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Hugelkultur structure

Hugelkulture Garden Bed

Down the back of my yard there was an ugly pile of old rotting stumps and logs. They had been waiting patiently for me to make a hugelkultur garden bed and this weekend it was time.

What is a hugelkultur garden bed

The word “Hugelkultur” is a german word which means “hill culture”. The technique involves putting logs and branches underneath the soil and growing your plants on top. This has several advantages.

  • As the logs break down they soften and act like a giant sponge at the base of your garden supplying water to your plants even during the driest of weather. Your plants are passively irrigated but never overwatered as they are able to draw the water from the rotting logs when they require it.
  • As the logs decompose they create a healthy ecosystem of fungi and bacteria which provide nutrients to your garden plants.
  • A hilled garden can create various ecosystems around the mound. Shade loving plants can be planted to the South (in the Southern hemisphere); plants which prefer things hot and dry like your Mediterranean’s can be planted to the West; those which like some sunlight but can be scalded by the hot Western sun can be planted to the East; and plants which are happiest in all day sunshine can go to the north.
  • The garden bed improves over time.

A hugelkultur bed should be used exclusively for annuals in the early years. As the logs break down and the air spaces between the buried logs fill, the garden bed will sink considerably. This is not suitable for perennials whose root systems will be damaged as the mound settles. In order to benefit perennials with this system you would plant them around the edges of the hugelkultur so they can extend their roots towards the rotting logs while remaining in stable soil.

About the logs

The larger the log the better. 300mm diameter or more is best but smaller is fine too if that is all you have. A mix of hardwoods, softwood, newly felled and weathered logs give the best all round short and long term results. Softwoods and older partially rotten logs give faster results, whereas hardwoods and fresh logs take longer to start working but give better long-term results.

Hugelkultur variations

Traditionally, a hugelkultur bed is simply built as a huge pile directly on the ground, but if you prefer the look of typical raised garden beds then you can build a raised bed and put logs in the bottom and your garden soil on top of this. No one will ever know that your raised garden bed is actually a hugelkultur bed. A sunken hugelkultur bed can also be built however this must be carefully planned and understood as this may be a disaster waiting to happen. If your soil holds water long enough for the buried logs to start floating, what is going to happen to your garden bed on top? A sunken hugelkultur bed must take into consideration: the soil type (how fast it drains), how much rain might be expected in a heavy rainfall event, the type of wood being used, the age of wood being used, and the depth of the hole. All of these things play a part in the design of a sunken hugelkultur garden. Suffice to say, a sunken hugelkultur bed is a benefit in some situations, in particular when the logs need additional time to soak up water – such as on a slope when the rain runs off too quickly and in drier environments. I chose to sink my hugelkulture bed due to the fact that this area of my garden has no swales to hydrate the soil and as I never water my food forest I needed to hold extra water in this area when it rains. I was originally going to dig a soakage basin but then decided to combine it with the hugelkultur bed.

How to

  1. Place your largest logs at the bottom of the designated garden area. If you leave a gap of 25mm to 50mm in between each log you will be able to more easily fill the voids between logs and minimize sinking of the bed.
  2. Fill the spaces in between the logs with smaller logs and branches and then backfill all the gaps with soil. Try not to leave any air pockets underneath the logs.
  3. Place smaller logs and branches on top of the bottom layer. If the wood is fresh then adding a high nitrogen component (such as freshly cut grass, chicken manure or Blood & Bone) will help alleviate nitrogen draw down issues. Backfill all the gaps and holes with soil.
  4. Top the entire planting area with approximately 150mm of good quality planting medium (top soil, compost, manure, etc) and mulch well.

Since my “logs” where mostly odd-shaped tree stumps with roots jutting out in all directions I was unable to follow the above method perfectly so my hugelkultur bed is going to sink A LOT as all the air pockets fill. For this reason I will not be planting into my garden right away but will give it extra time to settle. I also didn’t worry about removing the clumps of grass from my soil so I will solarise the mound with some black plastic in order to kill off the grass before planting it out.

You will need to initially water your hugelkultur garden while the logs are still absorbing moisture, especially if you have used freshly fallen logs. However, gradually the logs underneath will become more and more sponge-like and supplementary watering will taper off. How can you not love a garden that just gets better and better over time!

Now run outside and create your oasis!