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Hügelkultur is a german word that translates to "hill culture" which is about right - cultivating on a hill of sorts. It's a practice as old as the hills, actually, and is an excellent option for storing and recycling carbon. A very permaculture thing to do if you, like us, had trees fall and were left with heaps of logs and limbs! If you don't have loads of logs and things lying around, trying to make one just for the sake of making one would be mental. Anyway...
The real beauty of a Hügelkultur is the incredibly biodiverse soil it creates. As the wood begins decomposing beneath the soil a plethora of decay loving organisms arrive to the buffet. The first responders are bacteria and fungi, then the rest of the soil food web follows. The fungi is the real star here, as it is the queen of lignin decomposition, and is an excellent companion for many of the perennial plants permaculture folks adore. The soft spongey wood then absorbs and retains water, further amplifying the presence of microbiology which both directly benefit anything you choose to plant on the mound.
There are many ways to construct a Hügelkultur, which you can find scattered about the internet. It's an art more than a science, one that people have been doing for thousands of years out of their own imaginations and not much else.
The how and why of our decision to Hügelkultur
We had the remains of numerous pines lying around in our backyard being engulfed by the same English Ivy that took its life prematurely in the first place. As we began wanting to clear it out we decided to try to capture and reuse the energy in the wood instead of spending hours upon hours at the fire pit, watching it burn off into nothing of value to us. Instead, seeing as we're gardener-farmers, we wanted to put it back into the soil. Ah, carbon sequestration! Yes, kind of, though it would have been more valuable for the tree to stay standing but alas it did not.
Before I get into the how of our Hügelkultur it's important to understand that this is just how we did it and is by no means the only way, the right way, the premium way, or what have you. It, like everything else in life, is just a way.
We had a lot, and I mean a lot of wood to deal with, but we did not have any extra soil or compost at our disposal - at least not as much as we would need to make a proper mound. So we dug, and dug, and dug some more until we had about a 2' deep, 3' wide ditch, or grave, or whatever you want to think of it is (yes we had a lie down in it, was kind of cool in a creepy way). We've done these numerous times - sometimes the ditch is 8' long, sometimes it's 40'. Like I said, we had a lot of carbon to bury. Digging down meant we would create space for the material while giving ourselves ample amount of soil to cover it all over. You need at least 6" (ideally more) to plant into when all is said and done. The amount of time and energy this takes depends on soil type, weather, and how many insanely massive stone/boulders are randomly scattered throughout for seemingly no logical reason whatsoever.
Oh and I hope that it goes without saying, but know where you're digging and absolutely avoid areas where utility lines could be. Better yet, give Miss Utility/811 a ring beforehand.
We dug it all with hand tools, just the two of us, but found a pretty efficient method that went like this: Once we had about a 3' area dug out to work in, one of us would use a heavy spade and slice the soil into chunks while the other person scooped it out with a garden shovel, setting it all to the side of the hole.
The Chunky Layer
The bottom of the bed gets lined, in a single layer, with the thick stuff; ideally quartered so that some of the flesh of the wood is exposed which helps summon the fungi more quickly than if it were still protected by its bark armor. The wood should be of varying age, decomposition states, and types. In our case we had pine and cherry - mostly pine, which was great for us seeing as we wanted to plant Blueberries which need an acidic soil. There are lists 'out there' that describe the best types of wood for this and the worst - pine and cherry are in the "OKAY" category. So OKAY we went with it, because who are these list makers any ol' way?
With the bottom fully covered in logs we shoveled a layer of soil back over it, using just enough to fill the empty spaces and cover the it all by a few inches.
The Twiggy Layer
The next layer contains smaller pieces of wood, like limbs, twigs, small chunks, bark, etc. We also threw in things like old bamboo and last season's sunflower and corn stalks. Because these pieces are smaller and will break down more quickly we piled it up into more than just a single layer.
At this point you can add any kind of organic matter you have access to - straw, hay, grass cuttings (aged), brown leaf litter, compost, aged manure, etc. Unfortunately we didn't have any of that to spare, but would have done if we did. Including any number of these things would likely, I believe, initiate the decomposition process much faster while supplying anything you plant in the hugelkulture with tons of valuable nutrients and microbiology.
Finally, scoop all of the soil that remains back onto this final layer. Be sure that every stick and twig is covered thoroughly and nothing is left exposed. If you have an odd shaped limb or two that just won't lie beneath the soil either chop them into smaller pieces or remove them. You need at least 6", ideally more, of soil across this layer so you can plant into it without issue.
It's a mound!
This is the most exciting part, where it all comes together - your limbs (the ones attached to your body) are weak but your mound culture is mounded. Depending on the type of soil you have your mound may or many not hold together for long without being mulched and/or planted. If you're working with a sandy/silty soil you'll want to cover it as quickly as possible. If plants and mulch are not an option, a tarp for a temporary solution can work. You just want to avoid it all washing away in a downpour. Using a cover crop is an excellent option if you don't intend to plant anything else in it for awhile.
Because we had so much carbon at our leisure, we chipped a great deal of it before building the Hügelkulturs which allowed us to cover the soil over, keeping it in place and readying it for the arrival of our new Blueberry and Raspberry plants.
Pro might be a stretch, but I'm savvy enough to know a few things that I think are worth sharing:
- As carbon breaks down it needs all the nitrogen it can get to proceed through the decomposition process. Therefore if you don't include something nitrogen-dense, like manure for instance, you'll have to make sure you supply it to your plants directly or the Hügelkultur will seem like a failure. For this reason we added a locally made small-batch chicken manure/feather based compost at planting and will foliar feed with compost teas and fish/seaweed fertilizer throughout the growing season.
- When you read about the history and successful practices of Hügelkultur gardening it almost always includes the mention of Comfrey. Comfrey is a great nutrient-accumulating, nitrogen-rich addition to the garden, but as a "chop and drop" it really shines in this system that is so carbon rich. Bees love it, compost bins love it, soil loves it, livestock love it, and it's medicinal! What's not to love? Well, you'd better love it because depending on the variety it can spread pretty aggressively.
- Hügelkultur has become a favorite technique among Permaculturists, for obvious reasons. It can work really well alongside a swale if you need to capture and store water (it's 2023 so who doesn't, really?). Ideally it would be positioned on the contour of your land if you intended to swale it.
- According to Michael McConkey of Edible Landscaping, the edible plant guru of this side of the country, fruit trees absolutely love carbon rich soil. So after hearing him speak in person, and knowing we intended to build some Hügelkultur beds, we dedicated a large majority of our beds to raspberries and blueberries.
- If you read much about Hügelkultur online you're going to see that they're superb at holding water. This is true, but very dependent on the type of soil you have, how much organic matter you add, and how long it takes the wood to start decomposing. Do not expect the magic of Hügelkultur to take place the first season. You'll need to nurture it and the plants while it gets going - especially in the first year.