Practitioners of the French biointensive method swear by double digging as a way of aerating and improving the soil and growing more and better quality vegetables than you ever imagined. But I had also read about local farmers pioneering no-till methods as a way to farm more sustainably, and read a soil food web book that advocated not disturbing the soil at all. So which is it--dig up the soil to a depth of 24 inches, or don't till?
Turns out the answer isn't quite so simple. The process of so-called double digging involves digging and removing only about 12 inches and then loosening (not digging and turning) another 12 inches. Plus, one is supposed to carefully move shovels full of soil from one trench to the next as one is digging, with the goal of disturbing the soil layers as little as possible. That's easier said than done, but there is definitely more to the method than sloppily moving soil around. Ideally, a garden bed will need to be double dug only once or twice and then can be left largely undisturbed, with additions of compost to the top of the bed providing the nutrients needed to maintain the bed in the long run.
A couple of weeks ago I wrote that one of the major lessons learned in my garden this year was that I need to take better care of my soil. After reading more about this particular technique and hearing from people who have used the double digging method with success, I decided to double dig some of my older garden beds once in order to loosen highly compacted soils. After double digging once, I'm going with a long-term plan of improving the soil through compost and green manures, but not more deep digging.
There are lots of books and websites that give more information and specific instructions on how to double dig (just Google the term), but here's what it looked like in one of my raised beds:
|About halfway finished|
|Trench emptied of top 10-12 inches of soil|
|Loosening bottom 10-12 inches of soil|
I moved across the bed digging and loosening one approximately 12-inch wide trench at a time, adding and incorporating soil amendments (homemade compost and purchased "humus") to the bottom of each trench as I went. If you're wondering if this took forever, yes, it took about 2 1/2 hours to do just one bed. Also, I was pretty tired afterwards! Given the amount of effort involved, I've decided to double dig only a few beds this fall and then monitor the results. If it turns out to be worthwhile (i.e. the double dug beds turn out to be super productive and healthy) then I will do more of them next year. Stay tuned for the results!