Unwanted anaerobic decomposition in hugelkultur

I was reading through Jacke and Toensmeier's Edible Forest Gardening and came across this passage on page 362:

"People often build raised beds right over existing topsoil and vegetation, without considering what happens when organic matter gets buried and goes anaerobic. Such anaerobic layers impede water movement and root growth, limit the normal transfer of gases and nutrients in the soil profile, and produce toxic by-products such as ammonia and alcohol that reduce plant and soil organism health. The topsoil and organic matter should always stay on top, or your garden will drag a hidden weight behind it, slowing its performance for many years."

This made me pause. Hugel beds are constructed differently, but the same warnings apply, yeah? In our garden, our usual practice has been to dump kitchen scraps, maybe some unfinished compost, and whatever lush green vegetation was growing on the site before excavation (others would use turf or sod) directly onto the logs and woody debris, and then bury all of that thickly with soil, then mulch. Is this not creating the anaerobic conditions that the authors warn of? I saw some talk about this on the forum. Folks have pointed out that air pockets created by the coarseness of the woody debris would keep it oxygenated. And the steepness of the beds helps with aeration somehow? But I've also seen folks talk about packing the woody debris with dirt to stabilize the mounds, and I know that some of our hugel beds are not that steep. Now I'm thinking through all this again. Seems wise to make extra sure that aerobic conditions are present, or else compost the green stuff separately.

Any other thoughts?

I use buried wood beds and as far as I can tell, have never experienced anaerobic conditions. But I think I have a lot of worms and other critters moving around in the soil.

https://permies.com/t/52077/hugelkultur/Buried-Wood-Beds

Tyler Ludens wrote:I use buried wood beds and as far as I can tell, have never experienced anaerobic conditions. But I think I have a lot of worms and other critters moving around in the soil.

https://permies.com/t/52077/hugelkultur/Buried-Wood-Beds

Followed your link, the beds look beautiful, nice work! But it looks like you covered the wood directly with soil. My question referred to throwing fresh green material, like fresh weeds or unfinished compost, on top of the logs and then burying all of that with soil, which I've done. Wondering if the green stuff would anaerobically rot if buried like that.

I've covered all kinds of organic material with soil and haven't noticed any obvious anaerobic problem. Maybe I just wouldn't know what it looks like! I think if the material were really moist and green, not balanced greens and browns like unfinished compost, you might have it get slimey and nasty down there, but, I don't know if that would be a long-term problem. I usually improve my beds by putting fresh sheep manure, or fresh uncomposted chicken bedding w/poop on the bed and cover with soil, then plant right in that. The garden seems to be doing better every year.

I've seen this happen in my compost pile when I haven't mixed my grass clippings with another substance. That's actually the solution. Mix different materials together so that there isn't an airtight mat forming. Different materials decomposing at different rates combined with the activity and movements of the soil ecology will keep an anaerobic layer from forming.

This would also be another reason to not compact the soil in the bed. Compacting the soil will collapse the air pockets in the organic matter.

I've posted an exposition of this problem and the additional problem of Nitrogen Sequstration here:

https://permies.com/t/51382/hugelkultur/Geoff-Lawton-Results-Hugelkultur-Years#447043

I only use well rotted logs, I bet that helps. When I bought my place there was a large stack of firewood that prob stayed there for 20 years. It crumbles. Good stuff

Dave, I have the book you reference, and I've been using various methods of soil improvement over the years on hard alkaline clay. I have NEVER seen anaerobic conditions develop in any of the beds we've made, which includes hugel, lasagna, and double-dug. We have slow-draining soil, but it's never happened. Our first Hugelbeds were old logs buried in fresh horse manure, with aged compost on top. They performed well out of the gate, and are still healthy (it's been 6 years).

I think it's possible to create a peat-bog type situation, but it's nowhere near as easy as the book makes it seem, at least not in my experience. Unless you're building a raised bed on top of what would normally be a pond, I wouldn't think twice about going anaerobic.

Consider how many people use Earthtainers, or similar growing methods in tubs. That water with nutrients in the bottom goes anaerobic big-time, in only a few days, yet the plants stay healthy. I've pulled up tomato plants that had massive roots growing in the water itself, which had dropped to a pH of 4.5 due to anaerobic conditions. The plant was perfectly healthy.

Some of our best plots are lasagna beds over clay soil with wild oat and fillaree mats. We threw down fresh manure (lots of ammonia being produced) and covered with old straw, covered that with spent potting soil, and threw down radish seed. Those radishes punched holes into the clay through all the other stuff, and by the next year we were planting squash in the same spot, very productive.

I wouldn't worry about it at all!

After a number of years of having two large Hugelkulture berms in the back yard I am convinced that they have many positive attributes to support plant growth.
It would seem that the buried rotting wood should be a great environment for getting trees established.
We have a Cherry tree growing at the lowest end of one of the hugels and it is doing exceptionally well.

Thinking about various approaches to fruit tree planting, for 2021. I would like to try an approach of a drill hole 14" in diameter. Luckily I recently discovered that i can access a 3 point hitch post hole auger.

The current thoughts are:

Drill a hole 4 feet deep
place split wood in the bottom of the hole, for 2 to 2.5 feet and place sand around the wood for root pathways.
for the top 1.5 feet would place amended top soil, (sandy loam, with well aged manure) ...What other amendments should I consider?
Place bare rooted fruit trees in the amended soil zone.
stake and water (while having lots of patience to see them grow)
Is there any critical flaws to this approach? what could be done to value add this process, to increase the establishment period or increase the probability of success.
I have friends who are in the Cape Breton Fire Clay Zone who should benefit greatly with and approach like this.




Any comments for season tree growers or permaculture practitioners.


Is the wood too deep?

Will the wood be in an anerobic zone and therefore not work like a hugelkulture berm above ground?

Randy,

I would personally be concerned about the tree sinking as the wood rotted if planted directly above the buried wood. No great way to fix any sinking as trees don't like their trunks buried deeper.

I would also worry about the tree not wanting to send roots outside of the fertilized hole, which is the risk when with amending the planting hole. This is especially challenging in heavy soils which are hard for the roots to penetrate,  especially if the hole walls are smooth. The trees can get root bound.

My plan would be to backfill the tree hole with the excavated soil, roughing up the side walls of the hole first. Then when replacing soil put in the topsoil versus lower layers in the matching orders. Then amend the soil closer to the surface where the tree's feeder roots are, going out radially from the trunk to encourage the roots to grow outward.

Hi:

I can understand the possibility of root balling i guess.  

Some said the lower wood would stay in the saturated zone and therefore be anaerobic (slow) rotting and not more garden and mircobe friendly aerobic zone.

Interested in understanding that better.    i would think in my long big horizontal hugelkuture beds some of the wood would be in anaerobic conditions.

where is the line in a hugelkulture bed between aerobic and anaerobic...  is it bad of you have saturated soils in anaerobic conditions?