What it is
A raised bed built over a core of buried wood. German for "mound culture."
Sepp Holzer made it famous. He terraced the Krameterhof at 1,000 m in the Austrian Alps. No irrigation. Stone fruit on slopes most farmers wrote off.
The idea is older than him. Central European gardeners have been burying logs under garden beds for centuries.
Why it works
Wood rots slowly underground. As it breaks down, it stores water and feeds plants.
A cubic meter of well-rotted wood can hold up to 300 liters of water. Rain soaks in. Capillary action and fungal hyphae move it back up to the root zone during dry spells.
The fungi do the work. Soft-rot species colonize first, then white-rot and brown-rot fungi crack the lignin. They release phosphorus, potassium, calcium, and trace minerals as they digest. Same mycorrhizal networks that feed native oaks in a forest floor.
Decomposition also generates heat for the first year or two. Spring planting comes earlier. By year three, the mound is mature humus that holds water through drought.
Build it
Dig a trench 30 cm deep, 1.5 to 2 m wide. Save the soil. Save the sod, grass-side down.
Orient east-west for a warm south face, north-south for even light.
Stack your biggest hardwood logs in the trench. 15 to 30 cm in diameter is the sweet spot. Pack the gaps with branches, twigs, wood chips.
Then layer. Fresh grass clippings, manure, or green leaves go next. Nitrogen for the fungi. Then half-finished compost or leaf mould. Then at least 10 to 15 cm of reserved topsoil on top.
Finished height: 1 to 1.5 m. It will settle by a third in year one.
Soak the whole thing. Logs need saturation before they start working as a sponge. Some builders pre-soak logs in a pond for two weeks to seed the fungi early.
Pick the right wood
Alder, apple, poplar, birch, maple, oak. Alder is best because it fixes nitrogen.
Skip black walnut. The juglone kills tomatoes, peppers, and most nightshades.
Skip cedar and black locust. They resist rot, which is the opposite of what you want here.
Pine and softwoods work, but they break down fast and acidify the mound for a season. Mix them with hardwoods.
Don't build from chips alone. The logs are the backbone. Chips and branches fill gaps and feed plants in the early years.
Tend it
Year one, plant for low nitrogen. The wood ties it up while the bacteria get going. Squash, potatoes, beans, peas. The same legumes that pull their weight in a companion planting guild.
Year two, the balance flips. Fungal breakdown releases more than it consumes. Widen the rotation.
Year three onward, this is the most fertile bed on the site. Tomatoes, peppers, melons. No added fertilizer.
Water heavily the first season. After that, most mounds need little to no irrigation, even through dry spells.
Keep slopes between 30 and 40 degrees. Steeper than 45 erodes before plants establish. Mulch the surface with straw or chips after planting.
A mature mound makes a strong skeleton for a food forest.
When it goes wrong
Yellow leaves in year one usually mean nitrogen lockup. Side-dress with compost or aged manure.
Sinkholes after heavy rain mean the logs weren't packed tight. Top up with soil and mulch.
Steep faces washing out in storms mean too sharp a slope. Pull the angle back, replant.