Originally appeared in the Kildare Nationalist newspaper. Photo courtesy of Mark at Permaculture.com.au. 

A while back I wrote about how we built raised beds for our garden, and when they rotted, rebuilt them in brick. Many permaculture gardeners, however, build a different kind of raised bed, one that involves using no walls at all.

The technique, called hugelkultur (HOO-gul-kul-tur), has the advantage of being simple to understand and easy to make, and lasting a long time. Hugelkultur beds basically involve piling wood – usually dried logs of various sizes – into a single ridge, piling vegetation, cardboard or newspaper over that, and finally a layer of soil on top.

As the wood at the centre is slowly consumed by fungi, it absorbs and holds dozens of times its weight in water, creating a reservoir for the plant roots around it. As it decomposes it releases heat, extending the growing season. The decomposing wood, looking like a fine Swiss cheese under the soil, helps aerate the ground as well. Finally, as the wood breaks down into nutrients, its slow decay feeds the soil and anything growing on it.

Since the soil and garden plants are draped over logs, they also greatly increase the surface area for a garden, allowing gardeners to grow many more plants on the same ground. They also greatly increase the types of plants that can be grown near each other, as the top of the ridges will better suit sun-loving plants, while thirsty plants that can tolerate flooding will be more suited to the hollows between ridges. Such ridges are also an excellent way to stave off erosion and flooding, if you build them on a slope parallel to the side of the hill.

One risk in a hugelkultur is that the rotting wood might lock up nitrogen, so many gardeners prefer using large logs, buried deeply, so that the decay and nitrogen loss will be more gradual. Some also add high-nitrogen crops like nettles or comfrey over the logs and below the soil to offset the loss, or plant legumes or other nitrogen-fixing plants. Permaculture gardeners say that large ridges built over sizeable logs, or several logs, can offer a constant supply of nutrients for two decades.

Be careful what woods you plant; if it is aggressive coppice tree, like willow, make sure it is well dead and dried, or you’ll get willow sprouting from your ridge. Also, most texts on the subject warn against using woods loaded with natural pesticides, anti-fungal chemicals and the like – cedar, black walnut, black locust – but you’re not likely to find those in Ireland anyway.

Creating hugelkultur takes carbon out of the atmosphere in a few ways; it takes trees that are mostly carbon sucked out of the atmosphere, and sequesters them underground; and it encourages the growth of many plants that will, themselves, suck more carbon out of the air. In other words, it’s a win-win for the climate.

Hugelkultur beds can be built quite high, and some gardeners said they built theirs more than two metres tall, piling up the wood almost vertically and draping vegetation and soil over it. Some bolster the sides with pallets to keep them in place, but I wouldn’t recommend using them as the basis for the ridge, tempting as that might be – pallet wood is often sprayed with chemicals that you don’t want in your food.

Raised beds like this are more work at the beginning, but a lot less as time goes on, and can largely be left alone for years. Some gardeners recommend planting mostly perennials, which can keep producing crops year after year – and can keep building up the ridge as parts of the plants die off and become soil again. The plants’ roots also keep the soil in place, so rain doesn’t collapse the ridge.

Best of all, this garden uses scrap material that many people already have on their property, and are often trying to get rid of. Many of us clear brush or have to cut down trees or branches on our property, weeds and grass clippings they want to use, and spare soil not good enough for the regular garden. Hugelkultur uses all these things and combines them into something useful that can benefit your garden for years to come.