“No-Dig”/”No-Till”: Adding 6″ of Cured Compost

Gardeners have been planting in compost heaped on top of the soil for at least as long as people have recorded such things. French Intensive gardeners were planting in 18 inches of cured horse manure placed on top of the existing soil going at least as far back as the 1700s and 1800s and likely back to the 1500s, and this tradition continues among gardeners to this day. Ever since I was a kid, I’ve observed gardeners of all kinds use this method as their best solution for a multitude of unique situations, including my father for everything from greenhouse beds to raised planting beds growing everything from grapes to plumbs, to ornamental flowers, to vegetables. However, giving credit where it’s due, most of the recent uptick in this method can be traced to Charles Dowding and his books Organic Gardening: The Natural No-dig Way and How to Create a New Vegetable Garden.

Pros and Cons

Pros

This “no-dig” or “no-till” approach has several benefits: It keeps the soil’s structure intact, only minimally destroys or disturbs soil life, and buries weed seeds where they’re less likely to sprout into a new crop of weeds. Furthermore, it adds crucial organic matter to the soil, as all good methods do, and allows gardeners a place to start growing a garden while they’re smothering the vegetation underneath it. Plus, most plants grow quite well using it.

Cons

There are, however, some possible cons to this method, the first three of which only apply if one smothers the preexisting vegetation with newspaper while building the bed, which is just one of the techniques described below. Still, each of the cons of this particular technique deserves a brief explanation, if only just to allow you to make an informed choice when deciding which vegetation-clearing technique to use.

Too Little Rooting Space

First, since the newspapers take a few months or so to break down enough to be easily penetrated by roots, the six inches of compost added on top of the newspapers is not enough to accommodate the fullness of most garden plants’ massive root systems. For more on this, see “Pros and Cons of “No-Dig” / “No-Till” Methods.”

Dries Out Quickly

Second, cured compost sitting above the surrounding soil dries out quickly anyway, but it dries out even faster if it’s isolated from the soil below by a thick layer of newspapers that block the moisture-replenishing wicking of capillary action from the deeper water table below.

Compacts Underlying Soil

Third, in our tests, layers of newspaper under the compost seem to act like a big snowshoe to combine the weight of the compost, compacting the soil underneath it.

Doesn’t Aerate Deeper Soil

Finally, while it provides one of the key ingredients to soil and plant health (organic matter) it does little to provide for the other (aeration) and even works against it a bit. While the added organic matter will be plenty aerated since it was loosened naturally as it was added, placing compost directly on top of the existing soil does nothing to aerate the deeper soil. If anything, it decreases the amount of air getting to the deeper layers of soil. Since available organic matter to eat and the soil aeration to provide needed oxygen and other elements is key to microbial growth in the soil, and microbial growth in the soil is the key to ultimate soil and plant health, this is a key detriment of the classic “no-dig”/”no-till” method.

How To Fix These Cons

Luckily, other vegetation-clearing techniques almost completely eliminate these issues, and some even enhance root space, water retention and wicking, and soil looseness and friability.

If gardeners aren’t dogmatic in their “no-dig”/”no-till” approach and loosen the soil—with a digging fork, spade, broadfork, or even a method like double-digging—the first year, they get all of the benefits of aerating their soil deeply while maintaining the ease of the “no-dig”/”no-till” approach.

Still, there is one possible detriment to this method no matter what vegetation-clearing technique one uses, or perhaps it’s just a possible ethical question: Is using such a large amount of cured compost sustainable? For more thoughts on that and on all of these benefits and possible detriments see my post on “Pros and Cons of “No-Dig” / “No-Till” Methods.”

The Method

The method itself is incredibly simple. The most complicated part is your first choice. After that, it’s annoyingly simple.

Step 1 – Clear Existing Vegetation

Your first step is to decide how you want to clear the area you intend as a bed of its existing vegetation, so it doesn’t grow up through your “no-dig”/”no-till” bed and become a weed problem. While smothering when building the bed has the most cons, each of the five options has its own advantages and disadvantages depending on the persistence of your existing vegetation and the tools and time you have available. For example, smothering in advance is easy, takes zero tools, kills persistent weeds and sod, and is by far the best option for soil and plant health, but it requires you to take action up to a year in advance. Similarly, while smothering when building the bed creates three specific conditions antithetical to ideal garden plant health and production—dry, shallow, and compacted soil—it also lets you start gardening in the bed right away, even while the vegetation is being smothered.

In short, there is no one right way. I present them here as options, so you can pick the method that works best for your unique situation. Plus, the point is that you bring the joy of gardening into your life (or expand upon it), not that you’re perfect or have the perfect method. The seeds, soil, and plants do the real work anyway, and, together, they already know how to grow. Our job is to observe and be open to learning better ways to best foster their growth over time. So feel free to experiment with several options and compare the results. It’s wildly entertaining.

The Five Options

Option 1: Smother in Advance.
Advantages: Best for soil health
Disadvantages: Need lots of lead time

Option 2: Smother When Building the Bed
Advantages: Can smother persistent weeds and sod and grow garden plants right away
Disadvantages: Leads to drier, shallow planting bed and compacts soil underneath

Option 3: Mow and Till
Advantages: Works in sod and persistent weeds and sod immediately, so you can plant right away and eliminates all cons of option 2 (e.g. provides additional loose soil for plants’ roots)
Disadvantages: Need a tiller and not purely “no-till” or “no-dig”

Option 4: Dig the Weed and Remove the Sod
Advantages: Removes weeds and sod immediately while eliminating all the cons of option 2
Disadvantages: A lot of work and takes some important organic matter out of the bed to the compost bin

Option 5: Just Mowing
Advantages: Easy and eliminates cons of option 2
Disadvantages: Can only be done if you have relatively “well-behaved” weeds or sod

Step-by-step instructions for each of these options can be found in my post on “Clearing Existing Vegetation For “No-Dig”/”No-Till” Beds.”

Clearing Existing Vegetation for “No-Dig” / “No-Till” Beds

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Step 2- Loosen the Soil (Optional)

If you’ve smothered the weeds and sod in advance, tilled in or removed them, or just mowed them, you have one other option that fosters even healthier and more productive plants: loosening the bed’s existing soil as deeply as easily feasible before moving to the next step. Forking or spading to the depth of a foot, or even tilling six inches deep, now will vastly increase the ease of plants rooting deeply, especially in previously compacted or inherently hard soil like clay. While technically not strictly “no-dig,” or “no-till” this option can be thought of as a wonderful hybrid alternative that will provide wonderful benefits for the health of your plants for years to come, especially since, in future years, you won’t be able to do this again without disturbing your “no-dig,” or “no-till” bed.

It is often claimed that, when you use this method, the soil below will loosen significantly after the first year or two as worms integrate the compost into the deeper layers of soil. Interestingly, we’ve tested this claim and haven’t found it to be the case. Earthworms just don’t work like that. While we see earthworm borrows integrating compost deeper along their edges during our unearthing inspections, it’s not like the soil and compost are all mixed together into some loose, friable, well-integrated soil. In fact, the soil in general is more compact than it was the day we added the compost, under newspapers significantly so. With this in mind, taking a little extra time not to loosen it now really helps the long-term health of the bed.

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Step 3- Add Compost

The final step is easy. Just add six inches of cured compost to the entire area of the bed and you’re ready to plant. It’s that easy, but I’ve added some help for some of the finer points below.

The Nuances

Figuring How Much Cured Compost to Buy

To figure out how much cured compost you need, first, measure the lengths and widths of all of your beds in feet. Then, multiply each bed’s length by its width to find its area. Divide each result by two (since the added compost is half a foot deep) to get the volume in cubic feet for each bed. Finally, add the volumes for all of the beds together to get your total volume needed. Bags of cured compost are typically sold by the cubic foot (i.e. one bag = one cubic foot), so your total volume in cubic feet is also how many bags you need. If you buy your cured compost in bulk, however, it is sold by the cubic yard. Since there are 27 cubic feet in a cubic yard, just divide your result from above by 27 to figure how many cubic yards you need.

Where to Get Your Compost

If you need a large amount, bulk cured compost is almost always a much cheaper option. It might even be cheaper to get more than you need and use it somewhere else or save it for next year. If you don’t or can’t buy it in bulk, bags of compost are available at most nurseries, garden centers, farm supply stores, and big-box stores. Oftentimes, if you ask at your local nursery or farm supply store, they’ll give you a discount per bag if you’re purchasing a large number of bags. It doesn’t hurt to ask. For more tips on procuring enough compost at a good price, check out the “Where to Get It” section of my post on “Adding Cured Compost” in the “Building Soil” “chapter” of my website.

Adding a Barrier, Even Temporarily (Optional But Really Helpful)

It helps to have some sort of containing border in place, even a temporary one, before adding the compost so it doesn’t spill everywhere as you fill the bed. After a week or two, the compost will settle and become more stable, especially if you have some gentle rains, and you can remove the border if you don’t like it.

You can use just about anything to make a containing border as long as it’s at least six inches tall. You can use cinder blocks or boards held in place by stakes or screwed together at the corners, or any combination therein. Or you can just use mulch. One of my favorite methods is to lay wetted newspapers or cardboard under the path areas and add fluffy leaves, straw, or marsh hay as a path mulch just before I add the cured compost. Before they’re compacted by walking, they’re easy enough to keep fluffed to six inches or so tall, providing a perfect barrier to the splashing and spilling that otherwise takes place when adding the compost and completing a task that would typically be the next step in the process.

As the leaves, straw, or marsh hay mats down and decomposes over that first season, wood chips over cardboard offer a more durable replacement. Another easy option once beds are established is to lap the newspapers (or cardboard) up a bit onto each adjacent bed (as shown in the pictures above) before adding the mulch, just to provide another barrier to “compost migration” into the path. You can also add the compost without a border of any kind and just rake it back into the bed when you’re done.

Adding Grade Stakes (Optional)

I also like to put in some grade stakes in the bed just to make sure I’m adding a full six inches and keeping it evenly distributed. To easily do the same, mark a line with a marker six inches down from the top of the stakes, and pound them in to that line, leaving six inches of stake above the ground. Once the stakes are barely covered, you know you’re at the correct depth of compost. Having the stakes below the level of the top of the compost also makes moving the compost around easier, since you’re not having to maneuver your rake around protruding stakes.

Future Years

Each year thereafter, after clearing garden debris, just add a two-inch layer of cured compost to the entire bed and you’re ready to plant again.