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Anatomy of a No-Dig Raised Bed

Veggie dog Dave on his evening rounds, contemplating what worked and didn't, this spring-summer season.

According to multiple sources, close to 20 million North Americans took up gardening in 2020, and a huge percentage of those who grew food, hope to continue.

Empirical and anecdotal data however, reveals that many new gardeners encountered frustrations and difficulties along the learning curve; frustrations that may encourage them to quit. This doesn’t surprise me at all, because while gardening is a simple and natural process, many of us have strayed rather far from nature. Nature herself has strayed off balance, sending extreme weather events like heatwaves, droughts and flooding, to remind us that we all have some course correction to do.

The good news is that urban permaculture ethics and principles offer dozens of natural-system-based failsafes that can build resilience into our food gardens and create a strong foundation for achieving regional food security. The practice of 'no-dig', or 'no-till' gardening is chief among them.

It was such a challenging gardening season, even Dave considered throwing in the towel.

I will happily share what I’ve learned by failing, so that readers don’t have to. My hope is that enthusiasts stick with food gardening and reap its delicious, healthful, climate-positive rewards.

My own experiences speaking with and teaching people about food gardening this past two years have centred around the idea of raised beds, specifically ‘no-dig’ raised beds. I receive many emails on the subject, inquiring about materials and methodology, so I thought it might be time to create a brief 101 for consideration.

Like most people, I am motivated by simplicity, economy, and sustainability. For that reason, I recommend using inexpensive untreated or organically treated cedar to build open-bottom raised beds, and consider planters made of steel, stone, or untreated wood. Plastic will do of course for large planters, but the soil will dry out more quickly in plastic, and some plastics leach unwanted contaminants into food garden soil. I won’t buy new plastic pots, but in a pinch I use the ones that I have. Also, I pass them along to other gardeners who would otherwise buy new.

Fall delivery of a great steaming tiptruck load of organic compost is cause for great celebration.

While it may seem counterintuitive, later summer and fall are the perfect times to prepare for next gardening season. Creating new no-dig beds now, to rest quietly but industriously over the winter, makes sense.

If you observe nature during these next few months, through to first frost, you will see that she is in fact very busy getting a jump on spring. We can emulate this natural logic by assembling or top-dressing layers of biologically diverse organic material before winter takes root, to allow the still-warm weather to kick-start fungi, microbes and other microorganisms into creating luscious soil.

Rain and melting snow will wash high concentrates of salts from contained animal manures, and distribute microscopic elements, helping to balance and fortify living soil for spring planting. Cover crops like winter field peas provide masses of organic mulch matter, fix nitrogen, and look beautiful. Mulched brown leaves provide excellent winter cover, and while they break slowly down into the soil, create habitat for beneficial insects and other organisms.

Our daughter Gabrielle is a master raised bed builder. No experience required though to assemble these beds.

No-dig garden beds (raised or in-ground) and containers are fundamental to urban permaculture. Whether you live in a suburban neighborhood and tend a backyard garden, or nurture soil-filled grow bags on a sunny ledge or rooftop, your efforts will be more productive, beautiful and righteous if you adopt a no-dig philosophy.

Why? Because at its roots, no-dig mimics nature's logic, and in following her you simply cannot go wrong (or at least, not often). In natural ecosystems undisturbed by human intervention, nature top-dresses the soil from above and from the forest canopy, while simultaneously and invisibly conducting a symphony of beneficial relationships below ground. Happy 'contained' soil looks very much like moist chocolate cake, offering a deep brown-black damp, sticky sponginess much like a black forest chocolate cupcake.

Upturned sod surrounds in-situ worm compost set level with the top edge of the bed rails.

This is no accident. Healthy soil is busy soil, supporting an ecosystem of visible and microscopic organisms whose job it is to decompose plant residue and carry out a range of important functions. The less disturbed (tilled, dug) the soil and the greater the amount of beneficial organic matter retained, the more plant residue and food there is to support biological activity.

Worms feed on decomposing plant matter, and as they move through and poop in the soil they aerate and fertilize at the same time — contributing to the sponge and structure. In circulating, feeding and pooping, worms and larger insects are captive, living recyclers of soil.

Tiny microfauna like protozoa and nematodes, and microflora like fungi and bacteria are equally important to soil biology and play specific roles within the biomass of the soil. Healthy, living, diversely planted soil is our best defence against moisture loss and erosion.

Drill quarter-inch holes along the sides and bottom of the bucket, to within four inches of the top.

I do not dig, turn over, or otherwise unnecessarily disturb the soil, and I never use synthetic fertilizers or insecticides that would harm organisms and kill or harm soil biology. We harvest plants at soil level by cutting the stems and leaving the root structure to decompose naturally and become food for organisms. There are exceptions of course, but very few.

Disturbing the soil can damage or destroy the airy network of tunnels that worms and insects worked so hard to create, and it breaks the mycelial network of fungal hyphae (mushrooms are the fruiting bodies of this underground network) that can traverse hundreds of thousands of miles back and forth through the soil contained in a single small bed. This network creates mutually beneficial relationships with plant roots and root hairs, exchanging nutrients and minerals, and increasing the nutrient and moisture absorbing surface area and capabilities of the roots.

Two layers of brown cardboard ensure that weed and grass seeds won't ever germinate and grow up into the beds.

When nature composts from the top with leaf litter and decaying matter, organisms in the soil come to the surface to feed and pull the matter down below the soil — aerating and adding structure in the process — and the decomposition process is enhanced.

Rustic and inexpensive cedar beds can be dressed up with the addition of pea gravel and garden statuary.
A thrift-store vintage iron firescreen trellises cucamelons and groundcherries, adding elegance to humble beds.

In addition to the nine large raised cedar planters we have in our front yard urban permaculture garden, we have smallish planter pots and farm animal feed-trough planters that have supported very healthy tomato plants, fruit trees, and root vegetables for well over a decade. I have never replaced the soil or turned it over by digging, but I do top-dress generously every year with organic compost.

The soil levels naturally drop as organisms and plants feed on the soil, breaking it down and turning it into food for my family. It is miraculous really, what goes on down below and over time, and how intelligent the soil web of life really is.

No-dig patio planter of tomatoes, kohlrabi, eggplant, peppers, basil, and beets. As beautiful as it is productive.

In creating a no-dig raised bed it is helpful to consider the information provided above; think like an edible ecosystem, then begin. Here is what you will need:

Elements of a No-Dig Raised Bed

  • For on-surface beds. Level or near-level ground that is not contaminated by chemicals, oils, or poisons of any kind. Building raised beds over pavement or other impermeable surfaces is an option (for another day) but it inhibits the movement of soil biology, organisms and microorganisms from the beds to the earth below, and back again.

  • Brown cardboard, enough to cover the area beneath the bed, allowing overlaps of 3-6 inches to prevent grass and other plants growing through.

  • Enough organic or natural soil as you need to fill the bed. To calculate this volume, multiply the length of the bed, by its width, then again by its depth. For example an 8’L x 4’W x 2’H bed requires 64 cubic feet of soil, which equals almost 2.5 cubic yards (there are 27 cubic feet in one cubic yard of soil).

  • If using — enough organic compost to replace the top six inches of soil. To calculate this number, divide the square footage of the bed by two. An 8’L x 4’W bed covers 32 square feet, and would then require 16 cubic feet of compost. You would then deduct 16 from 64 (your bed volume), and order just 48 cubic feet (1.75 cubic yards) of soil.

  • Cedar for the sides and ends of the bed. I used 8’ lengths of 1”W x 8”H cedar for the sides, and 4’ lengths of the same cedar for the ends. I stacked the wood two-high, making my beds approximately 16” high. Each bed then required four each pieces of 1”x8” rough cedar cut to 8’ and 4' lengths.

  • Corner hardware of choice — “L” brackets, hinges, etc. I used stackable corner hinges from Lee Valley. They are galvanized, easy to use, and relatively inexpensive.

  • Heavy duty, tightly woven cotton fabric or denim to line the side of the assembled beds to within three inches of the top — dark colours are best. This is only necessary to keep soil from spilling through the seams between rows of wood, and is unnecessary if beds are only one row high.

  • Staple gun to affix the fabric, if using.

  • Wooden garden stakes to affix inside the beds, mid-way along the long sides of the bed, to keep wood for bowing under pressure of the soil. These are not necessary if you are using 2” thick lengths of cedar or other wood.

  • Stainless steel or galvanized screws for stakes, if using.

  • Organic wood preservative, or no wood preservative.

Kitchen organics mix with garden trimmings, red wriggler compost worms, and tiny jet black worm castings (poop).

Depending on where you live, other naturally rot-resistant woods may be available. I do not recommend using woods that are not rot resistant simply because it is both difficult and ill-advised to empty beds of soil to replace wood after just a few years —- we are aiming for no-dig, no-disturb.

Interestingly, it is possible to replace side rails carefully, one at a time after several years, once the no-dig ethos has created substantial soil structure and mycelial network. We did this recently with a 20 year-old part-sun bed in which the soil held together like a giant black sponge while we slowly and carefully replaced its 2”W x 10”H x 6'L sides.

I do not recommend using plastic or petroleum-based fabric or planks for beds, or for wrapping wood to prevent rot. Wrapping both repels and retains water, which could hasten in fact decomposition, plus keeping plastic out of our food gardens whenever possible is a good idea.

The list above assumes that you are starting from scratch, placing a raised bed over grass or bare soil, and that you wish to fill your bed with just soil and compost.

Settled and ready for planting, new food garden beds all in a row.

I filled the bottom six inches of my raised beds with composted sod that I had dug up the previous year and left to stew in a great pile over the winter. I laid the cardboard over the sod, then filled the balance of the beds, right to the top, with organic composted soil (organic green compost, sand, wood fines, four types of manure). After a few weeks, the soil level had settled by about three inches, which was perfect for sheltering small seedlings from wind. Also, I sprinkled hardwood ash over the sod before adding soil, making potassium available as needed for plants and organisms.

I inserted a DIY worm compost in the centre of each bed as well, made from recycled food grade buckets with lids. In a perfect world these buckets would be made from wood. 1/4” holes drilled through the sides (to within four inches of the top) and bottom allow for the passage of worms, food and worm poop into and out of the compost, and the lid ensures that composting odours do not attract pests. I feed my vermicomposts organic green kitchen scraps, plus trimmings from tidying the beds as I go along. It’s a great system.

In-bed worm composts create the world's best, all-natural, no-cost food garden fertilizer

No-dig applies to in-ground beds, and pots and containers equally, though there is less opportunity to layer in organics like sod. Two other beautiful and highly-productive no-dig permaculture garden installations are hugelkutur beds and keyhole gardens. I will write about those soon.

In the interim, why not show your garden a little love by creating a new no-dig bed, or convert existing beds to no-dig? Your garden and your body will love you back in spades — no pun intended.

Until next week, happy gardening!

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I use a calculator to help me track how much dirt I need. This one works really well for raised garden beds:

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