More thoughts on double digging raised bed gardens.

permascience
June 08, 2008
http://www.youtube.com/watch?v=ugFd1JdFaE0

"Emilia Hazelip (1938 - February 1, 2003) was an organic Permaculture gardener who was born in Spain and began gardening seriously in the late '60s. A former Merry Prankster and pioneer of the concept of synergistic gardening, her farming methods were inspired by the work of Masanobu Fukuoka.

Where Fukuoka focused most of his attention on orchards and the rice/barley crop rotation, Emilia Hazelip focused on creating and maintaining market gardens of vegetables and herbs.

Emilia Hazelip, who introduced the concept of permaculture to France over a decade ago, drew on many sources as she continued to develop gardens. The work of Permaculturist Marc Bonfils with self-fertile cereal production and the microbiological research of Alan Smith and Elaine Ingham are frequently mentioned.

To see more videos by the maker of this film and for contact information on how to purchase a high quality full length version (SVHS) on DVD please visit: http://www.youtube.com/user/BULLEBOULO

For More Information on the Global Permaculture Movement Please Visit:
http://www.permacultureplanet.com";

==

That is the way to build a raised bed though there are important details (the ones the devil is in) that need to be considered, many based on soil type and climate and lay of the land.
She is exactly right about the dimensions of the bed in the design she recommends except that one needs the ditch (a very narrow path) between the beds _to extend below grade 25% to 40% of the total bed height_ thus extending the actual working height of the beds considerably. You provide extra aeration for the part of the bed below grade that is exposed to the ditch between the beds. The other dimensions she suggests are perfect, 4 feet wide (measured approximately
across the bed exactly at existing grade level. This bed width can be modified according to the height of the gardener(s) so that they will be able to do any work needed, leaning over to reach the middle, but not having to put their foot on the bed to keep from falling forward, which would induce compaction in those places (and that is a real issue with your prized, hard-won, mature, permanent beds). The 20 inches between beds (measured at existing grade as shown in the diagram) is ideal. Of course you put all weeds removed from the garden into this ditch to conserve water, create a walking path protecting the soil underneath from compaction and as they decompose they provide beneficial microorganisms and nutrients (compost tea) to leach into the garden soil for added tilth and fertility, food for soil dwelling creatures and particulate matter for them to use in constructing their habitat; soil colloid and soil crumb structure are keywords in this instance.

Yeah, somebody posted that youtube vid here some time ago.  Excellent video!

Now .... why double dig?  I don't remember that in the video?

As for the advantages of a raised bed and people not walking on it, Sepp seems to have now taken that to a new extreme:  six foot tall, steep sided raised beds with a peak in the middle.  It would be a challenge to step on it!  And with hugelkultur in the middle, it is shrinking a little each year - the shrinking leading to small soil shifts in the bed - the perks of tilling without actually tilling!

I'm partial to not turning the soil if it can be avoided though I am not entirely against a one time digging if working in clayey soil, as long as the soil horizons are put back in order.

I've worked with a similar style as the video shows, except without the initial tilling.

The beds in my backyard range from 3' wide to 6' wide.  I'm tall and have found that 4.5-5 is about right for me.  If other people are picking, 4' is an excellent bed width.

My paths are 29" wide.  This allows my wheelbarrel and electric lawn mower to fit.  If other people are working in the beds, more space will be needed, 4' wide is not unrealistic to allow a person to pass another, plus allow space for baskets/buckets.

My backyard beds are double dug.  I have sandy soil and it was still enough to work up a good sweat.  In NY, it was a heavy clay and I was looking at 1.5 acres of beds.  There is no way I was going to double dig that all by myself with just a tiller and wheelbarrel for equipment.

For large areas, I find that earthworms are a fantastic tool.  I had the field plowed and tilled as deeply as possible mechanically.  The beds were raised further by shoveling from the paths onto the beds, then further raised by adding compost.  The field had a slope, on the downhill side of the beds the difference in height was about 9 inches.  Add another 6 inches of loosened soil below grade, I had a good 15 inches of worked soil.  While I would prefer 2 feet of depth, there is a limit to what a man can do.  The worms can do the rest.

The NY soil had a worm count of about 20 per square foot.  It was beautiful soil let me tell you.  Keep it mulched, keep adding compost, keep the chemicals out of there, the worms will do the job of burrowing, churning, aerating and pooping.  Across an acre of that field there are about 870k worms.  At 2500 worms per pound, about 350 pounds of worms.  They consume their body weight each day in soil and organic matter during the warm season, pooping out 70% of that in castings.  This amounts to 200 pounds or more each day, 6000 pounds per month of 1-1-1 natural organic fertilizer, full of microbial life chealting the nutrients, ready to be assimilated by the plants.  During the cool season, they go deep, burrowing as they go.  If I had to double dig the field by hand it would probably be the end of me.  A 4x50 bed could be dug by a man in a day, but getting it planted, tended, mulched and harvested would be beyond the abilities of anyone I know.  Even if I had a helper whose job was to double dig the beds, it would take a season to prep that 1.5 acre field.  The worms will do it.  They don't sleep, they don't need housing or a paycheck, and they will bring all their friends to help out if you do the work of feeding the soil.

I'd be interested to see a side by side comparison of teh same crop grown in a double dug bed and a sheet mulch bed of the same fertility levels.

Maybe I'm lazy and short-sighted but unless you're dealing with hardpan I don't see any reason to double dig. Radishes are great at loosening soil, there are stubby varieties of carrot, potatoes can be grown on top of soil if covered in enough mulch, and lettuces grow fairly well in compacted soil.

I've worked with both methods and will never put my back through a double digging again.