Hugel-what? If you’ve heard the term “hugelkultur” floating around the gardening world but aren’t 100% sure what it’s all about, then you’ve come to the right place! Let’s explore hugelkultur: what it is, the benefits it offers, potential drawbacks, the best wood and other materials to use in hugelkultur, which materials to avoid, and last but not least, how to make a hugelkultur garden bed.
What is Hugelkultur
Hugelkultur (pronounced hoogle-culture or hoogle-cool-tour) is a permaculture method of making garden beds by layering logs, branches, leaves, and other organic plant debris with compost and soil. In German, hugelkultur literally means “hill culture”. It has been practiced by natural farmers and gardeners around the world for centuries.
Traditionally, hugelkultur was primarily used to create mounded earthen garden beds at ground level, referred to as hugel beds or “hugelbeet”. Yet the concept is rapidly gaining popularity as a cost-effective way to fill raised garden beds, planter boxes, and containers too. Especially deep ones!
Benefits of Hugelkultur
- Hugelkultur mimics nature by design. Akin to a forest floor, the variety of decomposing natural material creates immense biodiversity in the soil.
- Rotting wood behaves much like a sponge: it absorbs, retains, and even releases water. Thus, hugelkultur garden beds require less water, ideal to conserve water and offset periods of drought.
- As wood and other natural materials decay over time, worms, beneficial bacteria, fungi, nematodes, microbes and other members of the soil food web work to create and release nutrients that feed plants. This type of effective nutrient release can occur for up to 20 years, depending on the density and type of materials used in the hugelkultur bed. The bed improves with time.
- Decomposing plant materials also generates some heat, which means the soil in hugel beds may warm up more quickly in spring to allow for earlier planting. This can also help extend the growing season come fall or winter, especially when coupled with hoops and row covers.
- Hugelkultur garden beds are budget-friendly! Filling large raised beds or planter boxes with soil and compost alone can get quite expensive. Filling the beds (at least part way) with collected natural materials is very cost-effective in comparison. Mounded hugel beds may be totally free to make.
- Hugelkultur garden beds are also eco-friendly. It’s a fantastic way to utilize and up-cycle plant “waste” around your property – rather than burning it or sending it to the landfill! Plus, creating garden beds from collected materials is more self-sufficient and sustainable than bringing outside materials into your garden. For example, bagged soil can create a lot of plastic waste! Whenever possible, get soil and compost delivered in bulk if large volumes are needed.
- Hugel beds are excellent at sequestering carbon. They’re also naturally aerated and don’t need turning or tilling.
- Hugelkultur is a great way to overcome poor native soil conditions, such as clay or rocky soil.
Potential Drawbacks of Hugelkultur
- Creating or filling garden beds with the hugelkultur method requires access to ample natural materials – a challenge for some urban or suburban gardeners.
- It requires a good deal of physical labor and effort to make traditional mounded hugel beds compared to standard in-ground garden plots.
- Hugelkultur beds may settle or sink down after the first year or so, so topping off with fresh soil and compost may be needed. Add soil and compost within the initial woody layers to reduce settling and air pockets.
- There is some risk of introducing pests or disease to your hugelkultur beds by using infected materials. For instance, we have abundant oak leaf litter on our property, but the leaves are almost always covered in mealybugs or whitefly, so I avoid using them in hugel beds. Termite-infested material poses a similar concern, especially when filling new wooden raised garden beds hugelkultur-style.
- Similarly, there is a risk of accidentally adding pesticides or herbicides to a hugelkultur garden – particularly if you’re using materials from an unknown source or not from your own property. Straw is a prime example, which is notoriously sprayed with herbicides and quite difficult to find organic.
- Since they’re prone to attract termites, it’s best to keep hugel beds at least 30 feet away from your home.
- Like other in-ground garden plots, it can be challenging to prevent burrowing pests like gophers or moles in traditional mounded hugelkultur beds. Gophers are a huge problem where we live, which is one of the primary reasons we garden in raised beds instead – and line the bottom of them with hardware cloth so they can’t get in.
- Tall, mounded hugel beds with sloped sides can be prone to sloughing and sliding around the edges. It may also be difficult to access, harvest, or tend to plants near the top or middle of the mound. Since plants sit higher off the ground, they’re more susceptible to the elements like whipping winds or frost.
- Young hugel beds may become nitrogen-deficient, leading to stunted plants. Keep reading below.
Does wood in hugelkultur beds steal nitrogen from the soil?
There is a notion that woody material (including logs, wood chips and branches) can “rob” nitrogen from soil. In reality, it doesn’t actually take any nitrogen away, but instead makes it temporarily unavailable for use by the plants – also referred to as nitrogen lock. Plants may be stunted as a result. Wood chips cause more noticeable nitrogen lock than large logs since wood chips offer significantly more surface area. Nitrogen lock can last for the first couple of years in a hugel bed, but then the nutrient becomes available to the plants again once.
However, it is easy to compensate by adding adequate soil and compost above the woody material for plants to grow in – explained more to follow. Use mild organic slow-release fertilizers to supplement additional nitrogen if needed. Growing nitrogen-fixing cover crops in the off season (such as fava beans, alfalfa, buckwheat or rye) is another great way to naturally add nitrogen back to the soil.
Materials to Use in Hugelkultur Garden Beds
- Logs or stumps, including fresh or rotting. Some that are already decaying is ideal! Read more about the pros and cons of different wood types below.
- Branches and sticks
- Wood chips, sawdust, wood ash
- Leaves or leaf mold
- Straw or hay
- Compost and manure
- Other organic yard and garden waste
- Brown paper bags
- Corn husks or stalks
- Fresh grass clippings or dry grass (be cautious of introducing weeds though)
- Chunks of sod, often removed from the site of the new hugel bed and placed grass-side down near the top of the mound after.
- Cardboard, especially as an initial weed-suppressing layer under the bottommost logs.
What type of wood is best for hugelkultur?
There is definitely some debate about what types of wood to use or avoid in hugelkultur garden beds. There are no hard fast “rules”. And don’t forget: the point is to make use of resources that are readily available to you!
Overall, hardwoods are ideal for hugelkultur. Logs from hardwood trees – including oak, apple, beech, alder, maple, sweetgum, ash, poplar and acacia – will decompose slowly and therefore supply nutrients to your hugel bed over a longer period of time. Yet soft woods such as pine, spruce, or fir will break down and release nutrients more quickly, giving everything a boost from the get-go! So, you can certainly use both. (But we’ll talk more about pine below.)
For the best results, use a variety of tree types and also a combination of fresh and already-rotting wood in a hugelkultur bed. Decaying wood will immediately begin to release nutrients and also inoculate the soil with beneficial microbes and fungi. Meanwhile, fresh wood will be there to support your plants over the long haul.
Materials to Avoid in Hugel Beds
Have you ever noticed that plants don’t grow well under some trees? Most permaculture resources recommend to avoid wood from allelopathic trees, or those that emit phytochemicals to suppress or even kill competing plant life around them.
Common examples of allelopathic trees include black walnut (the most notorious) as well as eucalyptus, sugar maple, sycamore, red oak, black locust, pepper, manzanita, American elm, and some pine species. However, all of these trees are allelopathic to varying degrees! Even more, they may only emit growth-inhibiting chemicals from certain parts of the tree, such as the roots or leaf litter only.
This guide from The University of Georgia breaks down various allelopathic trees into “strong”, “moderate” and “slight” categories and also denotes what part of the tree expresses allelopathy. Referencing the guide, it’d be wise to avoid logs and branches from trees that express moderate to strong allelopathy in their “rls” (root, leaf, and stem) pathways. I wouldn’t be as concerned about those that express it in their roots alone. Similarly, avoid using leaf litter from trees where that’s the main pathway.
Don’t use black locust because it will not decompose. Cedar and redwood also aren’t the best choices due to their high levels of tannins and natural rot-resistance. Last but not least, be sure that any species prone to suckering or sprouting (e.g. willow) are fully dead and dry before adding it to your hugel bed.
Can you use pine wood or pine needles in hugelkultur?
Yes, pine is fine to use in hugel beds! Especially in moderation (mixed with other wood types) and/or if it has been thoroughly dried and aged. Certain pine species are mildly to moderately allopathic, though in some instances that’s attributed to their needles rather than the wood itself.
Pine needles are known to be very acidic (with pH of 3.8) and therefore are often avoided for hugelkultur or compost. However, it’s a rampant garden myth that pine needles make soil more acidic! The University of New Hampshire clarifies that “pine needles themselves are acidic but do not have the capacity to appreciably lower the soil pH”. As pine needles decompose, they’re gradually neutralized by organisms in the soil.
How to Make a Hugel Bed (or Fill Raised Garden Beds Hugelkultur-Style)
Whether you’re creating a traditional mounded hugel bed or filling a raised garden bed (planter box) hugelkultur-style, start with the largest, most dense materials on the bottom. Begin with logs and stumps first, then layer in smaller branches and twigs, followed by leaves or straw. Finally, top it all off with several inches of well-aged compost and soil. Experts recommend incorporating a small amount of soil and compost to fill voids throughout the inner layers as well.
It’s important to provide at least 6 inches of soil (I recommend 10-12 inches) on top of the woody material. This offers adequate space for roots to grow and plants to thrive, especially in early years before the under-layers start to decompose. So, take that into consideration when filling raised garden beds or planter boxes. For instance, if your planter boxes are only a foot tall, add a fairly shallow layer of woody material at the bottom of the bed. The hugelkultur method is most helpful when raised beds are 16 inches or deeper.
In the “soil” layer, combine about 40% topsoil, 40% compost and 20% aeration additives – such as ⅜” lava rock, pumice, perlite, coarse sand, rice hulls, coco coir or peat moss. However, high-quality potting soil already contains plenty of aeration ingredients and perhaps some compost too. In that case, adjust your ratios accordingly (e.g. 70% potting soil plus 30% compost).
To create traditional mounded hugel beds, you can pile materials right at ground-level. Or, dig a shallow depression or trench (the size of the bed) to fill. Add the soil removed from the trench to the top of the mound at the end. To define the bed shape and add dimension, use branches along all sides to make a rough “frame”. Some permaculturists also use large rocks around the edges.
And that concludes this lesson on hugelkultur gardens.
As you can see, hugelkultur offers many benefits in the garden. It’s natural, cost-effective, repurposes waste, and pretty fun to boot! I hope you learned something new today, and feel excited to try hugelkultur in your garden too. Please feel free to ask any questions you may have in the comments below. If you found this information to be valuable, please consider pinning or sharing this post! Thank you very much for tuning in. Happy gathering and hilling!
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