How to increase Soil Depth?

Good Afternoon Permies!

I have a simple question that has been bothering me for a while.

Can I increase soil depth by only utilizing organic matter?

My situation is I have a hillside that is being converted over to a pollinator garden. I have planted seeds towards the top of the slope and have created a small wood log berm at the bottom. The slope varies along the length of the hillside from a nice gradual drop to some sharp parts. I am currently hoarding this years leaf drop, leftover mulch and other organic material in this location and letting it degrade. If I consistently top off the hillside with organic material, will the slope improve or will the material just degrade into the existing mineral soil where it sits?

I want to avoid bringing in outside soil if I can, but if it is the only solution then it is what it is. I understand that my raised beds require topping off with compost due to organic material breaking up and utilization by plants but I don't know how much mass is leftover from the processes.

Time isn't an issue with this project, I'm not expecting changes for a while. This is some depleted soil that has suffered erosion and is currently being rejuvenated.

A lot of the mass you add as organic material will eventually break down (something will eat it and breathe it out as carbon dioxide and water) but if you, or the plants that grow there, keep adding new organic material on top, it won't go back to pure mineral soil. Depending on what plants grow there or what you add, soil depth might increase "by itself" for a while, but I suspect it would reach an equilibrium at some point, where as much is broken down as is added each year. Off the top of my head, the only situation in nature where soil depth increases constantly over longer periods of time due to accumulation of organic material is a peat bog or other type of swamp. And that's because the environment in a bog doesn't allow complete decomposition, as the amount of oxygen is extremely limited. Hardly what you want for your soil.

However, I think there might be a work-around. If you turn whatever woody biomass you can lay your hands on into biochar, that will increase soil depth without breaking down. Also, if memory serves, the Terra Preta soils of the Amazon can be repeatedly "mined" for soil, since for some reason the char and other ingredients added foster a microbiome that doesn't break down leaves and other debris all the way, but rather turns it into some compost-like stuff. No idea if it's possible to emulate that effect outside the Amazon, but even in the worst case your soil volume will increase by the volume of char you add.

Also, if the depth of soil is the important thing, you can (depending on your starting point) increase that quite a bit by making the soil less compact. And a key ingredient in making soil less compact is... organic material!

My simple solution would be to have lots of wood chips brought in and gather lots of bags of leaves off the curbs near you.

Making a lot of compost would help too.

Our quick solution has always been to have a load of sandy loam delivered.  That is also the expensive solution.

Timothy, I don't quite understand what your subsoil is. when you say "mineral soil" are you talking about clay?

How is the drainage? How does it react when it is very wet or very dry?

Dirt+ organic matters = soil. So yes, adding OM turns subsoil into rich top soil. What is the current condition of the area? For example, how deep is the top soil? What's the rough estimate of OM level? Any compaction? If you poke with a skewer, how deep can it go without bending?

A flower garden has different requirement from a production garden since many flowers are perennials and you are not taking biomass from it. While 5%OM is considered ideal for a vegetable garden, a flower garden can take less fertile soil.

If your area has decent soil, just plant away and add mulch on top. If the soil is poor and compacted, it's better to amend first by digging in lots of organic matters. Otherwise plants especially seedlings will be stunted and get out competed by weeds. Include a wide range of annuals and perennials, warm season and cool season plants, shallow rooted and deep rooted species so there will be lots of living roots in the soil. With the continuous influx of carbon from mulch and living roots, the fertile soil will grow deeper and deeper.

If it's a small area like a raised bed in the garden, trenching compost is the fastest way I've found.  When I start a garden, I usually get about 1/4 inch of soil or less, but by trenching compost I can increase the soil depth about 6 inches the first year and 10+ inches each year after.  But it works best in a concentrated area.

For larger areas, livestock is my favourite way to build soil.  The sheep add about 2-4" of soil to their pastures per year.  

But if those aren't options - look at your local nature.  What's her method for building soil?  
In many places this is mulch.  Leaves fall, decompose, soil happens.  Sometimes critters move things around to speed things up (digging).

green manure and chop'n'drop is also very popular in those climates.  Fukuoka talks about combining this and seed balls in his book One Straw Revolution.  But it requires a climate with rainfall at least once a month.  

Here, it's often about drying out organic matter to dust, letting it settle in hollow spots, then soddening them with excessive rainfall and cold for 6 months before going through a short growing season and then drying everything down in a drought for 6 months.  (mulch fails in our climate unless we add irrigation - but it's also not how nature makes soil here).

Since you mentioned a slope is terracing and intercropping with trees an option?  

Another success I've had building soil, is my keyhole garden.  I recently tore it apart as we needed the area to grow some trees, but it made a lot of gorgeous soil in a very short amount of time.  




there are too many options, so what I do when I want to improve soil, is to go for a walk in the local park.  Look at what nature is doing and think about what I can do to emulate it on my farm/garden with the least amount of effort on my part.  

Do you have a bunch of long lasting carbon sources to add to the system?  When doing the floating tomato gardens I want a material that is nearly all organic matter.  Manure got way to soggy.  Leaves etc are going to do a poor job simply because coming up with enough of them in any given year will be difficult.  Plus by themselves they will get way to soggy.  Twigs etc will hold things open so they stay moist not soggy  So branches as pilings, hugelkulture etc.  small sticks etc as retaining walls and leaves and small debris etc as the fill.  Add more wood in the form of inoculated biochar.  Then finally I would argue that you want to work up rather than down for the majority as you want a sponge at the bottom to catch all run off and grow the sponge up the hill.

Douglas Alpenstock wrote:Timothy, I don't quite understand what your subsoil is. when you say "mineral soil" are you talking about clay?

How is the drainage? How does it react when it is very wet or very dry?

Mineral soil as in the sand/silt/clay coming from rocks. There has been erosion of topsoil so it is a rocky/sandy mixture held together by some roots.

Ya'll are the best.

I believe the topsoil has been eroding for some time. I have a bunch of trees on the top of the hill who rooted along the slope. After 20 or so years you can see exposed roots going down the slope which has led me to believe erosion has been taking out the hillside slowly. This is worse in the steeper sections, which to me is expected.

I am going with a general three step approach at the moment and will see how it turns out.

I have already placed a wooden berm along the bottom that I will be reinforcing with some rough wooden stakes made from branches. I'm going to fill the bottom part of the hillside with organic material to create a 'sponge' kind of like what C. Letellier was getting at. The soil towards the bottom of the hill seems to have accumulated the larger aggregate of stone/gravel. I picked out the big ones and added them to a rock wall so far.

The upper portion of the hill, I have started to already seed as the soil is of better quality. I have already placed comfrey into the hillside with great success so now will be a mixture of annuals/perennials to get some roots down. I have some mulch at the top of the hillside to separate the lawn from the hill as well as to benefit the existing trees.

The upper part of the hill where it is flat is lined with Box Elder Trees. I am going to eventually cut them down to replace them with fruit/nut trees once the hillside is 'stable.' I think I might be able to get away with cutting them and leaving the stumps but I have to plan out my spacing for future trees. I might plant some fruit tree seeds for fun, see what takes, but that is after I complete a Perennial BB

Timothy,

Yesterday I went out and cleaned up my raised bed garden.  It had gotten pretty weedy so I took a hedge trimmer and cut things down to ground.  The bed itself was made of 2x10’s that I filled with wood chips and decomposed with Wine Caps about 5 years ago.  The beds are in terrible shape and were absolutely falling apart as I was cleaning up.  And as the edges of the beds fell off, behind them was hiding beautiful, rich, dark loamy looking soil.  Our soil is brown clay, but the piles of woodchips and all the fungal activity basically transformed the wood into dark, rich soil.

My vote is to pile up the wood chips as others have suggested.  It has worked absolute wonders for me.

Eric

As i understand your situation, adding stuff is still going to leave you in the same situation, unless you can slow the action of water (i assume water is the primary catalyst, not wind) causing the erosion.

I see your problem as less how to create soil (a far different topic) and more, how to prevent erosion.  It's not the adding of material that will solve your problem or help you with your goal, it's the prevention of erosion, be it from existing soil, or whatever you may add.

A couple years ago, I had an open pasture for horses with a slight downhill grade.  The problem was, the horses would walk along the fence to the point where the grass would not grow.  Over the course of a couple years, we wound up with a gulley that was over a foot deep at the deepest.

What I did was I took logs and laid them at an angle across the ruts, essentially creating a swale.  For my purposes, I only needed them to be a few feet long, and maybe 8" in diameter, one log laid at an approximate 45 degree angle along the path every 20', and then added soil to cover the logs, grading it out so everything was gently rolling, and reseeded.  That was several years ago.

Add whatever you want, it'll wash down.  The nature of organic matter is it is lighter than soil and will wash easier than the packed*, heavier soil.  Slow the movement of water, you'll slow or prevent the erosion.  Where you described where rocks accumulated is the first place on that slope where water slowed.  Heavier rocks dropped out first, and if you continue down hill, I'll bet you find places where other, lighter material accumulates.

*I do not mean to imply the soil is packed or compacted, just that it is not loose and airy.

I have an area where winter traffic kills the grass.  For reasons outside of my control, I can't pave it, even with gravel.  It has to remain a turf area in a courtyard with stones spaced throughout.  Looks nice, but it's pain to take care of.
When it is time to reseed, I must cover with some kind of erosion blanket, or all new grass seed will, at the first slight drizzle, wash out.  Once grown in, no problem.

I have garden areas where I used rocks placed in a line to keep the mulch from washing away.  It's all to slow the water.  Slow the water, things don't move far.

I just had a flash back to a conversation I had many years ago. A fellow homesteader was speaking with a small time construction company owner who was about to begin a new house with basement. He quickly got permission to show up a couple of days in advance and remove the top soil by hand. He ended up getting several pickup truck loads for the price of a few blisters.

I like this little segment that Sepp talks about his experience gardening on a hillside. I am now thinking about perhaps terracing a small bit. Even if it is just a smaller log bern halfway up the hill. Perhaps between my perennial garden and the expansion that I am going to now dump wood chips/chop and drop into.

I do like the idea that you present John! I have a few friends in the trades and I'm sure I might be able to score some halfway decent soil prior to a build. It is great to have a network you can tap into. My arborist buddy is glad to offload chips onto me when he does nearby work and I can use them.

Tim,

I re-read this thread and realized that my last post was slightly out of context owing to me having limited time to respond.  But I still have similar thoughts.

My basic answer to your question is that yes, you can definitely increase the depth of your soil by using organic matter, particularly in the manner you propose.

If you have access to abundant leaves, then use those, preferably chopped up and ground to fine shreds.  A leaf shredder works best, but a lawnmower will work very well too.

Another option is grass clippings, especially if you are reasonably certain that they are seed free.  Actually grass clippings and leaves make a very good combination.

Though wood chips might be hard to come by, they are fantastic.

Many years ago I had a huge pile of wood chips that I piled up 4’ in my garden bed over winter.  By spring when I spread them out it was difficult to discern where the bottom of the pile ended and the top of the soil began.  The two sort of merged together with the normally brown clay soil turning into something more like black, rich loam.  Actually the whole pile of chips had worms crawling throughout.  

The short version is “Yes” definitely pile on the organic matter and watch the soil depth increase and the soil characteristics improve.

Eric

I made the call to my arborist friend and it seems that my timing was kismet.

I have 10-20 yards of chips being dropped off sometime between today and Saturday. I need to get my stretches in and inflate my wheelbarrow tire because I am going to have some physical labor to do. I think it will be pretty neat because half the hillside is currently holding all of the fallen leaves from the property plus a bunch of chopped grass and now the other side will be wood chipped. It'll be interesting to see how they each develop.

I might as well order some King Stropharia spawn while I am at it. Nothing like some mycelium magic to really tie it all together.

Sounds like a plan Timothy!

Too bad that the time of year precludes you from planting any plants to grow along with the Stropharia, that’s how I like to grow them.  On the other hand, the main purpose of the plants is to provide some dappled shade and being winter, conditions are fine without shade.

At any rate, 10 yards is quite a load and I am sure that you will be plenty busy.  I once chipped up about 10 yards and moved it with a tractor and I was still surprised by how much time it took.  This could be a multi-day effort for you, but I am sure you are up to it.

Eric

how steep is your slope? Remember to build in the slowing of the water so all that wonderful biomass does not end up down at the base.

I am reading Mycelium Running by Paul Stamets and stumbled onto something that seems very on topic for this thread.

Talking about myco-remediation beds which are woodchips inoculated with spawn in order to restore lands that might be contaminated with ick.

It is mentioned in the book that for every 12" of woodchips laid out that roughly 1"-2" of soil would be created by their processing by biological and fungal processes.

This at least now gives me a kind of idea of how much work is going to go into this. Time to fire up the chipper and finally tackle that overgrown forsythia hedge it seems!

I have lots of slopes in my yard and was thinking about erosion as I read through all the posts on this thread. To add to what Dane said, one thing that has really worked for me is to halfway bury firewood in the soil, crossways so as to prevent erosion, in front on anything I plant on the slopes. I credit doing this to the success of my plants, and it has helped keep the soil and the mulch from falling down the hill, so it’s helped build up the soil. Plus, it looks cool!

I'm finding that the entire hillside turns out to be a great spot to hold ingredients for compost. Bulk wood chips, chicken litter, branches and sticks. The whole gambit.  

It is a slow and steady process, but I have seemed to reduce if not stopped the erosion I was experiencing so far. The spots that I do not have material on, I seeded heavily with a variety of cover plants to hold everything together. The materials are breaking down and slowly sinking, but I am adding more than are being reduced by natural processes at this point.

Due to the slow nature of the process, I'm more than likely going to start importing some local topsoil from a trusted vendor to reduce the worst of the sloped areas. I'm planning on creating a pumpkin patch on this hill because otherwise it is just a hub of pollinator plants which is fine in itself. I just really like sprawling vines.

Like others have said, I use small logs across the low areas, and as water travels over the area, debris starts to build up along the log face. Eventually the soil will be at the top of the log, repeat the process to add more soil level. This process does take some time but over the course of two years I was able to raise the soil level 6 in.

Another option, is to use the top of a tree that has been cut down or other large branch with lots of leaves to lay down into the low areas and the leaves and branches will start to collect debris and build that soil level up as well.

In another area I laid out a row of rocks across the flow area to create a small trap and then filled in with a variety of sticks twigs branches and other debris in front of the rocks to catch more silt and sand and debris and to build up that level of soil as well.

These free ideas do take a little bit of time to work but as soon as you put something in to stop or slow the path of water it will increase the debris collection and increase the level of the soil.

I'm still working on my hillside by incorporating some ideas from this thread. Thank you all who have contributed so far.

Excess organic matter has been spread and dropped off on the hillside. I also have incorporated planting cover crops/forage and letting them develop until a pre-determined size. I now will move a portable fencing around the hillside and let my chickens graze the area.

Keeping the hillside covered has significantly reduced if not stopped the erosion that I was seeing. Adding in wood and rock 'checks' on the hill has slowed down and captured debris. The worst of the divots and slope has started to gradually even out. It takes some time after adding the deep litter from the coop or woodchips for the material to properly pack down but it does after about a season. I'm most excited by the blooms of mushrooms that appear both on logs and through the soil. Pioneer plants have started to appear and expand through the area which used to be bare. I have taken to planting comfrey roots on the best parts of the hillside and chopping/dropping them when they get large enough to flop over.

There is a lot of work to still be done, but I expect I will be on the winning side of this 'struggle'.