Trench Hugelkultur and hot bed.

I think that a lot of misconceptions are being perpetuated by people that see composting more as a crusade rather than just a method of recycling.  There are some reasons why good well made compost was valued in the past. It was used in various mixes to make seed and potting compost.  Fine grained well rotted material was needed to produce this.  Woody material was avoided because it did not rot down very quickly and tended to reduce the level of nutrient in the compost.  The main decomposers of woody material are the fungi and they send out foraging hyphae that glean nitrogen and other nutrients to make the fungi’s structure. The extent of nitrogen depletion in soils with buried woody material seems to be questionable and the results of experiments are not very clear.  It would seem that sometimes there is relatively little nitrogen loss. 

We must also not loose sight of the fact that invertibrates also have an important role in the decomposition of woody material and these organisms would add to nitrogen to the soil when they excrete and finally die.   

A few years ago I downsized the amount of land I cultivated and this meant that I resented any space that was not being utilized for crop growing.  I made the decision to bury all my waste plant material rather than compost it so that I could dismantle the compost bins and use the area for planting. 

While woody material can be burnt there are several very good reasons for not burning.
Garden fires produce carcinogens - cancer producing substances. You lose the nutrients locked up inside the plants when they burn. 90% of nutrients are lost to the air through gases and smoke. It adds carbon dioxide to the atmosphere unnecessarily . You do not get rid of stuff. It is still there - just changed- and some of your pollution gets dumped onto surrounding allotments.

So I have, for many years, been burying woody plant material in order to recycle it and not have to burn it.  I call it the Montezuma method because the South American native civilizations used it to make their gardens on lakes, on mountains and in most inhospitable and infertile areas.  Chinampas were developed using woody material to produce growing platforms that sludge could be put onto to raise the level of the Chinampas above the water of  lakes.   These gardens were very productive and some are still in existence today.   Ancient civilizations throughout South America used similar brush wood techniques to produce terracing on steep sided mountains.  Not only did the brush wood rot down to produce very friable soil but it also helped in drainage and moisture retention. 

A composting method that is similar to the South American method is the Hugelkulture.  It is an old form of composting that was developed in Eastern Europe.  Brushwood either fresh or beginning to rot was gathered into a pile or put into a pit, covered with other compost material like tree leaves, and  finally a layer of soil was used to cover the pile.  The permaculturalists suggest that the soil could be planted immediately with a variety of quick growing vegetables.

You can see the results of the Hugelkultur that I did two years ago.  .  The brushwood has broken down into small pieces and mixed in with the soil.  

The larger logs have not rotted down yet.  

The trench is about two and a half feet deep.  Making it this deep means that a lot of material can be buried.  

I bury my logs and brushwood deep for several reasons.  If fungi are rotting down the wood, I would like them to glean any of the nitrogen that has leached from the top soil because then I might have some opportunity to recycle it into the top soil when I dig deeply again. The brushwood’s ability to absorb moisture from the soil and then allow it to return to the soil in a more controlled way means that deep rooted plants like runner beans will have a source of water throughout the growing season.    Burying deeply also means that cultivation of the top soil is relatively easy because digging over an area that is full of brushwood would be difficult. 

This new trench was taken out because I had cut down some oak branches from an overhanging oak tree Quercus robur.  You can see from the pictures that the Hugelkultur I did two years ago is still under the soil slowly rotting away.  This is where I grew the exhibition sweet peas last year.

 I don't know whether it is important or not to put the larger logs at the bottom of the trench but this is what I did and it worked fairly well two years ago.

I like to add weed turfs to the mix as well.  I hasten to add these weed turfs are from another allotment.  The weed turfs add a lot of top soil to the trench and fill in the voids between the logs.

The next layer to go on is the brushwood.  You can see it on the left of the photograph.   I used a lopper to cut the bigger branches so they would fit into the trench.

I got the whole pile of oak branches into the trench with a lot of room to spare.  I also wanted this to be a hot bed to bring on some early cauliflowers.  To do this you need material which is going to generate heat.

The lawn mowings were steaming because they were so hot.  These covered the brushwood and were trodden down.  

A good layer of cow muck covered the grass cuttings.

And finally a thick layer turf and a dusting of ashes from a bonfire on another allotment.  I want to keep the ground alkaline because of the brassicas and the ashes will help to do this.

There is no need to burn woody material; as you can see here, it can be very effectively buried to form a raised bed. The nutrients from the wood will slowly be released into the soil over many years giving sustained fertility to the soil.

As you can see I began replacing the soil before taking the photograph.  By the time I had finished covering with top soil it had got too dark for photographs.  I will have to add the final photograph later.

It is amazing that attempts to drain the allotment and make it water free during the winter resulted in research and practice in making Hugelkultur beds like this one.  It should grow some good cauliflowers.

December 2012 - this Hugelkultur bed did well in the summer of 2012 and produced about 30 large cauliflowers.  Unfortunately the only photograph I have is the cauliflowers covered with enviromesh to keep the cabbage white caterpillars  Peiris brassicae off the plants.

You can't really see that much in this photograph but it does indicate that burying logs and brushwood still allows a lot of growth and does not deplete the soil of nitrogen to the extent that textbooks would have you believe. It is true that adding carbon to soil will tend to deplete available nitrogen for a while; adding nitrogen will deplete carbon and adding air will tend to deplete both.   Cauliflowers are very nitrogen hungry and would not have produced this much growth if there was any lack of nitrogen.


Another Hugelkulture bed for the climbing French beans


I wanted to bury the old blackcurrant bushes and the cuttings with big bud on them.  There were some other things that needed burying so I decided to do some trenching.

One spit down.

I am going to put the climbing French beans here so a good deep root run will be good for them.  The top soil is on the right of the picture.
Now we go down another spit.

The old huglekulture wood can be seen.

When I dug out the second spit, I found last years hugelkultur wood.  It had rotted away to a fibrous peaty mass. I am going to mix this with the subsoil when I put the soil back in the trench.

Having a layer of woody material under the Brussel sprouts does not seem to have affected them detrimentally.  In fact I think that it might have encouraged them to grow larger.

I used the fork to turn over the bottom of the trench.  You can see the sandy clay that is the subsoil on the allotment.  I don't usually turn this up because the top soil is so deep on the allotment.  This area used to be where my old greenhouse was and I never double dug here while the green house was up.  This means that the top soil is not very deep.

I put the old blackcurrant bushes at the bottom and then got some more brush wood.  These are twigs and branches from a laburnum tree overhanging the fence.  Laburnum is a legume nitrogen fixing plant. Does this mean that I am adding extra nitrogen to the soil?

I then added a good layer of weeds that included couch grass and docks.  They may grow but I don't think so. On top of them I put a thick layer of leaves.  I'm not too sure about these leaves.  They have been rotting away in the bins by the gate for a while but they still look a little ropey.

Still needs must... Finally I put a layer of upturned turfs on the top.

If the weeds can grow through that lot then they deserve to be given a chance.  They wont be though.  Now I put the subsoil back but I am going to sieve it and add horse and pigeon muck.

The subsoil looks much better when it is sieved and mixed with manure. I am sieving through an old bread tray.  The holes in the bottom of the tray are about 1 inch square.  I just push the soil backwards and forwards in the tray until it falls through the holes.   I will sieve the top soil on top of the  subsoil mixing in more horse and pigeon muck.

And that is how I do hugelkultur.  I am hoping that this will heat up a bit and allow me to get an early crop of lettuce off it.

Trail of Tears climbing beans

The Trail of Tears climbing beans at the end of June are growing really well.  They do not like the very wet cold weather that we are having at the moment (July 2012) but the plants are really healthy.  So, it would seem that all the woody material that I added to the trench has either had no detrimental affect or little affect on the growth of the beans.  We have been having a particularly wet summer this year and the brushwood added to the trench might be helping with drainage.  I wish that I had made a similar trench for my Scarlet Emperor runner beans.

Trail of Tears September 2012

Both ends of the row were badly affected with slugs due to an exceptionally wet year.  Regardless, I had an exceptional crop of beans.  Little evidence of nitrogen depletion here.

So, how long do Hugelkultur beds last for?  The rate at which fungi can degrade lignin in wood is very slow and this means that the bed can last for tens of years.  However, if wood is already beginning to degrade, the soil is very open and fertile and compost or manure is also added then the rate of decay will alter.  My Hugelkultur beds lasted at least three years before the wood had begun to crumble into a very friable material that was really easy to mix into the top soil.  This does not surprise me because the UK climate is wet and cool and this encourages decomposition by fungi. Other climates may have a different effect on the rate of decay.