Hügelkultur

A hügelkultur mound has three slightly different growing areas to accommodate various plants. As the contents within the mound begin to decompose, the quality of the soil will change as well. So, we will look at plants that grow in these three spaces over time to adjust to the changing environment within the soil of the hügelkultur.

Top of the Mound
This part receives the most sunlight and, being at the top, is typically the driest area. In the first year or two, the wood will absorb most of the water, so it will be necessary to keep it watered. But as time passes, it will become better at retaining water and suitable for a wider variety of plants.

Years 1-3: Drought Tolerant Plants (thyme, rosemary, oregano, sage), Hardy Flowers (marigolds, nasturtiums, cosmos), Vining Crops (melons, gourds)

Years 3+: Perennial Herbs (lavender, mint, lemon balm), Flowering Plants (sunflowers, echinacea), Shallow Rooted Vegetables (carrots, radishes, beets)

Sides of the Mound
Depending on the orientation of the mound, the sides may receive a lot or a little sunlight. The sides tend to hold more moisture than the top. They are more prone to erosion in the initial years, so ground covers work well as living mulch to keep the sides intact. Since decomposing wood initially takes a lot of nitrogen, this is a good place to plant nitrogen fixers to replenish the soil. Over time, root systems and settling of the mound make it more stable, and the risk of erosion diminishes.

Years 1-3: Nitrogen Fixers (clover, lupines), Hardy Vegetables (zucchini, squash, pumpkin), Cover (strawberry, alfalfa, peas, vetch)

Years 3+: Vegetables (tomatoes, peppers, cucumbers), Perennials (daylilies, black-eyed susans), Herbs (parsley, basil, dill)

Bottom of Mound
Water tends to accumulate at the bottom, making this area wet, cool, and often shady (depending on orientation). Plants that love water do well here. Keep watch that the area doesn't get waterlogged, though. If it does, add some organic matter, such as coco coir, perlite, or vermiculite, to help create aeration. Or focus on plants that require very wet environments.

Years 1-3: Greens (lettuce, spinach, kale, swiss chard), Hardy Roots (turnips, onions, garlic), Moisture Loving Flowers (begonias, coleus)

Years 3+: Fruit (blueberries, raspberries, strawberries), Nutrient Demanding (corn, broccoli, cauliflower), Deep Rooted (rhubarb, asparagus, horseradish)

There aren't many restrictions for size, shape, length, and placement regarding a hügelkultur mound, but your choices will have consequences because, after all, we are up against nature. Here are some things to consider when designing your hügelkultur bed.

Height: The bed will shrink over time as it decomposes, so even if it initially looks pretty tall, it won't stay that way. A bed should be at least 2-4 feet tall - you can go up to 6 feet if you have the materials. The taller it is, the easier it is to reach.

Width: Aim for a width of about 3-5 feet. This will vary based on your space and materials.

Length: It can be as long as you want, but generally, they are about 6-8 feet long.

Slope: A steep hügelkultur can increase surface area, allow roots to grow deeper, enhance the microclimates, and improve drainage, but it also increases the likelihood of erosion, so be sure to place some borders and mulch on the surface.

Shape: Keep it simple with a straight line or add some curves. They can be made into any shape, such as a keyhole bed.

Microclimates: Consider the movement of the sun with your hügelkultur. If it runs north to south, one side will get morning sun, and the other will get evening sun. If it runs east to west, one side will always be shaded, and one side will be in the sun all day. Either configuration will work but affect what can be planted on either side.

Location: Consider obstructions that are or will be nearby that may block the sun, wind, or water flow. Elevation can also affect the amount of water the mound absorbs; lower elevation will provide more water absorption. Try to orient the mound perpendicular to the water flow so that water stops at the bed. Also, note the wind patterns in the area throughout the year.

Depth: To capture more water runoff, a mound can be placed directly on the ground's surface or in a trench, though this will lower the mound's overall height.

Borders: Materials like stone, brick, wood, and straw can help hold the shape and prevent erosion. Depending on the extent of coverage, they can also provide insulation.

Timing: Any time of year is acceptable, but if you set it up in the fall or winter, it will have time to begin decomposition and settle before planting in early spring.

Variation: This same concept can also be used in a tall raised bed. When you have a lot of space to fill, use the same layering technique to build a healthy soil bed.

Not all wood is created equal. In this case, hardwoods are the best option. Alder, Apple, Aspen, Birch, Cottonwood, Maple, Oak, Poplar, and Willow all make good choices.

The following wood types should be used with caution and moderation. If used, the wood should be well-rotted beforehand and placed at the bottom of the pile so it has more time to break down before plants reach it.

Wood resistant to decay often has antimicrobial and antifungal properties and resists the efforts of decomposers. Examples include cedar, juniper, osage orange, red mulberry, cypress, and yew.

Allelopathic wood releases chemicals that can inhibit the growth of other plants. Walnut and black locust should be avoided altogether. Other woods include eucalyptus, redwood, pine, and cedar.

Tannic woods, such as oak, chestnut, hemlock, spruce, and redwood, can make the soil slightly acidic.

Resinous Woods, such as pine, fir, spruce, cedar, and juniper, may contain compounds that slow the growth of other plants and are slow to decay.

Wood can be added in stumps, logs, twigs, and sticks. Each size will decompose at different rates. Woods chips can also be used for faster decomposition. Rotted wood is better than slightly aged wood because it won't consume as much nitrogen in the first year. Also, wood that isn't dead has the possibility of sprouting.

Aside from topsoil and compost, other things can be added to the pile.

Amendments

• Manure | nitrogen
• Worm Castings | nutrients
• Coco Coir | aeration & moisture retention
• Alfalfa Meal | nitrogen & trace minerals
• Bone Meal | phosphorus & calcium
• Blood Meal | nitrogen, lower pH
• Fish Emulsion/Fish Meal | balanced nitrogen, phosphorus & potassium
• Kelp Meal/Seaweed | potassium & micronutrients
• Leaf Mold | soil structure & water retention
• Grass Clippings | nitrogen
• Pine Needles | lowers pH
• Agricultural Lime | raises pH, calcium & magnesium
• Gypsum | calcium without altering pH
• Rock Phosphate | long-term phosphorus
• Greensand | potassium & trace minerals
• Azomite | trace minerals
• Dolomite Lime | raises pH
• Sulfur | lowers pH, sulfur
• Perlite | drainage & aeration
• Vermiculite | retains moisture
• Zeolite | nutrient retention
• Basalt Rock Dust | slow-releasing minerals
• Biochar | carbon, nutrient retention
• Epsom Salt | magnesium & sulfur
• Crushed Oyster Shells | calcium, raises pH
• Granite Dust | slow-releasing potassium

The top of the hügelkultur can be layered with straw or surrounded with straw bales to create insulation.