done a lot of it myself, made some mistakes in the process, and almost gotten into trouble for pulling cardboard out of the dumpsters behind Target. I think sheet mulching is an essential tool in the toolkit of regenerative gardening. But just to be clear: I don’t think it’s always the right choice, and it’s not bulletproof.

What is Sheet Mulching?

Sheet mulching means laying down layers of organic material, including a weed block layer of some kind (usually cardboard or old newspaper), to smother existing plants and create a blank canvas, if you will, on which to establish a new garden area. Some people call it “lasagna gardening” — the same idea.

Here are the main benefits of sheet mulching: It

  • acts as a great weed block (if done right), giving you and the plants you choose to plant a competitive edge over weeds
  • takes materials out of the waste stream (such as newspaper or cardboard) and converts it into garden soil
  • is a great soil builder! The layers of organic materials gradually break down and get incorporated into the soil. Earthworms and other critters crawl up to munch on them, aerating the soil. The whole process builds the humus layer.
  • …and that is why sheet mulching is a regenerative and carbon-sequestering gardening practice, especially when combined with cover crops. It provides soil cover; it feeds the diversity of biology in the soil; and it has the potential of turning carbon-rich organic materials like straw or cardboard into the kind of carbon that feeds the living soil.

Since Toby Hemenway has written a killer how-to for sheet mulching, I don’t need to go over all the steps here. Instead, I’m going to share the sheet mulching process we’ve done as part of establishing our urban homestead in the past year, and some lessons learned.

Here’s our front yard a few weeks after we moved in in Spring 2018:

Our goal was simply to build soil in this area for a year before planting anything (in contrast to the vegetable beds that you see me double-digging in the background in this photo). Having the blank canvas of the sheet mulch also allowed some design ideas to come forth.

Once the last layer was on, I seeded the entire area with a cover crop mix. And here’s what the area looked like about three months later:

In other words, the cover crops took off. They pushed their roots through whatever layers of cardboard remained, pumped lots of nitrogen into the soil, and grew flowers that attracted pollinators. The Nitro radish in Sow True Seed’s cover crop mix busted through the compacted soil with its thick tubers and such vigor that it drew many remarks from neighbors and passers-by.

The one challenge, I’d say, with using a cover crop mix with multiple plant species in it is that it became challenging to monitor for the weeds that inevitably did push their way through the cracks of the cardboard layer. By the fall, I was happy with how the cover crop was working the soil, but also finding a lot of pernicious vines and weeds.

For that reason, we scythed it all down in the fall, and in the spring, we did it all over again.

This time, we used thinner rolls of brown paper instead of cardboard, laid out pathways with woodchips to create the teardrop shape for this future mini forest garden, and started planting perennials. I’m really happy we did two rounds of sheet mulching, even though it was a lot of work. Now when I put my hand into that soil, I see a new dark brown layer over the lighter, clayey original soil, and the soil’s got great texture and fluff to it. That’s what we’re going for.

 

Top recommendations and lessons learned:

  • Do smaller areas at a time. It’s a lot of work, wheelbarrowing all that organic material, and you’ll tire yourself out if you try to do too much at once.
  • If using cardboard, find the biggest pieces of cardboard you possibly can. Bike shops, kayak and canoe shops, furniture and home appliance stores usually have huge boxes in their dumpsters they don’t mind you hauling away.
  • An alternative to cardboard are rolls of brown paper (sold in the painting section at Lowe’s or Home Depot, for example). You’ll want to do at least two layers, but don’t need to spend time pulling out tape and staples from cardboard.
  • Make it a work party! Sheet mulching is overwhelming if done with too few pairs of hands, but a riot if you invite your friends.
  • Water the soil well before starting, and keep watering the weed block layer as you go. The soil-building organisms that will be munching on your sheet mulch cake need moisture to do their thing.
  • If cover-cropping, a single species cover crop seed might be a good idea, for reasons explained above
  • Plant any large perennials first and sheet mulch around them, rather than trying to cut into the cardboard and then dig a planting hole. Again, I speak from experience.

 

 

The regenerative urban garden I: No-till gardening

I am an advocate of regenerative farming. But I am not a farmer myself. The piece of land I steward is 1/3 acre — still sizable for an urban lot, but laughably minuscule compared to what Real Farmers are working with.

Yet, when I landed here last year and set out to establish our gardens, I decided I’d try my best to apply the same principles that regenerative farmers use when working the land. The benefits of regenerative farming practices add up to something pretty phenomenal: improved soil health, improved ecosystem health, better water retention, less erosion, more carbon sequestered in the soil… and more nutrient-dense food as a result.

Why would I not want all those benefits in my own garden, too? What would regenerative gardening, or carbon gardening, look like?

This post series is my attempt to answer that question. (Mind you, this is only our second year of gardening on this land, so no doubt I have a lot yet to learn and some steep learning curves to climb.)

 

Regenerative growing practices on the urban backyard scale

Here’s my back-of-the-napkin, off-the-cuff summary of key regenerative land management principles:

  • Disturb the soil as little as possible.
  • Always keep the soil covered.
  • Always keep a living root in the soil.
  • Plant more perennial crops.
  • Diversity, diversity, diversity!
  • Incorporate animals into the system, and have a system in place for rotating them through landscape.

Now, all of these can absolutely be applied even on the urban or suburban garden scale. Soil is soil is soil. There’s nothing inherent about them that says you can only do them if you have 200 acres to manage.

Let’s start with the first one. The way to disturb the soil as little as possible translates to:

 

no-till (or no-dig) gardening

No-till is exactly what it sounds like: you farm, or garden without ever tilling the soil. Tilling and plowing are almost synonymous with land cultivation, aren’t they? Yet they actually destroy soil structure, create compaction, and kill the very soil biology that’s the basis of fertility, like fungal networks and all those earthworms that make the soil nice and squishy.

But if you don’t till, how, then, do you break up and loosen the soil? How else do you kill all the weeds? How else do you build fertility?

In a no-till garden, these goals are achieved in a couple of simple ways:

1. Aerate using a broadfork. This is a fun annual spring ritual. The broadfork allows you to gently fluff up the soil and improve its structure without turning it over completely. It’s a garden chore my daughter loves doing with me — we rock back and forth, she can’t stop laughing, I get good exercise.

 

 

 

2. After broadforking, layer on a “lasagna mulch” to suppress weeds and build fertility. In other words, you layer on different types of organic material, one of which is a weed block layer like cardboard or newspaper. On garden beds, I like using a few layers of wetted newspaper because it breaks down faster.

There are many variations to lasagna or sheet mulching. Mine usually ends up looking something like this, from bottom layer to top layer:

  • bottom: slashed vegetation (any weeds or cover crops on soil surface)
  • any soil amendments
  • thin layer of composted manure
  • newspaper or cardboard
  • 2 inches of compost
  • top layer: seedless mulch, like straw, leaves, lawn clippings, or cut-down cover crops

All these layers gradually break down, and the compost or manure invites lots of juicy earthworms that aerate the beds and gradually pull the organic materials deep into the soil.

The mulch shades the soil, blocks weeds, and creates fantastic habitat for soil micro-organisms, which are your partners in building good soil.

You can literally see yesterday’s news turning into good garden soil! Now there’s something to meditate on while gardening.

Once all the beds are established in this way, you can simply plant seeds into the newly formed, weed-free bed. Or, in case of transplants, break a little opening into the wetted newspaper layer and transplant directly into that hole. You now have an effective advantage over the weeds: by the time they break through the mulch, the plants you want are already well-established.

 

My favorite video resources for No-till gardening:

How to make a No-Dig Garden with Morag Gamble

Anything by Charles Dowding, but especially this and this