What to do with clay in hugel bed?

Hi.  Newbie and first post.  I am planning to dig several small hugel beds (4@ 2’x8’ and 1@ 2’x26’).   I have about 6 inches of top soil which includes leaves and wood chips I put down last fall to convert lawn to garden.  I’m scraping the “good stuff” aside and digging about 24” deep into the clay.  My plan was to remove the clay entirely and replace with rotting firewood/logs and other organic matter with the topsoil/leaf/chip blend that I scraped away on top, along with some composted manure.  Is this a good plan?  Seems to me that the thick clay would never break down and would fit back in the beds anyway.  Appreciate any guidance.

Hi Mark -
Please don't dig a big hole in the clay and put your hugel bed in it. Clay does not inherently drain well. When you dig a hole in clay, put plants in it and fill it with material other than the clay, it creates a bowl that holds in water and it doesn't drain well at all. Most plant roots detest being soggy so this situation is very unhealthy. And nothing ever remedies this situation other than replanting the plant correctly.  In fact, research shows that anytime you dig a hole in the ground to plant and you fill the hole with something other than native soil, the hole will not drain well.  Water does like to move from one type of medium to another.
Roots are the same way.  They will double back into the soil they were planted in instead of growing into the clay, creating a rootbound plant. This is the same reason why you should not put gravel on the bottom of a pot.
Instead, put your hugel bed on top of the clay.  Save your back. And, over time, it will break down and the released nutrients will add organic matter to the clay, loosen it up and make the microbes in the soil happy, thus improving the soil. You have a good start going with the leaves and wood chips you put down last fall.

Improving straight clay is a big, long term job. I dunno, there are a lot of moving parts here, but I think this could be a good approach. In the right place, I would consider doing the same thing.

What is the general climate? Local drainage profile? If it gets super wet, can you dig drains/pits to shunt away the excess water and prevent ponding?

P.S, welcome aboard Mark!

I also think it depends. I've got very heavy clay, I've made improvements in it as well as on top of it- but where I am it's tropical clay, which is full of soil life and consumes organic matter like gangbusters. As Douglas mentioned, I think a lot depends on whether there is actually any drainage or not.

Ok, so learn something new every day. I talked to some friends who have a huge hugel bed and they built it by digging a big hole in the ground and putiing in tree trunks first.  The soil around here does have a good portion of clay in it but does drain well.  The center of the bed is probably 3 feet about soil level and the whole thing is very fertile.  They use it as a vegetable bed.

Jen Swanson wrote:Ok, so learn something new every day. I talked to some friends who have a huge hugel bed and they built it by digging a big hole in the ground and putiing in tree trunks first.  The soil around here does have a good portion of clay in it but does drain well.  The center of the bed is probably 3 feet about soil level and the whole thing is very fertile.  They use it as a vegetable bed.

This is why it's so good to talk to locals!

The 2 totally above-ground hugel type beds I made are only working marginally. Granted they're not 7 ft tall which I'm told is what's required to hold moisture during a drought. I've also found it very hard to keep the wood covered. I've only got small areas to work with, and covering a hugel with compost rather than actual soil is totally not working.

I've had more success with hugel-style raised beds. The two recent ones are 30" high and have lots of wood at the bottom. However, one got mostly filled with compost and a bit of soil, and the second one I put a lot of clay soil around the logs at the bottom and in layers between the compost. The second one has performed better.

However, I also tried one situation where I dug a hole about 3 ft from where I wanted to plant a baby apple tree. I then filled the hole with wood, veggie scraps, dead chickens and chicken poop contaminated wood shavings. There is native soil between the apple tree hole and the compost hole. The worms in the compost are very happy. I have added a bit of water from rinsing out the compost bucket. We had a serious drought here this summer, and I only watered the baby apple once. I do think it's companion Seaberry didn't make it, but I find them hit and miss at the best of times.

I have two more larger apple trees I rescued that I'm desperate to get in the ground. I've decided to try the same approach.  Hubby used the back hoe to dig a hole. Our top soil is about an inch deep in that area, with clay soil and rocks compressed by the last ice age under it. I layered in dead birds, chunks of wood, sieved dirt that came out (only sieved to get the worst of the rocks out and break up the bigger chunks of clay), coffee sacks from brooders (ie inoculated with chicken shit), and fresh horse shit from a friend. Before it started shrinking from decomposition, the pile was about 4 feet above ground level at the top. I had to get creative to keep its sides straighter than gravity wanted it to be (the coffee sacks help with that). My plan is to plant stuff on the mound that is short-lived as it will shrink a lot, and to plant the tree just down-slope of it. I've now started a second hole where I'm trying the same approach.

It will be really interesting to compare how the first beds vs the hugel-style raised beds, vs the trees with the hugel mounds do over time. Adapting various permaculture techniques to ones specific eco-system takes some trial and error. I'm thinking the two first beds really need some of the clay subsoil added to them along with some more finished compost this year.

Jen Swanson wrote:Hi Mark -
Please don't dig a big hole in the clay and put your hugel bed in it. Clay does not inherently drain well. When you dig a hole in clay, put plants in it and fill it with material other than the clay, it creates a bowl that holds in water and it doesn't drain well at all. Most plant roots detest being soggy so this situation is very unhealthy. And nothing ever remedies this situation other than replanting the plant correctly.  In fact, research shows that anytime you dig a hole in the ground to plant and you fill the hole with something other than native soil, the hole will not drain well.  Water does like to move from one type of medium to another.
Roots are the same way.  They will double back into the soil they were planted in instead of growing into the clay, creating a rootbound plant. This is the same reason why you should not put gravel on the bottom of a pot.
Instead, put your hugel bed on top of the clay.  Save your back. And, over time, it will break down and the released nutrients will add organic matter to the clay, loosen it up and make the microbes in the soil happy, thus improving the soil. You have a good start going with the leaves and wood chips you put down last fall.

Great points.  I had not considered that I would be creating bowls with the problems you highlight. I am in the mid-Atlantic U.S. zone 7b.  Heavy clay.  I have a relatively small area where I am expanding my growing and putting all of my new beds.  I really wanted to do in-ground “hugel.  My finished beds will only be slightly raised.  I will border them with logs.  I have one bed that I have been conventionally gardening for years about 18” high (6x6 lumber). I would like to do all raises beds but don’t really want to use pressure treated 6x6 any more and don’t have materials otherwise.
My plan for the surrounding clay where I will establish new beds is to “break” the soil once or twice a year with a broad fork.  This will aerate to about 14” deep.  My thinking was that this would improve the surrounding clay soil over time.  Now I’m thinking this may not be sufficient given what you laid out for me.  Any thoughts on the approach I was considering with the broad fork?  I live in a suburban neighborhood and don’t want to do hugel mounds for aesthetic reasons.  
Thanks for your great advice.

Mark Sanford wrote:

I would like to do all raises beds but don’t really want to use pressure treated 6x6 any more and don’t have materials otherwise.

I agree totally about not using pressure treated. There are some threads such as this one ( https://permies.com/t/163796/Ideas-Trellis-Gardening ) with pictures of raised bed alternatives. If you have a local free-cycle type of program/website you may be able to gather materials slowly. I've got almost enough breeze blocks to build a second breeze-block bed two blocks high which have come from a gentleman who knew I wanted more and was able to trade cheaply for them. My new 30" high beds I mentioned were built out of HT (heat treated) packing skids. I find them time consuming to build, but the only expense was the brackets for the corners and the gas to collect the skids from a hardware store less than 5 km away. We happen to own a utility trailer though, so if you don't have access to something like that or a pick-up truck, or a really good cargo bike, that's a problem. The nice thing about the way I made my skid beds is that they look very nice, which in an urban area is a plus. Not that you can actually see much of them at the moment - with the heat this summer, the beds have tomatoes and tomatillo plants hanging off the sides to the point I can hardly get past!

So far as your question here:

My plan for the surrounding clay where I will establish new beds is to “break” the soil once or twice a year with a broad fork.  This will aerate to about 14” deep.  My thinking was that this would improve the surrounding clay soil over time.  Now I’m thinking this may not be sufficient given what you laid out for me.

What is the slope of your land and where and how does water currently drain?  What have people done in your area that have *really* wonderful gardens?

Douglas Alpenstock wrote:Improving straight clay is a big, long term job. I dunno, there are a lot of moving parts here, but I think this could be a good approach. In the right place, I would consider doing the same thing.

What is the general climate? Local drainage profile? If it gets super wet, can you dig drains/pits to shunt away the excess water and prevent ponding?

P.S, welcome aboard Mark!

So, I proceeded with digging out the clay in the hole I had already started to a depth at about 2 feet.  Really thick gray clay that drains very slowly.  I may experience the problems share in the thread - the bowl effect.  I wanted to do three beds (originally 4, but three fit best, but did not for two reasons.  (1) THE.CLAY.IS.THICK! - but I wanted to try it in one bed so seep how it works. And (2) it is more work than I can get done.

So, I finished three beds and will put some pics if I can figure out how.

I concevert this area from lawn last fall by placeing cardboard, 6-8” of chopped leaves, and 4-6 inches of wood chips.  This year I planted squash and cakes in the area by digging holes and putting in good soil/compost to form mounds.  I did not have any success which I thought was odd.  I think I got some sort of deseSe in the plants.   It sure. Cubes in the nearby bed did well but not the squash in the same bed.  

So for the beds, the Bed in the foreground is a buried hugel.  I’m using logs to border all three beds so I do have a slightly raised bed.  The other two I just placed logs on top of the leaves/chips I laid down last year.  I topped  all the beds with chopped leaves, aged composted manure, leaf mold, chopped hosta, and finally leaf mold again.  All layers about 2” or so.  I will put more chopped leaves on top this fall.  I am hoping these beds will be in real good shape in the spring and may try to put some garlic in this fall.  I did my first garlic last fall and had a decent crop.

I added a pick of my main raised bed (6.5’ x 24’).  I put this bed in 5 or 6 years ago.  I got the permit bug last year and did the chopped leaves and chips on the two short sides of the bed and the down slope long side.  Total area including the main be is probably near 600 sq/ft.  I was initially going to just kind of plant randomly in the chip area, but after my squash and cake failure decided to use logs for raised beds and focus on building soil.

I have also upped my compost/leaf mold production and started vermicomposting to feed these beds.  

Wanted to add a couple more pics of my "hugel" experiment.

These two show shallow trenches I dug in the paths between my new raised beds.  I fill these trenches with sticks, green stuff, and topped with wood chips.  I also just put wood chips in the path ways to about 8-10 depth.  Not quite done - need probably 5 more yards o complete this space.

Trying to determine if I want to try to grow wine cap mushrooms in the wood chips.