What would you say if I told you that you could build the best garden bed you’ve ever had with waste material gathered from your own yard that requires no fertilizer or regular watering? Sounds pretty good, right? Almost too good, I know. So what is it then, you ask? The answer is hugelkultur. Many of you have probably never heard of it and that’s fine, because you’re about to learn everything you need to know. Hugelkultur is a method of growing vegetation that has been around for centuries. It developed with the Germans as a way to utilize stumps after they had cleared land for farming. It actually means “hill culture” or “hill mound” (sometimes referred to as “hill gardening” or “mound gardening”). It’s a practical, effective, and resilient technique to utilize biomass “waste” that collects naturally in your yard or property and would normally be disposed. No organic plant matter in your yard needs to be seen as “waste” and destined for burning or putting in yard bags to be hauled off for disposal. Essentially any yard byproducts normally discarded of, including sticks, limbs, rotting wood, leaves, grass clippings, dead plant material, and compost can be incorporated into a huglkultur mound. The genius of hugelkultur is of course not borne of our own ingenuity. We are merely replicating a natural process that already happens once a tree falls and gets mounded over with organic material, which creates a rich forest floor where nutrients get cycled back in and vegetative/fungal growth thrives.
Benefits Of A Hugelkultur Mound
The benefits of a hugelkultur mound are many and have proven to be effective for centuries. They include:
- Moisture retention – the woody detritus soaks up large amounts of rainwater and slowly releases it, which is particularly useful during times of decreased precipitation and drought
- Resilient use of “waste” biomass material for a closed loop system
- Long term fertility building that greatly reduces or eliminates the need for fertilizers or additives, which degrade our precious soil resources
- No till gardening solution
- Very low maintenance
- Easy to build and customizable in shape and size to accommodate any space or objective
The Backbone Of The Mound
Now, let’s get started with the basic. Hugelkultur starts with wood – decomposing wood, more specifically. This is an important distinction to make and to remember as green (or recently living wood) will actually rob nitrogen from the soil, which can severely impact the growth and health of the plants you are trying to grow. The idea with hugelkultur mounds is you want to create a rich, airy, water-retentive growing medium from organic matter that decomposes over time. The biggest driver of this nutrient-rich composition is the wood. Whether it be decomposing logs, branches, stumps, wood is both the structure and the fuel of hugelkultur. Decomposing wood essentially acts as a sponge that absorbs moisture and releases it slowly, which helps to give consistent water supply to plants even during droughts. As wood decomposes, it forms air pockets which provide oxygen to roots and prevent compaction. Perhaps most importantly, however, the decomposing wood leaches nutrients that will be taken up by your plants for possibly decades. On top of all of these phenomenal attributes, hugelkultur is also a no till option. Many of us have been told or shown that in order to establish a garden you need to till up the existing soil, plant your seeds, and go about the growing and harvesting process. This is actually accepted as a poor practice. The subterranean environment under our yards is composed of an interconnected and complex web of microbes and other organisms that break down and recycle nutrients to keep soil productive. When we till up our land, we are disrupting these communities and actually compromising the health of the soil. A better option is to keep the underground dynamics in place and instead enrich it by laying organic matter on top.
Non-Woody Components Of The Mound
Now that we have seen that wood is the backbone of a hugelkultur mound, let’s look at the other non-woody debris that goes into them. Besides logs, stumps, and branches, you can and should use an assortment of other organic components to add bulk to the mound and round out its nutrient-profile. These can be things such as: grass clippings, plant trimmings, leaves (preferably chipped) from both deciduous and evergreen trees (needles), straw, compost, topsoil, and other non-treated organic material from your yard. These can all be layered to make a highly nourishing structure for plant growth and prosperity. With that being said, there are a few notable exceptions that you should be aware of and they are known as allelopathic plants. Plants within this classification produce chemicals that can inhibit or promote growth of other plants. Black walnut trees in particular are well known for this and can produce troubles for your mound. Stay away from known allelopathic plants. Educate yourself on allelopathic plants here (include link).
How To Build A Hugelkultur Mound
The structure of a hugelkultur mound is such that the larger dead logs, stumps, and limbs should form the base. This base will take longer to break down and will act as the foundation “sponge” for the structure and should be thought of as a nutrient provider in the long term as it will not provide nutrients for plants right away. The base can either be dug into the ground or sit flat on top of it. For those that are building a hugelkultur mound on grassy lawn, you can dig out the sod that encompasses the footprint of the mound. Then, you put the base logs and stumps into the shallow trench that is formed and then use the sod (turned upside down) as a component of the mound itself, for a maximum closed loop structure. For those that are working on a slope or uneven surface, digging the base of the hugelkultur mound into the earth can allow for an even footing and stability. One additional thought to the buried hugelkultur mound, of which I have not confirmed myself or from others, is that a fully or partially buried base of wood may speed up the breakdown and decomposition process as submerged wood will most likely be exposed to more microbes and moisture. If you are working on ground that is relatively flat, having the base of the mound on top of the ground is perfectly fine. On top of the base, there should be smaller branches and sticks. On top of that you can put your chipped dead leaves and grass clippings. These leaves and grass clippings decompose faster and will therefore provide nutrients for the plant roots that penetrate several inches down. After that, put a layer of compost a few inches thick. Finally, to top off the mound, apply 1-2 inches of topsoil.
What To Grow In A Hugelkultur Mound
Let’s recognize that a hugelkultur mound is much like any other garden bed in that it is preferable to let it sit for awhile before you start to plant in it. By letting it sit for a few months or even a year, you’re allowing the components to settle while also allowing some decomposition to occur. This will add strength to the structure, release nutrients, and give time for microorganisms to colonize and get to work. Do not worry if you want to get started now, as long as you have used decomposing wood to construct the mound then you should be able to start shortly after completion. The minimum time I would say to wait to start planting in the mound is a week after it is completed. It is commonly stated that shallow rooted and vining plants such as squashes, melons, and pumpkins do best. I personally have had great success with these. Hugelkultur mounds heat up faster and therefore you should recognize that mounds located in full sun will get considerably warmer, which is great for heat-lovers but your cool weather crops will probably get stressed. And until your hugelkultur mound has started to break down after a season or two, you will probably not have too much success with tuberous or bulb vegetables since they may not have enough room to fully develop.
Observations Of A Hugelkultur Mound
I built my hugelkultur mound a couple of months ago in early spring. I made mine with a mixture of partially decomposed soft and hardwood logs, topped with (in order from bottom to top) leaves, woodchips, leaves, and topsoil, which were all things that I had at my disposal on the property. I would have added compost just under the layer of topsoil, but alas I did not have any. It has maintained its structure and stability well and none of the components that form it have been displaced by course of run off or collapse. I don’t think this has anything to do with my skills constructing it, but rather everything working together by being woven and shaped into the desired structure like a bird’s nest. I decided to really put my hugelkultur mound to the test and only put about 1.5-2 inches of soil on top, just enough to bury my seeds and rely on everything else to work as it should.
One of the first things I noticed that the soil was drying out really quickly, granted I happened to finish the hugelkultur mound in the midst of an unseasonably warm and dry spring with temperatures up to 30 degrees above normal and the first several days were part of a two week stretch without any rain. At the beginning, I found myself having to water the hugelkultur mound frequently at both morning and night to keep it from becoming bone dry on top because of full day sun exposure, hot temperatures, and wind. I added a layer of straw to the top of the mound and wood chips to cover up the sides so that it may better retain moisture, which it appeared to do well after that.
A shortcoming of the mound for a beginner is that you do not know what is going on inside the mound because it is inaccessible to view. Since you do not want to disturb the mound with seeds and/or seedlings planted in it, you do not know if the inside is moist, decomposing, etc. So although the top layer of soil was drying out, that’s not to say the inside was dry too. I found myself not knowing whether I was watering it the right amount or overwatering. I was worried to cease watering for purposes of experimenting to see if it would impact the plants because I did not want to lose them during the heat. I have since backed off after adding the straw and wood chips and only water the mound sparingly and it has appeared to thrive.
An unanticipated observation is that the mound attracts birds, which I’m sure is due to the vantage point, warmth, and plethora of bugs that collect on it. None of the seedlings appear to be impacted and there doesn’t appear to be any disturbance to the soil, just bird droppings as a memento. I planted my pumpkin, watermelon, squash, zucchini, beans, corn, and cucumber seeds into the mound. They all germinated quickly and have thrived in the thin layer of topsoil with only the organic matter beneath.
I have had tremendous issues with slugs on the mound. They are all over the yard to begin with, but seem particularly attracted to the mound, probably because of its moisture and internal spaces that they can hide in during the day. I have had to kill hundreds of slugs that gather on it. If I could back, I would have put a layer of fine wood chips further around the mound to allow a larger buffer to stem their advance. I would have covered up the sides of the mound with wood chips quicker as well which would have prevented them from colonizing the interior spaces from the onset.
The last thing I would have done differently would have been to check for gaps in the organic material that it is comprised. I have discovered some soft spots where there is topsoil on only a thin layer of organic material and a large space between that and the organic material farther down in the mound. This may pose issues if roots start penetrating down further and hit these gaps where they are unable to reach nutrients. If I could go back, I would have broken up the sticks more so that they didn’t prop up certain areas and cause the spaces inside.