Sunday, 25 December 2011

Raised beds and no dig.

I'm not dead against raised beds or no dig schemes in the allotment.  I just think that permanent raised beds need high inputs of water, fertiliser and organic matter.  They are also time consuming needing a lot of attention to produce high yields from crowded plants.

Putting large amounts of decomposing organic matter on the surface may deplete the top soil of nitrogen.

Even if  you are  a strict recycler, all these things will be dependant on oil; if only due to transporting them.

Also, I can't be doing with all the paths.  I just look at them and think wasted growing space.

There is some thought that walking on the soil destroys its structure.  I cannot for the life of me go along with this.   In any case plants will grow through concrete - how compacted is that? Plants still grew even with dinosaurs compacting the ground.

Plants need water which they obtain from the soil through their roots.  Roots also obtain dissolved nutrients from the soil and they need energy to do this.  To obtain energy they need to respire using oxygen.  This means that plants need both water and oxygen in the soil.  The more fibrous the structure, the better the relationship between these soil constituents.  Walking on soil will squash out some of the air.  Walking across wet  soil will squash out some of the air and fill the pours with water muddying the soil.

However, needs must and sometimes you just have to work the soil in wet weather.  Going over the ground that you have walked on with a fork restores the structure and allows air to enter the ground.  However, common sense says trying to work muddied ground when it is pouring down with rain is pointless.

I would suggest that the structure of the soil is much more dependant on its organic and mineral content than whether it is walked on.  I read somewhere that if you get the calcium and magnesium content of the soil just right you can park you car on the soil and still have a friable soil.  I would like to try this out before I recommend it though - and that will never happen.

So I will continue to use larger areas, wider spacing, less watering and sharp tools to cultivate the soil and produce good harvests.

Having said all this my beds, which are about 15 foot by 25 foot, are all raised above the original ground level. One of the old blokes on the allotment site said why didn't I use old paving slabs on end to keep the soil from falling on the paths and track ways.  This was a good idea and I have, over the years, put paving slabs around most of the beds.

The ground was raised by the addition of lots of organic matter.  It didn't really matter to me what the organic matter was, it still got buried.  I have buried old cotton shirts, leather handbags and shoes;  leather belts; woollen jumpers and socks; tree and shrub shreddings; shredded paper; weeds except for bind weed and mares tail; tree trunks and branches; lots of tree leaves, muck and manures.  I used to bury woollen carpets too until I found they put nasty chemicals on them to prevent them being eaten by moths and fungi.

All these additions to the soil were buried at least two spits down and mostly further than this.  When I dig down now I find nothing except a darker stained subsoil. The nutrients and carbon locked up in the structure of organic material is slowly returned to the soil to increase its fertility.

Apart from vastly improving the drainage of the allotment and enabling me to use the ground year round, the raised bed is like a hot bed.  The decomposing organic matter generates a certain amount of heat and this can warm the soil enabling seeds to germinate earlier - or that is the theory anyway.

To make the raised hot bed, I don't pile organic matter on the top of the soil.  I bury it deep in the soil.  I do this because I do not want it to deplete the top soil nitrogen.  Putting organic matter on the surface of the soil may deplete the soil of nitrogen when it decomposes.  I know there are many benefits of mulching but it needs to be done with understanding and more care than is often suggested.  Piling on mulches is not a magic solution to all your gardening problems.  It is just one more strategy in the armoury of methods you can use on the allotment.

So my beds are raised but they are much bigger than any other raised beds that I have seen.

There is nothing wrong with raised small beds done well but I can't be doing with them.  They are too small for my way of gardening.

And this time of year I just like to go out and dig for an hour or so.  Allotments are not just for growing; they are for fresh air and exercise too.


  1. I agree raised beds can be a waste of time; they often seem to be used because they're fashionable, not because they're needed. I'm planning to build some, purely because of consistent problems overwintering a wide variety of plants, due to winter waterlogging. I get grass cuttings and dead leaves in large quantities from a local garden contractor who'd otherwise have to take them to the tip. It can work, but only in specific circumstances.

  2. Just so Robert raised beds should be constructed for a reason not just because they are a fashion accessory. Crafted with care they will do what you want them to. I just wonder if they will last as long as my beds have. Thirty years and counting.