I double dug raised beds 27 years ago then heavily mulched with anything organic for 10 years. I had fantanstic yields. My in-laws who all are farmers came to study my methods. I had the first and biggest tomatoes.
Gardening became less of a priortiy due to family and job responsibilities. I just did it half a**d. Now I want to garden again.
I've tried tilling the raised beds with a Honda mini tiller for the past 3 years. it's a fine littel machine but I'm going to lasagna beds and containers now that I'm 61 years old. I expect to have those fantastic yields again in 2009.

Probably more than you wanted to know.
Be sure to pray over your garden and thank your soil and plants for their gifts to you.

The primary concept that drives the double digging theory is to get organic matter and air deep into the soil where it does not normally go. The vast majority of the aerobic bacteria, and your organic matter, will be in the top 6 to 8 inches of your soil, where most all of a plants roots will also be. While the earthworms and many other members of the Soil Food Web will be working deeper that is not the primary place of employment for them, so double digging, except in very rare circumstances, is a waste of time and energy.

Double digging is not meant to get organic material deep into the soil; in fact, the topsoil is supposed to be set aside to be replaced once the subsoil is opened up. Double dug soils are not inverted. Double digging is a lot of work if done by hand but need not be repeated, perhaps for many years.

I am running an experiment will side-by-side beds, one pair double dug and another pair not. We still see difference in plant response some 4 years later.

I thought double digging was meant to help deep rooted plants get into compacted subsoil.

It is. I remove about 8-10 inches (20-25 cm) of top soil, reserve to the side, I remove another strip about the same thickness. Then with a sturdy fork or digging bar, I break up/loosen the deeper subsoil. Then I reverse the process. I should end up with a strip of elevated soil loosened to a depth of 24-30 inches below the original surface.

I like to add minerals to the middle layer where they are handy to penetrating roots with associated microbial activity. Organic material and soluble soil amendments go into the surface layer.

Depends on your soil. I moved into new construction with no top soil and hard clay. I had to double dig any flower bed that I wanted to grow anything in. It was done more to break up the compact soil and improve drainage. I wish I had dug up all the shrubs I got with the house and double dug the whole yard.

It's a lot of work, but it's worth it. A spade fork works well and soaking the soil a week before you do it (with a soaker hose) helps too.

Surprisingly, one part of our yard has great soil, so all we had to do was rent a tiller and bust that up before we planted.

I do an initial double digging in order to remove the many large rocks and to quickly enrich
my sand,gravelly soil.

I built raised beds and they are full of loose, rich soil. Here in my area a few inches below the surface there is dense clay. I used to double dig and it was hard dirty work, and the next year I would have to till in even more organic matter. It was endless hard drudgery. The raised beds make gardening a pleasure especially now that I am older. I too am trying to grow a significant amount of food this year, but I will never again fight clay gumbo.

>The primary concept that drives the double digging theory is to get organic matter and air deep into the soil where it does not normally go.

This is very far from the concept.

I am a strong proponent of double digging and as has been said, the proper method, as advanced by the Bio-Intensive method in Jeavon's book and as I learned many years ago at the Bio-Dynamic farms in Spring Valley, NY, is to maintain the soil's natural layers while loosening the soil to considerable depths. It most definitely is not about incorporating organic matter deep into the beds where it does not belong. One works compost or other organic matter into the top few inches only where it will be of most benefit.

This method of soil preparation is key to the extremely dense plantings of beds using these methods. Sun, nutrients, moisture and room for the roots to stretch their legs. All must be addressed.

When I began my market gardens back in the 1970's, I was a big fan of Ruth Stout's methods of heavy mulching (and still am.) But faced with tired and heavily compacted clay soil from decades of hay mowing, I quickly learned that double-digging at least some of those beds as a first step would be the answer to quickly getting that soil into production. The rest we lightly tilled with a rototiller and began a semi-permanent mulch. (Semi-permanent in that we had to pull it back for a spell in early spring to allow the frozen ground to thaw and warm in the cold northern climate.)

By way of an unplanned "controlled experiment," we discovered that in the the same compacted soil that we had double-dug and were growing respectable carrots, just a short distance away, under a permanent mulch, five or six years later the untilled soil was still seriously compacted about six inches down. Hence my skepticism at the lasagna lady's "plant in mulch" methods or others who say "mulch and let the worms till it for you." I guess either they were wrong or our worms were slackers. Either way, I think the concept of "no work gardening" is the equivilent of a "no produce" farm.

We found that double digging a raised bed once was sufficient for our soil for at least several years with the addition of a fair amount of compost with a garden rake every year into the top few inches, mulching to keep the soil moist and weeds down and also by the annual Running Of The Hens through the garden in the late Fall and early Spring. We would usually double-dig again when carrots came around again in the rotation or simply when the urge to get into the soil again was just too overwhelming in the early spring.

Unlike others, we enjoyed the labor. As Jeavons wrote, "Properly performed, labor is not tedious or enervating, but strengthening and rewarding."

My suggestion is to submit your soil to the carrot test. Plant a small patch of carrots in a double-dug bed, another in a bed only prepared by mulching, and if you're so inclined, another carrot patch in layers of pure compost, leaves, straw or whatever pasta the lasagna lady would have you believe is a substitute for your soil. Let the harvest be your guide.

Mulching without tilling may be "nature's way of gardening," but Ma Nature grows precious few carrots out there in her all-natural fields. Milkweed maybe, then briars and then saplings, but carrots, beets, and eggplants? I don't think she would mind a little assistance.

Wayne

A goooood one, Wayne.

Thank you marshallz. I sometimes run on with the prose, but this is a subject close to the heart.

Nittyg, I'm interestedd in the tool you are working on. I've only used a spade and a fork in prepping the beds. There is a U-Bar available that was developed by Elliot Coleman here in my new home-state of Maine. Johnny's Selected Seeds sells one. I've been thinking of heading east to see one in action next time I off in that direction. Not really sure if it would be a suitable tool for me right now, since this spring will be the first chance I get to even see my soil. I suspect (from USDA area soil maps) that I have a gravely, sandy loam, but we'll see. I just moved into this place the first of December, the ground immediatly froze and then was covered with a deep blanket of snow before I could do any exploratory digging. Best I can hope for now is to head out on snowshoes this week and stake out the beds through the 3 feet of snow and wait until spring to start the new garden. Hope the spring brings a glimpse of friable soil. (Hope springs eternal, spring brings eternal hope... Hey, did I coin a phrase?)

Anyway, there hasn't been a garden in my life in the last 30 years that didn't involve double-digging AND mulching

Wayne

Well said, Wayne. Your professional experience echoes my minor back yard experiments.

I have a long continuous bed on the north side of the yard, which I artificially divide into "beds" between fenceposts. Each year I try different strategies to improve each bed, and watch closely to see the results.

All the beds are mulched year-round, in fall and early spring with tree leaves. All get topdressed with compost and UCG and alfalfa, then wood chips.

The best immediate results have come with overwintered lasagna compost heaps. Even on beds which were not dug at all (and had been heavily compacted by foot traffic) a couple of feet of lasagna layers produced healthy quick growth in the spring and good harvests.

However, I have noticed that deep (2-3 8" shovel depths) tillage, generally following Jeavons's methods, made a difference in both the immediate season, and in following years. Wherever I've dug deep, the plants seem to do better, for longer.

To be fair, this is working in a heavy clay soil which has been gardened for somewhere around a century, and the soil has clearly been improved with longterm additions of organic materials. To the depth of a shovel it tills easily; but beneath one shovel depth it is very resistant.

Wayne mentioned being "...faced with tired and heavily compacted clay soil from decades of hay mowing..." and I think this touches on one of the key benefits of double digging: it can quickly break up clay hardpan at the depth of a plow (or in urban gardening situations, a shovel) and allow plant roots, earthworms, and the rest of the microherd to penetrate.

However, like everthing else in life & gardening, there are tradeoffs. If you cultivate, you damage the slow-growing mycorrhizal fungi which contribute to most garden plants. Cultivation also hastens the breakdown of organic materials, including longterm humus. So, I would not want to double dig every garden bed here, every year. Nor would I want to double dig at all, in sandy soil.

One final note: whether you till or not, keep off the garden! Stepping onto clay, especially very damp or wet clay, destroys many of the benefits of both tillage and longterm mulching. Even when I choose to dig, I use a wide stiff piece of plywood to distribute my weight.

All the best,
-Patrick