Pit and Mound Gardening

Hang out in sustainability circles for any length of time and you will notice a distinct antipathy towards traditional vegetable gardening. It ruins the soil; it is dependent on inputs; it eschews perrenial plants. It is un-natural. And in most cases that is all true.  But there are some real truths that this attitude can gloss over.  First, annual vegetable gardens are wicked productive – easily a pound or more per sq ft.  Second, the vast majority of us are used to eating food grown in annual vegetable gardens and food habits are extremely difficult to change – they are a integral part of our living culture and that changes slowly;  I am much more likely to eat potatoes than skirret or sunchokes, no matter what the permaculture books tell me.  Third, its gonna take YEARS for your multi story permaculture forest garden to start producing much of anything.  For certain, eventually it will outpace your annual gardens in productivity, but that is a decade or more out.  Until then, the 25#’s of harvest per tomato plant is gonna make you and your larder a lot happier.

So whats a suburban homesteader to do?  I’ve read thousands of pages on sustainable vegetable gardening – fantastic books from John Jeavons, Elliot Coleman, and many more that have inspired and intrigued me to the possibilities of vegetable gardens.  I’ve also read thousands of pages on ecology and soil science that contradict so very much of what those masters and mistresses have to say; tilling is very rough on the soil.  I want to have healthy soil, but I also need and intend to have a large canning garden for years to come.  Mulch Gardening like Ruth Stout’s “No – Work” garden and Lee Reich’s Weedless Gardening makes a great step towards integrating the two philosophies by removing much of the tilling.  Word to the wise though on this – Ruth Stout gardened conventionally for over 7 seasons before switching to no-till.  It takes a long time to build up your soils and you also need to irradiate persistent perennial weeds like quack/couch grass, sow thistle, and the like if you have them on site.  No till gardening is a journey, not a destination!

Bolstered by some impressive results from 2009, I mulched heavily this year and was very impressed with the reduced weed and irrigation inputs.  But the garden was still flat and that bothered me.  So at the market garden I tried a new technique that I want to explore Whole Hog in 2011.  Essentially it is based on a side bar blurb in Chapter 12 of David Blume’s epic opus Alcohol Can Be a Gas. Now a book on homebrewed energy revolutions is not a place one would expect to have an epiphany on vegetable gardening, but David is a die hard permaculturist so its all connected.  His idea was to dig trenches under your paths, fill them with mulch, and then use these mulch paths to breed up trillions of red worms to function stack a “wasted” space in the garden.  This idea worked wonders at the farm – with the beds I used this technique out producing my conventional beds by 20-50%.  As the season went on, I gave it more and more thought and always paid special attention to those two beds – digging and poking around as I tended to them.    My findings in short were these:

  • Mulched Trenches improved drainage -essentially turning the planted areas into raised beds
  • Mulched Trenches improved water retention – the mulch acted like a sponge, holding water for weeks and weeks between rains keeping a higher water table within reach of the annuals
  • As hoped, Mulched Trenches foster just ridiculous amounts of fungus.  My hope was that even with the soil intrusion in the beds from potato harvest the fungus would live on in the paths to re-innoculate the soil for the next season.  The mycelium was often inches thick and brilliant white to the naked eye.  Bingo!
  • Thanks to the moisture and fungus, the Mulched Trenches are havens for earthworms, even if you don’t plant worms in them, they will be there soon enough.
  • Within only 3 months, a 1/8″ (3 mm) layer of humus formed under the straw that mulched the potatoes and was clearly evident to the naked eye when harvesting.  That is very impressive soil building in such a short time.  Now, this was on incredibly microbially rich soil that has been farmed organically for 20 years so your results may vary, but it is no wonder why straw mulch gardening works.  You are truly “uppening” your soils!

All of this really coalesced with the epiphany that  my Mulched Trenches essentially mimic “pit and mound” topography in old growth forests and were creating all kinds of interesting micro climates for soil fauna and plant roots to exploit.  Wait a minute – the reviled and ecologically barren annual vegetable garden was starting to sound a lot like permaculture!  I was on to something.

With that in mind, I set out to integrate these learnings into my freshly “pimped out” garden as I prepped it for the 2011 season.   The layout will be a 1′ Mulched Trench on each side of 30″ growing beds.  Now that is a lot of path, and purists will give me hell for that.  Whatever!  To manage a 1100 sq ft garden, be a husband, father, and still work a full time job and do all my other projects if I can’t get into my garden easily and efficiently it will turn into a mess faster than you can say “fundamentalist”.   I plant in straight lines – it may not be efficient in space, but it is incredibly efficient in time and labor – we need to factor those things into our plans too.  Mandalas are great, but they’re not for me.  While digging the trenches the soil was piled up onto the 30″ growing beds – mimicking a “double dug” bed.  On top of this I applied .5-1″ of compost and topped that with 4″ of straw with a nod to Ruth Stout.  Here are some pics:

1' deep and about 1' wide - basically dig a trench with a spade and pile it onto your garden bed. As these paths are to be semi permanent I pulled some lines to keep me honest.

Once the trench was dug and emptied, I filled it with chips. I like to use fresh chips with leaves in it if I can - the nitrogen helps to feed the soil ecosystem. Tamp the chips well (walk on them) and mound them slightly as they settle. I aimed to keep them about level with the top of the growing beds. As the trenches are 3/4 full, rake the growing beds flat to get them back to 30" width and then top the trenches off. Figure a cu ft per running foot - these beds are 32' (9.7 m) long so it takes over a cu yard each.

After the growing beds are raked flat, I put down a .5" (13mm) layer of compost which is enough to cover the soil. More is better, but the most important thing is to inoculate the bed with soil bacteria which will munch slowly on the straw all winter and add some humus.

At this point the beds are built and the straw is laid down.  That is all pretty straight forward.  But before I sign off I would like to show some examples of just WHY this is so important:

This was from one of the chipped paths from this summer's garden. These chips were only 4 months old - just LOOK at that fungal growth!

This is also  my answer to any concerns about “locking up nitrogen” by adding this much carbon to the soil.  The fungus is working like crazy to break it down, plus the soil in the growing beds is normal and the nitrogen concerns will only be in the paths or just next to them.  And once the plant roots start exchanging sugars with the path fungus the soil economy will go bonkers to the benefit of your pantry through increased yields.  Just so you understand that this wasn’t an isolated  shot her are some more pics — all from the same row!

Almost 4" thick - the fungal net was already reaching well below the chip layer. Again - this is 4 months or less of growth!

These fungal nets capture nutrients and water reducing leaching and feed worms (see him?) and other soil fauna. Fantastic!

I am an unabashed Soil Geek, but these discoveries had me beside myself, jumping, hollering, and dragging my wife and kids out to see the bounty growing under my paths. Wow.

So there it is, my Pit and Mound gardening method.  Essentially I am taking straw mulch gardening -the tomatoes and other big plants will grow right into this mulch- and taking it up a notch with a healthy dose of soil ecology by fostering fungus, worms and all their buddies in the “permanent” paths.  This also reduces labor by increasing the gardens ability to self irrigate by essentially creating contour swales next to each bed.

Time will tell how much of an impact this will have.  But I do know that some of the best soils on my property are found UNDER my wood chip paths, humus is formed from carbon after all.  Any question about the efficacy of fungus to make soils is erased by going out to a nearby woods and rummaging under the leaves – its amazing.  In addition to the paths, the growing beds now more precisely mimic a natural soil structure – beneath my garden is the sub soil, then a foot of top soil, the the “duff” layer of partially decomposed material in the compost I applied, and topped with raw organic matter in the mulch.  EXACTLY the same strata you will see in a prairie or forest.   Its still a veggie bed, but we’re a helluva lot closer to building more sustaining system as it holds water, suppresses weeds, and builds soil and soil ecosystems.

Be the Change!

-Rob

Midden L’eau Chaude: The Big Build

Load #2 being dumped for a total of about 17 cu yards (13 cu m). Let's do this.

Last summer I built the Methane Midden which was inspired by Jean Pain’s epic work in 1970 France.    It was big, it was a little insane, and ultimately it didn’t work. Don’t get me wrong – it made a syck amount of compost, but it failed to meet my goals of also producing methane and hot water.  Time to do better.  The second Midden will focus on Hot Water (L’eau Chaude) with a dedicated heat exchanger and will be even larger.  Not only that, but I wanted to learn how much material it truly takes to make one of these so I also sourced all the biomass myself from two local farms, dropping literally hundreds of invasive buckthorn and honeysuckles as well as aggressive “weed” trees such as red mulberry and box elder over a week and then renting a 27hp Vermeer chipper to grind them up.  It was awesome!

This post is pretty epic itself – I opted for smaller photos in the post to keep the overall post length a bit shorter – click on them for a 600×800 shot.   This really should have been 2-3 posts, but I spent more time working than writing.  Skim or read it all the way through at your preference.  Total work covered in the build is 3 weeks, with another 1.5 in the biomass acquisition.  These are “puttering” time lengths – I am always working on 4-10 projects at a time :).

With the material on site it was time to get it soaking.  One of the keys to Jean Pain style brushwood composting is to soak the material for 2+ days to ensure that the chips are saturated to supply the pile with enough water to sustain it for months.  One of the problems I ran into early on is that of scale.  I can only soak about 6 yards of material at a time, which limited me to 1.5 batches a week with my days off and the shorter daylight of Fall.  All told it took over 3 weeks just to soak all the material.

Giant 375 gln (1420 l) totes I bought off of craigslist a few years back for $25 each. Why? Why not!

Once the material was soaking it was time to prep the ground.  I spent a day spreading the old Midden around the gardens.  This was unreal – never before have I had 8+ yards of compost to spread all at once.  EVERYTHING got mulched.  Yes, spreading compost by the wheel barrow load (40 of them!) is as fun as it sounds.  I will say it again and again – COMPOST is the true point of the Middens – gathering energy from them is merely function stacking an intrinsically useful activity.

As this pile was going to be 50% larger I had some concerns about it breathing well.  At one point I had myself talked into laying out 4″ perforated drain tile for air circulation, but thought better of it for several reasons.

Cupplant, Sunchoke, and Sunflower stalks forming the passive air circulating foundation to the Midden. After the winter it turns into humus and sequesters carbon. Regenerative waste stream? Check.

First – it added expense and resources.  I like to keep the plastic to a minimum; while not afraid to use energy or resources for the Greater Good, I also like to use natural products whenever its feasible.  Second, Jean Pain never did so I’m not even sure its necessary.  My solution was simple – I cut down a half dozen Cupplants that were nearby in the prairie garden that serves a insectary habitat near my permaculture guilds.  The thought is that these will allow air to come in slowly from the under the pile as they decompose themselves.  Basically the same reason you are often told to put twigs under a normal passive compost pile.

Now, the observant amongst you will notice a piece of .5″ conduit stuck in the ground with a tape measure  in front of it.   Of course there is a very good reason for this.  The Midden LC will have a 3′ (1 M) diameter core of brushwood that will be wrapped with 1″ tubing, but I am getting a bit ahead of myself.    With the base down, it was time to get building.

The Core

The core diameter of 3′ was chosen for the simple reason that hot composting seems to benefit from a minimum dimension of at least a meter.  Build a pile smaller than this, and you won’t get hot enough.   One of the downfalls of the Methane Midden is that the layout forced a width of only 2′ in most cases.  I thought that the straw bales insulation would be enough.  I was wrong.  Back to basics then.  Getting wood chips to form a cylinder can take some doing.  Luckily I had enough 2′ garden fencing in the garage to make a “mold”.  The thought was to cut the fencing to the circumference of a 3′ diameter circle.  Time for fun with math!

4' (1.2 m) tall Core. As I unwrapped the fencing, I would wind 150' (45 m) or so tubing around the chips to keep them in place.

A circle’s circumference is Pi x the Diameter of a circle; 3.14 x 3′ = about 9.5′.  Done.   Now, when you cut the fencing – leave the “nubbins” on the cuts – this works well to fold around once you get the circle made – think giant velcro.  The conduit I stuck in at ground zero and measured 18″ off each side to center the core column.  Then it was simply a matter of schlepping in the soaked chips.  About every 8″ (22 cm) or so I tamped the chips well with a 12# (5kg) sledge hammer.  Once I had 2′ tamped in place, I unhooked the fencing and unwound it.  Thanks to the tamping, the chips stay in place very well.  I then wrapped the fencing on the top of the cylinder with about 2″ (5 cm) of overlap on the bottom.  Then I started wrapping the heat exchanger around.

I love this shot. It really shows how stable the chips are with tamping (walking on it at this point). Jean Pain didn't use molds, just slapped it all in place with a pitchfork and walked on it.

This progressed 2 times until the core got about 5′ tall.  At this point I was becoming somewhat concerned that the column could topple, despite how stable it seemed.  Redoing it at this point would SUCK, so I opted to switch gears and work on the outer “donut” of biomass.  The thought here was to again use the 1 meter width of material to maximize the bio-reaction of the thermophilic bacteria.  Having 3′ of material on each side of the exchanger giving the Midden L’eau Chaude a total diameter of a bit over 9′ (2.75 m).  The other important reason to start building out the “donut” was that stacking, and especially tamping, the Core was getting difficult as it was over shoulder height for me at this point.  With a 2′ tall rim around the Core I could bring it up to its goal of 6’+ bringing the total heat exchanger length to over 550′ (168 m).  The heat exchanger needs a bit of explaining since it is critical to the Midden, so here goes.

The Heat Exchanger


550′ (168 m) of 1″ (2.5 cm) polyethylene irrigation tubing. Never one to be modest… this is a work of art.

This is the finished heat exchanger and I won’t even try to be modest.  It’s GORGEOUS!.  The water will come in the bottom, spiral up for 6′ and then take two larger loops back down to exit the pile.  Why this way?  It has a lot to do with temperature gradients.  Heat transfers best the larger the temperature differential (delta T).  The final goal is to that the water entering the pile at about 80 F (26 C) and exiting north of 120 F (49 C).  The bottom of these piles are cooler (heat rises!), but will still be rather warm.  As the water in the exchanger warms it is also climbing up through the pile, which is also getting hotter.  The thought is that there will always be a delta T of 20+ degrees between the pile and the water in the tubing.  Slick, huh?  Now wth is up with the big looping spirals?  The poly tubing kinks somewhat easily, so I chose to take 2 revolutions to expand the diameter of the spirals and slowly increase the degree of bend up to my final exit point. Now some final thoughts on the exchanger.  First, I would shift the hole thing up a foot.  Starting 4″ from ground level like I did will not add much heat to the water, whereas there is over a foot above the top of this column now that I am done.  I had thought that the top would be cooler, but that is not the case – no matter how much I pile on the heat just comes right through it: put your exchanger to within 6″ of the top without fear as long as the pile is hot.  Can you see I am already planning Midden #3?  But for now we need to bury that exchanger. Fleshing out the Midden

 

Taking shape! This is about 12 cu yards ( 8 cu m) with a current height of 5.5′ (1.7 m) and a 9′ (2.7 m) diameter. Awesome.

To keep the pile nice a tidy, and also to ensure that I could still walk around it, I again used a garden fence mold for the 9′ (2.7 m) diameter “donut”.  this time I opted for 3′ tall fencing.  The outer section takes an immense amount of material to fill – it was almost 2 weeks to get it to this point as the pile at this point was over 12 cu yards and weighed over 6 tons due to the sopping wet chips.  Remember that I could only do 5-6 yards at a time as the chips had to soak for several days.

 

I had intended to unwrap and re-wrap the fencing again, but in the end chose to leave it on and switch again to an insulating rim of straw, which I ended up stacking 3 tiers high.  It gets significantly colder here in southern Wisconsin than in Jean Pain Provence with winter lows dropping to -15 (-26) at least once or twice.  Time to break out the dump truck again!  Back to Craigslist and I contacted a farmer about 4 miles away with 70 bales of Oat Straw.  I would need about half that for the Midden, but filled up the truck to mulch the beds as well.

BART holds 48 bales of straw. I am not saying *everyone* needs a dump truck. But in my case I am making a good argument..

With the straw in place around the fencing, I then stacked a third tier of straw to form the mold for the final several yards of material.  In the shot at right the pile is nearing 7′ (2.1 m) tall which was the goal.  At this point I was nearing the end of the biomass and began to focus on rounding out the pile and maintaining the 3′ length from the heat exchanger as much as possible.   Was incredibly pleased with how the Midden was literally shaping up.  Sometimes a project just CLICKS.  This was one of those!

Gap left for the pump installation. You can FEEL the heat coming from the pile, the core of which is 150+ (66 C) at this point. Dang sucka.

Jean with one of his piles. As you can see his heat exchanger loops would have gone around the OUTSIDE of mine. Then again his piles crested 80 tons - 10x as big as mine. Jean was a visionary, and I am honored to be able to promote his work for a new generation.

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