Starting off a new Hugelkultur in the potato bed.

Bloke came down with a lorry load of shredded woody material and had some logs on the back as well.  He gave me the logs so I decided to make another trench Hugelkultur in the potato bed.  I wanted to raise the soil at the north end of the bed in order to create a surface water calming bank alongside the espaliered fruit trees.  The Hugelkultur trench will be a subsurface water calming structure until it decomposes. 
I dug down one spit today and left the soil on the side of the trench.

I always use garden lines because I can't keep a straight line without them.  There are lots of reasons for not digging but there is no other way of introducing large quantities of organic matter and deepening the top soil.  I will take another spit out of the bottom of the trench and then fork over the bottom which will give me three spits of turned over soil.  Loads of waste material from around the allotment will be used to put into the trench. 

The old vegetables from last season.  A few celery and celeriac together with carrots and beetroot. 

Old bits of wood that I have collected from under the hedge and in the woody chippings piles.  I will probably get some more before I fill in the trench.  I will certainly clean the bottom of the hedge a little more. 

The logs off the lorry.  These will go at the bottom of the trench.  I think they are mostly cherry laurel. 

I will move the frames off the hot bed, which has not been that hot during the winter.  The woody chippings have rotted down now and will go at the bottom of the trench.  I will put the frames on top soil now and just rely on the glass to heat the soil.

If that is not enough shreddings, I will resort to the woody chippings pile to add more woody material.

Mostly X Cupressocyparis laylandii and holly but it is all grist to the mill.  I will also be putting the cuttings from my daughter's garden in the trench too.  It will all be two spits down and can moulder there for a year under the potatoes and whichever green manure I plant after them. 

The top soil is deepening and now is more than a spit deep.  The subsoil is darkening with organic matter too.  Deeper topsoil means more organic matter, more nutrients, more microbes, more water and more air for vegetable roots to delve into. 

Now I am going to try and explain why I think that it is a good idea to introduce organic matter into the subsoil as deep as I can.  In normal conditions plants can get water and dissolved nutrients easily from the top soil.  There is usually decomposition going on and nutrients being released.  As drought conditions start to appear the roots start to forage for water lower and lower in the soil profile.  The dry top soil means that they cannot obtain nutrients from here because there is no water to dissolve them in.  Nutrients can only enter the root as dissolved ions.   As the roots pass out of the dry topsoil they pass into the moist but infertile subsoil where nutrients are much more scarce.  Little is dissolved in this water and although the plants have adequate water they begin to get nutrient shortages.  Bottom old leaves start to yellow as nitrogen is transported away to the growing tips, although the plant is not wilting.  If we can deepen the soil, adding lots of organic matter, it will make plants more able to withstand drought conditions and the shortage of nutrients that it might bring.

So that's what I have been doing today - that and turning one of the compost bins.  I will use the compost to mix in with the top soil as I rake it back into the trench. 

The possibilities of using slope to benefit the allotment.

My allotment slopes to the south east.  What advantages does that give to the allotment crops?  The aspect of the allotment can give quite an advantage.  Being south facing means that the sun's heat and light is a little more concentrated and will warm up the soil earlier in the year and allow crops to be grown later in the autumn. 

Path alongside the allotments looking down the south facing slope.

Although I grow crops in north south rows,  I have put in paths from east to west at right angles to the slope.  The paths have been made as mini ditches and soil has been taken out and put onto the growing areas to raise them.  The mini ditches are aligned more or less with the contours across the allotment.  Water will flow at right angles to the contours soaking in as it does.  Some surface water will flow into the ditches and spread out.   I have filled the  ditches  with woody shreddings which will soak up some of the water and prevent it from evaporating creating a reservoir of stored water. 

Espaliers planted on the top of the raised bank.

This allows surface rain water to be spread out evenly along the path, slowed down and soaked into the soil.  Although irrigation is not a particular priority in the UK climate, we still have to consider the effects of leaching and soil erosion. 

Raising the level of the soil, creating banks on the downside of the slope and planting espaliered fruit trees or soft fruit along the east west raised soil aids in the slowing down of water (mass flow) through the soil.  As the water is slowed, it allows dissolved nutrients to be taken up by plants before it is lost though leaching. 

As plant nutrients are soluble minerals they will be leached slowly as the water flows to the bottom of the slope.  I have planted comfrey at the bottom of the slope to catch as much leached nutrient as I can.  Their deep roots will absorb much of the available nitrogen and any potassium and phosphorus that is available.  The leaves and stems of the comfrey can then be composted, made into comfrey liquid or put into the worm bin to recycle the nutrients. 
It is all about slowing the mass flow of water through the soil.  This will slow leaching, allow more time for uptake of soluble minerals; capture eroded soil particles, enhance water filtration  and provide more opportunity for upward water capillary action for plant growth.


My compost heaps are at the top of the slope so that any leachate that they produce will flow down the slope and into the allotment soil.  In a similar way, I have planted perennial nitrogen fixing legumes along the top of the slope so that any nitrogen they fix will flow naturally into the allotment top soil.  I will be planting perennial legumes alongside the fruit trees and bushes on the banks alongside the paths so that nitrogen will flow with the water into the growing areas. 

Compost bins at the top of the slope so that leachate will flow into the allotment.

Laburnum and lupins planted at the top of the slope so that nitrogen they fix will

flow into the allotment growing areas.

In the UK there is often too much water flowing through the allotment.  It is necessary to put in some kind of drainage to prevent waterlogging.  I have dug out a trench at the bottom of the allotment and filled it with stone sieved from the top soil.  The stone was covered with paving slabs to make a path alongside the hedge. 

Drainage ditch under the slabs.  Path is at the bottom of the slope.   

During the driest months in summer, the soil is covered by mulches to reduce evaporation and the trench Hugelkultur further slows the soil water and retains it as a reservoir that is accessible to plant crop roots. 

So slopes can be very useful.