Using Hugelkultur for Flourishing Gardens and Effective Water Conservation

By Sam Coffman

Photo by Kristina Paukshtite

Hugelkultur is a concept that has probably been around for at least centuries if not millennia. The word “hugel” means “hill” in German, and “kultur” means, well… culture. The idea is pretty simple. Stack a lot of rotten logs and other natural plant debris into a mound and cover it with dirt. This is a little oversimplified however, and I would like to explain how to use and modify this concept to produce excellent garden yields with a fraction of the water used in a flat-bed style garden watered from above.

My primary reason for first using hugelkultur in my own gardening was primarily to be able to conserve water in the very hot and dry drought years in central Texas. I found it to be almost as effective as a closed wicking bed in water conservation and an amazing way to create nutrient-dense soils that can last for years without needing much extra work once they are made.

While water conservation may not be an issue depending on where you live, hugelkultur can still be a way to get better long-term high yields from your garden for several years without as much work as raised beds and other closed systems. This is because of the way in which nutrient cycling takes place in a well-built hugelkultur bed.

In regard to where you live and whether hugelkultur will work for you, there are a few considerations. First, a hugelkultur bed works best the first season you plant in it if you prepare it at least a few months ahead of time. This is because it takes a little time for the bed to both settle and “cure” as well as the nutrient cycling to be underway by the time you plant.

Another consideration is wind. If you live in an area that has a lot of wind during your growing season, you may want to build a wind block to prevent erosion of your hugelkultur garden topsoil. The same erosion issue is true of heavy rains if they happen before your crops have grown enough to give you a root system.

Speaking of roots, the first year or two of a hugelkultur bed works better for above-ground harvests than root crops. This is because of the branches and plant debris deeper under the topsoil, such as tubers and roots, will get stuck in. This will make it harder to harvest without tearing up portions of the bed.

So aside from the excellent water conservation and nutrient cycling that one can get from a hugelkultur bed, what are some other advantages? One is that it is easier to weed and harvest from a hilly garden bed, and if it is built correctly and one does not have to worry about walking on it – especially if one is trying to maintain a no-till garden. Another is that from year to year, if you build it correctly, you can continue to plant without having to worry as much about feeding the soil from the top. Finally, you can not only get a better effect from top-down drip irrigation, but you can also automate an underground watering system if you want to set up your hugelkultur bed similar to a wicking bed.

To make a hugelkultur bed there are several variations, but I will discuss my own personal tips that have worked best for me over the years.

First, although you can place your branches and natural debris directly on top of the ground, I prefer to dig a trench. My reason for this is that it gives more depth to use, and also that it integrates the soil health better into the earth around the bed, making for a better garden space even years later if you decide to unearth the mound and plant on flat ground. By adding a trench, the whole bed becomes some sort of slow nutrient feed to not just your garden on top of the mound, but to the surrounding area including the sub-surface. Additionally, a trenched version will retain water better and not dry out. Building on top of the ground can also be more of an attraction to rodents who might start making their homes in the base logs of your mound. If you are trenched, there is more dirt and protection. Finally, if you dig a trench, you will be able to re-use that dirt on the bottom layers of your mound. Or, if it is already really good soil, it can make up the top layers of dirt too.

I start with a trench that is anywhere from eight inches to one foot deep, about five feet wide and 10-15 feet long. Since I spent the last 15 years in the hill country of Texas, it wasn’t easy to dig very deep because of all the limestone. It is fine if you have to dig around rocks a little and your trench is not completely uniform in shape. Bear in mind that your mound can be anywhere from a few feet to even as high as six or seven feet. The higher you are making the mound, the steeper it will be, given the same width. Therefore, a higher mound usually needs to have a wider base. Note that having a high mound that is protected from wind and water erosion until fully planted can create different microclimates that produce more of a polyculture and healthy garden. In fact, a high mound itself can serve as a good wind block for other parts of the garden.

Now it is time to layer your material. Starting from the base of your mound, in your trench, you generally want to put the largest pieces of wood that you have. These will take the longest to break down and will hold water at the base. It is very important you are not using green wood for any of your hugelkulture. Green wood will take much longer to break down and could arguably rob the soil around it of nitrogen for some time while it slowly decomposes. Ideally you want wood that is not only dried, but at least partially rotted. The more it is already aged and rotting, the better. Again, place the thickest and largest pieces of rotting wood at the bottom and then slowly start to pile on thinner and smaller pieces of dried and/or rotting wood. Many folks say it is best to use hardwood logs at the bottom and then use softer woods as you layer up. If you don’t have the luxury of selecting different hardness’s of old wood you might have available, do not worry about it. If you don’t have any larger old wood at all, then use what you have. Bark, smaller branches and clippings that have had time to dry out, dry leaves, dried grass clippings are all fine, but the larger the wood pieces can be at the bottom, the better.

Have a hose and spray nozzle nearby to thoroughly spray down each of these layers as you go. Spray down the old logs filling your trench. You can even spray down the trench before you put the logs in. Spray down the smaller wood pieces after you layer them up at least a foot over the ground level. Walk on top of all the mound to help pack it down and spray it down some more. I like to make sure that at a minimum the lower 2/3 of the mound is soaking wet as that will retain the water best and help with decomposition over the next few months.

As I work my way up the mound and I am at least a foot or two (depending on how high I want my mound to be, at least 50% - 60% of the final height) over the level of the ground, I like to add layers of old straw and some of the “greens” in composting along with the small dead wood pieces. This can include everything from kitchen vegetable scraps that you would put into your compost pile, to partially or fully composted matter from your compost pile. Burying vegetable scraps in or around a garden is sometimes referred to as “trench composting” and it works well if layered into the smaller wood pieces along with some dirt.

We have grown rabbits for food for years, and I like to use straw for their bedding. They like the straw as well because it’s easy to burrow in, nest with, etc. This rabbit straw mixed with rabbit manure has always made an excellent addition to my hügelkultur. Add layers of thin or small woody debris mixed with dirt on top of the mound at least a few feet over the ground level. This sort of “lasagna” layering approach to creating the above-ground layers of your mound allows a lot of potential nutrients to cycle inside the mound over the years.

Spray everything down again with water. This is now a great time to add in some earthworms. Worms are colony insects and do best if you put at least a handful together in each location throughout the length of the mound. Earthworms can be bought online or at your local garden store by the hundreds or thousands. They can even be grown at home. 2000 worms are more than enough for the dimension of the kind of mound I am discussing here. They will do best on top of the pre-wetted hay or dried grass clippings, then covered in dirt and with plenty of fresh kitchen scraps, rabbit poop, or other good worm food nearby. If you don’t have or want to put worms in the mound, that is fine too, but they will greatly speed up the decomposition and nutrient cycling of your hugelkultur mound. Whether you added worms or not, this is now the time to add about four to six inches of dirt across the whole mound. If possible, use the dirt you dug out from the initial trench for the mound. Spray it all down with water again until it is soaked through.

At this point the mound should be somewhere between two and three feet about the ground. This is where I like to mix up enough good topsoil to give myself at least three to four inches on top of the dirt we just put on to work with across the entire mound. Of course, you can buy ready-made topsoil, but it can be on the expensive side. If you are composting already and have some finished compost, this is a great time to use it and it can be part of a much less expensive DIY mix for basic topsoil. I usually mix roughly equal parts finished compost (humus – whether store bought or homemade), sand (and/or perlite), and peat moss to make my topsoil. I also throw in several handfuls of pea gravel per wheelbarrow load of topsoil to help with drainage. The peat moss is more acidic in pH (which you may want, depending on what you are growing), and the pea gravel down in central Texas usually has limestone (alkaline) in it which helps balance out the pH a little.

On the topic of drainage, a hugelkultur mound will usually have very good drainage, but as I mentioned we want the whole mound to settle for a while first before planting in it. Ideally, we want not only good drainage downward, but also some wicking upward of moisture. As the mound settles, one should have a nice balance of moisture retention in the woody parts of the mound, while also having some wicking effect upward with the wood, sand and even pea gravel. At the same time, it should have good moisture retention in its topsoil with the peat moss and compost, but also good drainage thanks to the sand and pea gravel.

Once you are ready to plant in your hügelkultur mound you can either plant seeds or seedlings. Using mulch material such as straw on top helps retain the moisture in the soil. If you are planting early in the year, it can also help protect your seeds or plants from colder temperatures. Adding in some logs, boards or even rocks or cinderblocks along the edges of the mound (where the mound hits level ground) will help mitigate any erosion, both while letting the mound settle as well as once it is planted. This also gives you some footing to more easily reach the top and upper sides of a mound for planting and harvesting.

You can water your hugelkultur garden from the top, with drip irrigation, or even use a root feeder or buried hose or PVC pipe in the same manner as a wicking bed. The logs, wood, and other plant material in the lower half of the mound will retain moisture for much longer than the upper soil and will both water and nourish your plants’ roots.