Building a hugelkultur mound in a city backyard

This was a leap-of-faith project during Michigan’s bleak COVID-19 “shelter-in-place” period. I’m documenting it here as a plan for building a hugelkultur bed on a small city lot as well as to preserve a pleasant COVID-19 memory. Behold the thriving hugelkultur mound:

Hugelkultur is a permaculture concept where you pile up organic material (logs, leaves, compost, etc.) and then grow a garden on top of it. Here is a good explanation of hugelkultur and its benefits. It’s also a fun word to say. We refer to our mound as “the hugel” [German for hill].

This was the perfect COVID-19 project. Under lockdown in April, we had nowhere to go. I was spending lots of time with my kids at home during the day. And I wanted to be outside. Building a garden bed with the materials at hand was a small act of protest against the feeling of being dependent on a global supply chain whose fragility had suddenly been exposed. I couldn’t easily get soil or lumber delivered for a conventional raised bed. And crucially, the city’s compost and yard waste collection was about to resume for the spring, so my neighbors had their maximum amount of organic material awaiting disposal.

Starting with a hole

I started by digging a hole on which to construct the mound. Sort of like a basement for the hill. This allowed for building a mound that appears shorter than its full height. Conveniently, the soil removed here formed the eventual top layer of my hill. Remember to call Miss Dig to make sure you don’t hit any buried wires or gas lines.

Then it was time to build a hill on top of the hole, using as much plant matter as I could find.

Bring Out Your Dead (Plants)

Based on what I see on the web, hugelkultur seems practiced primarily on rural properties and homesteads rich in space and discarded trees. I, however, live in a city, on a tidy 6,500 sq ft lot. Around my yard I only had a few branches and odd piles of oak leaves. So the big challenge was getting all the plant matter I wanted.

I sent a message to my block’s email list and my neighbors replied they’d be delighted to give me their yard waste. Over a few days I carted home wood and yard waste from nine different neighbors. This included my two immediate neighbors on each side, two across the street, and the family behind me. It’s good to befriend the people you live with! My hill ended up including :

• Four wheelbarrows of huge chunks of rotting boxelder wood that had proven poor for bonfires
• Many yard waste bags of leaves
• Several wheelbarrows of raked up branches and twigs
• A discarded Christmas tree
• A dead rosebush
• Fresh trimmings from a magnolia tree
• Three large tied bundles of freshly trimmed yew trees. They were tied for curbside compost pickup, I left the bundles intact since they were more compact that way.
• Half-composted food matter that had accumulated in a compost cart over the winter

Plus other odds and ends. Here were the box elder chunks:

These massive chunks went on the bottom, filling up the hole.

I packed leaves and smaller matter around the big pieces, then built up the hill, alternating fresh and rotting plant matter, ending with leaves on top.

I cut up bigger pieces that were poking out (like the Christmas tree) and stomped and shoved the pile into the shape I wanted.

On top of the leaves I replaced the soil I’d dug up in the beginning. I placed it grass-side down, letting the grass become part of the hugel. This gave me a layer of topsoil about 4″ deep.

Digging a rain garden and building up a hill

More than one rural practitioner of hugelkultur has mentioned digging a pond and using that dirt to top their mounds. Applying this idea at the backyard scale, I dug a rain garden where my back gutter emptied out onto the lawn. That excavated soil went onto the hill as well, making the total soil layer on top about 8″ deep. (The rain garden has been a satisfying project on its own but that’s for another post).

At this point I had a hill about 3 feet tall. My 5 year-old enjoyed climbing it and jumping off. This probably compacted the soil on top, but he helped enough with building it to earn this privilege.

Clover as green mulch

Another tip I got from the web: I sowed the entire hill with white clover. It felt questionable at the time, but I’m glad I did. The clover serves a few purposes:

• Stabilizes the soil from runoff. My hill is fairly steep and when it was bare, water on the top would carry dirt down the hill. The clover’s roots hold the dirt in place.
• Blocks out weeds and retains water (like regular mulch).
• Fixes nitrogen in the soil. From what I read, clover can certainly fix nitrogen, but the extent to which it happens may depend on the bacteria present in the soil, which isn’t a given.

I bought a pound or two of white clover seed in bulk from Downtown Home and Garden and broadcast it on the bare hill. (I’ve also been using clover to fill bare patches in my grass). The seed needed daily watering, but in my case a rainy spring did the job.

Here’s the mound with a crude temporary border and the clover just starting to sprout. I’d just planted a few zucchini and bean seedlings.

When the hill was covered only in a blanket of green clover, my children observed that it looked uncannily like the rejuvenated Te Fiti island at the end of Moana. (not pictured, unfortunately).

The finishing touches: a border and mulch

The hugel needed a border to separate it from the grass. As it was, it looked like someone had dumped a load of dirt on the grass and I’d planted it. The answer fell into my lap when my neighbor who’d provided the large hunks of box elder told me, “I mentioned your project to my friend and he asked if you’d take his rotten firewood.”

The friend-of-a-friend brought over his trailer of rotten logs. It was all pretty far gone but many pieces had intact bark. I cut the hill back where it met the ground, piled that soil back onto the hill, and installed the rotten logs as a border/retaining wall.

Finally: planting vegetables

At last the hill was ready to plant. This part is mostly like planting a conventional raised bed. The main difference is taking the hill into account. For instance, plants on the north side will get less sun until they’re taller. And plants might be able to grow a little closer together since they have separation in three dimensions, not just two.

That’s another bonus of a sloped hugel mound: there’s more surface area to plant. The area of a circular flat raised bed would be π*r^2, while a hemisphere hugel mound in the same footprint would have double that planting area, 2π*r^2. My hill is not a perfect sphere, so it’s not a 100% increase, but there’s definitely more room.

Between the garden variety plants and adding a border of mulch around the logs, it looks less wild and more compatible with the aesthetic of a tidy urban backyard. Though I didn’t master the distribution of the plants or account for how big they’d get, and now I have zucchini, pumpkin, and tomato plants spilling out over the border.

Seeing yard waste differently

I’ve gradually begun to see the natural world differently (reading books like The Overstory and Timefulness helped). Building the hugelkultur mound further contributed to my worldview as I became more aware of how the cycle of organic matter plays out on my street.

In the wild, fallen plant material rests in place, housing creatures and feeding future plants. In the city, plants still produce leaves and dead limbs, but we interrupt the cycle, treating the plant matter as waste. Each week the compost truck comes to haul away our leaves, sticks, logs, and garden trimmings.

During this project I scrounged for all the plant matter I could get my hands on. My neighbors’ waste piles became the structure and substance of my summer vegetable harvest. In particular, my view of leaves was transformed. Our street is lined with towering oak trees. Each fall our block collectively sets out hundreds bags of raked leaves to be hauled away. Other fallen leaves cover the road and clog the storm drains.

This spring my immediate neighbor (who is also on a permaculture gardening kick) and I began coveting the leaves as mulch and as “browns” for composting. In April, at the start of my hugelkultur project, he offered to shred all the old leaves I could use from a third neighbor’s stash of leaf bags. By late May, when I returned to him looking for extra shredded leaves to use as mulch, they were gone. He’d needed all he could get.

On a small city lot, it would be difficult to manage all yard waste on-site, at least without reimagining one’s yard to minimize external inputs and outputs. And it’s great that our yard waste bags of leaves are hauled to the city compost center, not to a landfill as they might be elsewhere. My conventional raised bed in front of my house is full of this excellent municipal compost.

But to the extent possible, it feels ideal to keep the plant matter at the site where it falls, preserving a more intact cycle. My hugelkultur project achieved that, while also accomplishing the contrapositive: keeping external matter out. Compared to a traditional raised bed, there was no imported soil, no lumber or hardware, and no cost. Just my neighbors’ branches and leaves.

I’m excited to watch the hill change as the inside decays over coming years. How much will it shrink? When will the soil nutrients peak, and when will they be depleted? So far it’s an unmitigated success. The first year’s harvest is exploding.